CORNELL
UNIVERSITY

LIBRARY

ZOOLOGY

 
nia
WATER REPTILES OF THE PAST
AND PRESENT
THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS

 

Agents

THE CAMBRIDGE UNIVERSITY PRESS
LONDON AND EDINBURGH

THE MARUZEN-KABUSHIKI-KAISHA
TOKYO, OSAKA, KYOTO

KARL W. HIERSEMANN
LEIPZIG

THE BAKER & TAYLOR COMPANY
NEW YORK
WATER REPTILES

OF

THE PAST AND PRESENT

BY

SAMUEL WENDELL WILLISTON

Professor of Paleontology in the University of Chicago

 

THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS
CopyricHT 1914 BY
THE UNIVERSITY OF CHICAGO

All Rights Reserved

Published October 1914

‘Composed and Printed By
The University of Chicago Press
Chicago, Illinois, U.S.A.
PREFACE

It was just forty years ago that the writer of these lines, then
an assistant of his beloved teacher, the late Professor B. F. Mudge,
dug from the chalk rocks of the Great Plains his first specimens of
water reptiles, mosasaurs and plesiosaurs. To the youthful col-
lector, whose first glimpse of ancient vertebrate life had been the
result of accident, these specimens opened up a new world and
diverted the course of his life. They were rudely collected, after
the way of those times, for modern methods were impracticable
with the rifle in one hand and the pick in the other. Nor was
much known in those days of these or other ancient creatures, for
the science of vertebrate paleontology was yet very young. There
were few students of fossil vertebrates—Leidy, Cope, and Marsh
were the only ones in the United States—and but few collectors,
of whom the writer alone survives.

Those broken and incomplete specimens, now preserved in the
museum of Yale University, will best explain why this little book
was written. The author offers it, so far as lies within him, as an
authoritative and accurate account of some of the creatures of
eatlier ages which sought new opportunities by going down from
the land into the water. So far as possible he has endeavored to
make the text understandable, and, he hopes, of interest also, to the
non-scientific reader. He will not apologize for such scientific
terms as remain, since only by their use can precision be attained:
there are no common English equivalents for them. The reader
will find their explanations in the chapter on the skeleton of reptiles,
and especially in the illustrations.

The author has had the opportunity during recent years of
critically studying nearly all the reptiles described in the following
pages, but, if that were the only source of his information, the
accounts of many would have been meager. He has endeavored,
briefly at least, to mention the names of all those to whom we are
chiefly indebted for our knowledge, but in such a work as this it is
manifestly impracticable to give due credit to every one.

Vv
vi WATER REPTILES OF THE PAST AND PRESENT

To the friends who have been of assistance in various ways he
tenders his sincere thanks: to Professor E. Fraas for photographs
and the kind permission to reproduce some of his excellent illus-
trations; to Dr. Dreverman, of the Senckenberg Museum, for
several excellent photographs for reproduction or restoration; to
Dr. Hauff, of Holzmaden, for an excellent photograph of an
ichthyosaur; to Dr. H. F. Osborn, of the American Museum, for
permission to reproduce. the spirited restoration of ichthyosaurs
drawn by Mr. Knight; to Professors Schuchert and Lull, and
Dr. Wieland, of Yale University; to Dr. Hay and Mr. Gilmore, of
the National Museum, to Mr. Barnum Brown and Dr. McGregor,
of the American Museum, and to Professor Merriam, of the
University of California, for photographs and other favors.

SAMUEL W. WILLISTON
UNIVERSITY oF CHICAGO

July, 1914
CONTENTS

CHAPTER
I. IntRopucTION .

II. CLASSIFICATION OF REPTILES
III. Tae SKELETON oF REPTILES

IV. THe AGE oF REPTILES

V. ADAPTATION OF LAND REPTILES TO LIFE IN THE WATER

VI. ORDER SAUROPTERYGIA .
Plesiosauria.
Nothosauria.

VII. OrpER ANOMODONTIA
Lystrosaurus.

VIII. ORDER IcHTHYOSAURIA .

IX. OrDER PROGANOSAURIA .
Mesosaurus.

X. ORDER PROTOROSAURIA .
Protorosaurus.
Pleurosaurus.

XI. ORDER SQUAMATA
Lizards.
Mosasaurs.
Snakes.

XII. ORDER THALATTOSAURIA

XIII. OrpER RHYNCHOCEPHALIA
Choristodera.

XIV. ORDER PARASUCHIA
Phytosauria.

XV. ORDER CROCODILIA
Eusuchia.
Mesosuchia.
Thalattosuchia.

XVI. ORDER CHELONIA . ‘
Side-necked Turtles.
Snapping Turtles.
Fresh-water or Marsh Tortoises.
Land Tortoises.
Sea-Turtles.
Ancient Sea-Turtles.
Leather-back Marine Turtles.

River Turtles.
vii

PAGE

13
19
44
59
73

102

107

. 126

. 132

138

. 176

184

194

216
CHAPTER I
INTRODUCTION

In most persons the word reptile incites only feelings of disgust
and abhorrence; to many it means a serpent, a cold, gliding,
treacherous, and venomous creature shunning sunlight and always
ready to poison. Our repugnance to serpents is so much a part
of our instincts, or at least of our early education, that we are
prone to impute to all crawling creatures those evil propensities
which in reality only a very few possess. Were there no venomous
serpents—and there are but two other venomous reptiles known—
we should doubtless see much to admire in those animals now so
commonly despised; because a few dozen kinds, like the rattle-
snakes, copperheads, and cobras, protect themselves in ways not
unlike those used by man to protect himself, we unjustly abhor
the thousands of other kinds, most of which are not only innocent
of all offense toward man, but are often useful to him.

There are now living upon the earth more than four thousand
kinds or species of cold-blooded animals which we call reptiles, all
of which are easily distinguishable into four principal groups: the
serpents and lizards, the crocodiles, the turtles, and the tuatera.
Their habits and forms are very diverse, but they all possess in
common certain structural characters which sharply distinguish
them from all other living creatures. A reptile may be tersely
defined as a cold-blooded, backboned animal which breathes air
throughout life. And yet, it is not quite certain that this defini-
tion is strictly correct when applied to all the reptiles of the past,
since it has been believed that certain extinct ones may have been
warm-blooded. By this definition, short as it is, we at once
exclude a large number of cold-blooded, air-breathing, backboned
animals which were formerly included by scientific men among the
true reptiles, and even yet are popularly often so included—the
amphibians or batrachians. These animals, now almost wholly
represented by the despised toads, frogs, and salamanders, were,

I
2 WATER REPTILES OF THE PAST AND PRESENT

very long ago, among the rulers of the land, of great size and
extraordinary forms. But they have dwindled away, both in size
and in numbers, till only a comparatively few of their descendants
are left, none of them more than two or three feet in length, and
all of them sluggish in disposition and of inoffensive habits. While
we may speak of the amphibians as air-breathing, they are, with
few exceptions, water-breathers during the earlier part of their
existence. Some may pass their whole lives as water-breathers,
while a few begin to breathe air as soon as hatched from the egg;
but these are the marked exceptions.

In many respects the internal structure of the amphibians of
the present time is widely different from that of reptiles, though
there can be no doubt that the early amphibian ancestors of the
modern toads, frogs, and salamanders were also the ancestors of all
living and extinct reptiles, and it is a fact that the living amphib-
ians differ more from some of the ancient ones than those early
amphibians did from their contemporary reptiles. Discoveries
in recent years have bridged over nearly all the essential differ-
ences between the two classes so completely that many forms can-
not be classified unless one has their nearly complete skeletons.
We know that some of the oldest amphibians, belonging to the
great division called Stegocephalia, were really water-breathers
during a part of their lives, because distinct impressions of their
branchiae, or water-breathing organs, have been discovered in
the rocks with their skeletal remains, but we are not at all sure that
some of the more highly developed kinds were not air-breathers
from the time they left the egg; indeed, we rather suspect that
such was the case.

We are also now quite certain that, from some of the early
extinct reptiles—the immediate forbears probably of the great
dinosaurs—the class of birds arose, since the structural relation-
ships between birds and reptiles are almost as close as those between
reptiles and amphibians.

Huxley believed that the great class of mammals arose directly
from the amphibians, and there are some zodlogists even yet who
think that he was right. But paleontologists are now quite sure
that they were evolved from a group of primitive reptiles, known
INTRODUCTION 3

chiefly from Africa, called the Theriodontia; quite sure because
nearly all the connecting links between the two classes have already
been discovered—to such an extent, indeed, that really nothing
distinctive of either class is left save the presence or absence of the
peculiar bone called the quadrate, the bone with which the lower
jaw articulates in birds and reptiles; and certain elemental parts
of the lower jaw itself. And even these bones, in certain mammal-
like reptiles, had become mere vestiges. Even the double condyle
of the mammal skull, with which the vertebrae articulate, so like
those of the amphibian skull that Huxley based his belief of the
amphibian origin of the mammals chiefly upon it, has now been
found in certain reptiles. Warm-bloodedness, one of the diagnostic
characters of birds and mammals, is not really very important,
since it must have arisen in these two classes independently, and
we may easily conceive that the earliest mammals were cold-
blooded or that the immediate ancestors of the mammals were
warm-blooded.

It is an interesting fact in the history of the vertebrates, as of
all other ‘groups of animals and plants, that the chief divisions arose
early in geological history. Every known order of amphibians
and reptiles, unless it be that including the blind-worms, was
differentiated by the close of the Triassic period. The frogs are
now known from the Jurassic. The mammals and birds also quite
surely date their birth from the Triassic. And this early differ-
entiation of the chief groups is doubtless due to the fact that the
potentialities of diverse evolution are limited by specialization.
It is apparently a law that evolution is irreversible, that it never
goes from the special to the general, that an organism or an organ
once extinct or functionally lost never reappears. And it is also
a law in evolution that the parts in an organism tend toward
reduction in number, with the fewer parts greatly specialized in
function, just as the most perfect human machine is that which has
the fewest parts, and each part most highly adapted to the special
function it has to subserve. And these laws explain why it is that no
highly specialized organism can be ancestral to others differing widely
from it. The more radically distinct an organism is from its allies,
the earlier it must have branched off from the genealogical tree.
4 WATER REPTILES OF THE PAST AND PRESENT

The many new discoveries of extinct forms so often intermedi-
ate, not only between the larger groups, but between many of the
lesser ones as well, are making the classification of the vertebrates
increasingly difficult. At one time it was sufficient to define a
reptile as a cold-blooded animal with a single occipital condyle,
that is, with a single articular surface between the skull and the
first vertebra of the neck; a mammal as a warm-blooded animal
with two articular surfaces; but these definitions are no longer
strictly correct, Connecting links do not break down classifica-
tion, as one might think, but they do often spoil our fine systems
and compel our classifiers to take a wider view of nature than their
own narrow province affords.

We can never hope that most, or even the greater part, of all
the animals which have lived in the past will ever become known
to us, even imperfectly. Doubtless the species of the past geologi-
cal ages outnumbered many times, perhaps hundreds of times,
all those now living, since many of these latter are merely the
remnants of far more varied and extensive faunas. At times the
conditions for the preservation of the remains of animal life have
been more favorable than at others, and, under such favorable
conditions, a fairly good glimpse is sometimes given us of the fauna
of some isolated epoch and locality in the earth’s history. Those
animals which lived in and about the water have been preserved
in greater numbers and more perfectly than the strictly land
animals, since fossils are due to the preserving action of water,
with few exceptions. Of those animals which lived upon the land
or in the air only the rarest of accidents carried the skeletons into
the lakes, seas, and oceans. And, even when they had been covered
by sediments at the bottoms of lakes and seas and hidden away
from adverse agencies, it has often happened that the great erosions
of later ages have carried away and destroyed the rocks in which
they were inclosed. The records of long intervals of time have
thus been lost in all parts of the world. That we are able to obtain
even an imperfectly continuous history is due to the fact that the
intervals thus lost are not everywhere contemporaneous, that the
missing records of one place may be filled out in part elsewhere.
But this substitution of records from a distance can never make
INTRODUCTION 5

the history complete. If, in human history, we had only the
records for one century in China, for another in England, and for
yet another in South America, how imperfect indeed would be our
knowledge of human progress. Animals and plants are never quite
alike in remote regions, and they never have been. The living
reptiles of North and South America are today almost entirely
different, and, were their fossil remains to be discovered a-million
years hence, it would be very difficult to decide that they had once
lived contemporaneously; difficult, though perhaps not impossible,
since some are so nearly alike that their relationships or possible
‘identity would probably be established after long search. This
will serve to make clear how very difficult it is, for the most part,
to correlate exactly the geological formations in remote regions
of the earth, or even sometimes in adjacent regions where the fossils
are scanty, or the conditions under which the animals had lived
were very different.

There are long periods of time, millions of years at a stretch
perhaps, throughout which our knowledge amounts to little or
nothing concerning many land reptiles which we are sure must
have existed abundantly. No better example of our oftentimes
scanty knowledge can be cited than the following. Until within
the past fifteen years it was thought that true land lizards, of which,
there are about eighteen hundred species now living, dated back
‘in their history no farther than about the close of the great Second-
ary Period, or the Age of Reptiles. But a single skull of a true
land lizard has been discovered in the Triassic deposits of South
Africa, a skull of a form so nearly like that of the modern iguana .
of America that its discoverer, Dr. Broom, has called it Paliguana.
The lizards must have been in existence, probably many thousand
species of them, during all the great interval of time between
the Middle Triassic and the close of the Cretaceous, since it
is a law which can have no exception, that a type of life once
extinct never reappears. The “ancient iguanas’ of the Trias
must have been the forbears of many, if not all, of the lizards of
later times, though nothing is known of their descendants through
a period of time which can be measured only by millions of
years.
6 WATER REPTILES OF THE PAST AND PRESENT

However, notwithstanding these imperfections of our geological
records, we know very much more about extinct reptiles than we
do about living ones, so far at least as those parts capable of pres-
ervation in the rocks are concerned. Were our knowledge of
reptiles confined to the forms now living upon the earth it would
be relatively very incomplete since, aside from the lizards and
snakes, they are merely the remnants of what was once a mighty
class of vertebrates.

Not only do we learn from the remains preserved in the rocks
the precise shape and structure of the bones of the skeleton and
their precise articulations, but we are often able to determine not
a little regarding the forms which the living animals had by the
impressions made by the dead bodies in the soft sediment which
inclosed them before decomposition of the softer parts had ensued,
sediments which afterward solidified into hard rock. But these
impressions are, with rare exceptions, only those of profiles or of
flattened membranes. The rounded bodies of life do not retain
their shape long enough for the sediment to harden; in most
cases the flesh has decomposed before being entirely covered by
sediment. Sometimes the integument and scales in a carbonized
condition are actually preserved, retaining some of the actual
structure of the organized material. The carbon pigment of the
skin has sometimes been preserved in patterns indicating the color-
markings in some of these ancient reptiles; and even the micro-
scopic structure has been detected in carbonized remains of organs.
Fossil stomach contents, the bony remains of unhatched young, as
well as the delicate impressions of skin and membrane, all add to
our knowledge of the structure and habits of the animals which
lived so long ago. Many other things also may be learned, or at
least inferred, concerning the living animals and their habits from
the positions in which the skeletons are found, from the nature of
the rocks which inclose them, or from the character and abundance
of other fossils found with them. The frequent discovery of bones
which had been injured and mended during life, or the living ampu-
tation of members, often tell of the characteristics of the creatures.
So, too, the climatic conditions under which the animals lived may
often be inferred with tolerable certainty; the presence of ‘‘stomach
INTRODUCTION 7

stones’’ reveals something of the food habits, and even of the struc-
ture of the alimentary canal, etc.

All this information is gained slowly, often very slowly, and with
much labor and pains. Rarely or never is it the case that all
the information obtainable concerning any one kind of an extinct
animal is furnished by a single specimen. Skeletons are very sel-
dom, perhaps never, found quite complete, with all their parts in
their natural positions; and the nature of the matrix inclosing them
usually prevents a study of all parts of any specimen. If a newly
discovered fossil is widely different from the corresponding parts
of any creature previously known, whether living or extinct, we
cannot infer very much from a few bones as to what the remainder
of the skeleton is like. Such inferences or guesses in the past have
often resulted in grievous error, and self-respecting paleontologists
are now very reluctant to speculate much concerning extinct
animals from fragments of a skeleton, no matter what those frag-
ments or bones may be; future discoveries aré sure to reveal errors.
It is, therefore, only by the accumulation of much, material, and
by the careful study and comparison of all known related ‘animals,
that reliable conclusions can be reached. Often it requires scores
of specimens to determine the exact structure of a single kind of
animal, and, as the collection and preparation of fossil skeletons
are tedious and expensive, our knowledge sometimes increases
very slowly. In recent years, however, there have been many more
students of extinct backboned animals than formerly, and there
are now many museums and universities which spend annually
large sums of money in the collection and preparation of such fos-
sils. This greater activity of the last twenty years is bringing to
light many new and strange forms, as well as completing our
knowledge of those previously imperfectly known.

It is commonly, but erroneously, believed that the bones of
extinct animals are usually found in excavations made for the pur-
pose. It is true that not a few specimens of fossils have been
discovered in excavations made for other purposes, such as
railway cuttings, quarries, wells, etc., but if no others were found
our knowledge of the animals of the past would be very meager
indeed. Fossils are, for the most part, found by deliberate search
8 WATER REPTILES OF THE PAST AND PRESENT

over the denuded rocks in which they occur. Methods of search
and collection will best be understood by the following description
of the noted fossil-bearing rocks of western Kansas.

About the middle of Cretaceous times, there extended from the
Gulf of Mexico on the south to or nearly to the Arctic Ocean on
the north a narrow inland ocean or sea, a few hundred miles in
width, covering what is now the western part of Kansas and the
eastern part of Colorado, and separating the North American

 

 

 

Fic. 1.—A characteristic chalk exposure in western Kansas, a hundred acres or
more in extent.

continent into two distinct bodies of land. This ocean, because of
its location, bordered on both sides by low-lying lands—the Rocky
Mountains had not then been pushed up—doubtless was compara-
tively calm and placid, free from violent storms and high tides.
That the climate, in the region of Kansas at least, was warm or
even subtropical is fairly certain, since plants allied to those now
living in warm, temperate, or subtropical regions were then living
much farther to the north; and since the animals which then
INTRODUCTION 9

lived in this sea were only such as would be expected in waters of
warm temperature. Its tributary rivers could have been neither
large nor swift-flowing, since the sediment at its bottom was free,
or nearly free, from in-brought material. This was at least the
case not very far from its shores. Its slowly falling sediment was
composed, almost exclusively, of microscopic shells of animals
and plants, foraminifera and coccoliths. The deposits thus made
are almost identical with those now forming in various parts of
the world in clear but not deep waters, away from the immediate
coasts of the continents, almost pure chalk. Animals dying in
this inland sea fell slowly to the bottom during or after decomposi-
tion of their softer parts, and the slowly increasing sediments
covered up and buried the preservable parts. The many preda-
ceous fishes and other scavengers with which the waters abounded
often tore the decomposing bodies apart, separating and displacing
the bones of the skeleton; and the currents of the shallow waters
washed others apart. Often the teeth of fishes and other carnivorous
animals are found imbedded in the bones, and many are the scars
and toothmarks observed in the fossil bones.

After the ocean had dried up and the bottom had been raised
far above the present level of the oceans, other deposits made in
lakes and by the winds covered deeply the consolidating sediments,
burying them for millions of years with all that they contained.
Long-continued erosion by winds and rains has again laid bare
many parts of the old ocean bottom, and has washed them out
into ravines and gullies. Many hundreds of square miles of this
chalk are now laid bare in western Kansas, upon which the growth
of vegetation has been prevented by the arid climate. Here and
there may now be discovered protruding from the sloping or pre-
cipitous surfaces of this exposed chalk bones or parts of bones of
the old animals buried so long ago in the soft sediment of the ancient
ocean bottom.

The sharp-eyed searcher after fossils detects these protruding,
often broken and weather-worn, petrified bones, which themselves
betray the presence often of other parts of their skeletons still
concealed in the chalky hillside. Fortunate is he if he has dis-
covered a specimen soon after it appeared at the surface, before
Io WATER REPTILES OF THE PAST AND PRESENT

the rains have washed away and destroyed most of the remains
that had been there preserved. Still more fortunate is he if all
or nearly all of the original skeleton has been preserved together
in its natural relations. After days, perhaps weeks, of labor, the
specimen is secured and shipped to the laboratory. Those parts
which have been washed out of the chalky rock before the dis-
covery of the specimen are always more or less injured and for the
most part lost, their fragments strewn down the hillside, for erosion
is always slow and many years may have elapsed since first the
specimen had appeared at the surface. More frequently, perhaps,
a few strokes of the pick and shovel disclose but one, two, or three
bones remaining in the rocks. The specimen, if large, or composed
of many bones, is carefully uncovered sufficiently to show its.extent,
and then, so far as possible, removed in large blocks of the rock.
The bones themselves, notwithstanding their petrifaction, are
usually soft and easily broken, and their separate removal from the
matrix may require weeks or even months of labor, work which
cannot be done prudently in the field.

Of many specimens the rock matrix is so hard that the task of
removing it from the bones is slow and difficult, indeed well-nigh
impossible, for the bones are usually softer than their surrounding
matrix. On the other hand, the matrix may be so soft and friable
that it cannot be quarried out in blocks. In such cases the separate
divisions, as. large as they can be excavated and safely handled,
are carefully covered with thick bandages of burlap and plaster-of-
paris, often strengthened with rods of iron or boards. The skeleton
of a single animal treated in this way may require weeks and even
months to collect, prepare, and mount in the museum.

From what has been said the reader will understand how it is
possible to make an approximately accurate picture of extinct
animals as they appeared in life—approximately accurate, never
absolutely so. The flesh and other soft parts of an animal are
never petrified, though it is a common belief that they may be.
Petrified men and women are still occasionally shown in cheap
museums, but they are always frauds. Many times has the writer
been called upon to express an opinion as to the nature of some con-
cretion which the discoverer was sure was a petrified snake, turtle,
INTRODUCTION II

or even some part of the human body, because of fancied resem-
blances in shape and size. Not too emphatically can it be said
that anything dug from the earth having the shape of a living ani-
mal and alleged to be petrified is either an accidental resemblance
or a deliberate humbug—if we except such extraordinary casts as
those of Pompeii. The Cardiff Giant and the Muldoon are still
fresh in the memory of some of us. There have been a few instances
where flesh has been preserved in the North, frozen for thousands

 

 

 

Fic. 2.—Removing a specimen of fish in a block from the chalk of western Kansas

of years, but frozen fossils are very different from petrified fossils.
Flesh decays before it possibly can be petrified, and only rarely
is the residue of flesh, tendons, and skin, that is, the carbon and
mineral matters, preserved.

One may sometimes restore extinct animals as in life, knowing
fully the shape and structure of the skeleton, and still be far from
the rea] truth. All elephants of the present time have a bare or
nearly bare skin. If all that we knew of the extinct mammoth
were derived from the skeleton we should never have suspected
12 WATER REPTILES OF THE PAST AND PRESENT

that the creature was clothed during life with long and abundant
hair, such as has been found with the frozen bodies in Siberia.
Nor should we suspect that the dromedary and Bactrian camels of
today have large masses of fat on their backs, if we knew only their
skeletons. It must therefore be remembered that al] restorations’
of extinct animals, representing them as in life, are merely the sum
of our knowledge concerning them, as close approximations to the
real truth as it is possible to make. Or, rather, they should be
such approximations; unfortunately many such restorations have
been made by artists wholly unacquainted with the anatomy of the
creatures they attempt to represent, often adorned with appendages
drawn from a too vivid imagination.
CHAPTER II
CLASSIFICATION OF REPTILES

There is very much doubt, very much uncertainty, among
paleontologists about the classification of reptiles. No two writers
agree on the number of orders, or the rank of many forms. Some
recognize twenty or more orders, others but eight or nine. And
this doubt and uncertainty are due chiefly to the many discoveries
of early forms that have been made during the past twenty
years. The many strange and unclassifiable types which have
come to light in North America, South Africa, and Europe have
thrown doubt on all previous classificatory schemes, have weakened
our faith in all attempts to trace out the genealogies of the reptil-
ian orders; and classification is merely genealogy. It is only the
paleontologist who is competent to express opinions concerning the
larger principles of classification of organisms, and especially of
the classification of reptiles. The neozodlogist, ignorant of extinct
forms, can only hazard guesses and conjectures as to the relation-
ships of the larger groups, for he has only the specialized or decadent
remnants of past faunas upon which to base his opinions. About
some things we can be quite confident; about some groups opin-
ions have crystallized, and we all agree, except perhaps on trifles.
The dinosaurs, the pterodactyls, the crocodiles, for instance, offer
only minor problems to perplex the systematist, but the origin
and the relations, not only of these, but also of nearly all the others,
are still involved in obscurity. The question, whence came the
ichthyosaurs, the plesiosaurs, the turtles, etc., seems almost as far
from solution as it did fifty years ago. With every problem solved
a dozen more intrude themselves upon us. Hence, classification
simply represents the present condition of our knowledge, our
present opinions as to genealogies. It was the fashion a dozen
years ago to draw all sorts of genealogical trees on the slightest
pretext, to trace in beautifully clear lines the precise descent of all
kinds of animals; and very few have been worth the paper on

13
14 WATER REPTILES OF THE PAST AND PRESENT

which they were printed. When facts are numerous enough, con-
clusions are patent even to the novice; when facts are few and
obscure, one can guess about as well as another. In general, it may
be said that the older a group of animals is the more abstruse are
the problems presented; first, because of the Jack of abundant
material; second, because the forms speak to us in an unfamiliar
language that we cannot easily interpret. The classification of the
mammals approaches more nearly the ultimate truth than does that
of any other group of organisms, because we know more about the
extinct forms than we do of any other class, and also because we
know more about the living forms than we do about any other
living animals.

Species of reptiles are, for the most part, vague quantities in
paleontology; they can be determined with assurance only by the
comparison of abundant material. Adult characters in mammals
are apparent in the ossification of the skeleton, and size can be used
within moderate limits in the determination of species; but size
in. reptiles means but little; no one could possibly say that the
skeleton of an alligator six feet in length is not that of an adult
animal if he knew nothing else about the Crocodilia. So also the
compression and malformations of bones from the processes of
fossilization obliterate specific characters in great part. Nor are
specific characters easily distinguishable in the skeletons of living
reptiles. The genus, therefore, among fossil reptiles is practically
the unit, and we may be sure that for every well-defined genus we
discover there existed numerous minor variations, which, had we
the living animals to study, we should call species. We classify
the living Crocodilia into two families, about four well-defined
genera—perhaps even five or. six—and about twenty-five species.
Of the living lizards there are about eighteen hundred species,
twenty families, and four larger groups or suborders. In all
probability the lizards have never been more abundant and more
varied than they are at the present time. Possibly these propor-
tions of species, genera, families, and suborders may represent
approximately the proportions that have existed at some time or
other in most of the other groups which we call orders—approxi-
mately only, for we can never be quite sure that we evaluate the
CLASSIFICATION OF REPTILES 15

structural characters of different groups of organisms quite equally.
The absence of a molar tooth in a mammal would ordinarily indicate
a genus, the absence of a tooth in a reptile might not indicate even a
variety or a race. Whence it follows that classification of organ-
isms is not and never will be an exact science. The value of char-
acters used in classification is very unequal, as we have seen. No
two persons see these characters from the same viewpoints, and in
consequence no two persons whose opinions are worth while ever
wholly agree as to classification.

The following scheme differs only in minor details from the
more conservative of the. generally accepted views, and those
differences are, for the most part, the writer’s own opinions, to be
taken for what they are worth. It may be said decisively that
no classification of the reptiles into major groups, into super-
families or subclasses that has so far been proposed is worthy of
acceptance; there is no such subclass as the Diapsida or Synapsida,
for instance. And we have very much more to learn about the
early reptiles before any general classification of the reptiles can be
securely founded. It is very probable that the primary radiation of
the reptiles into the various lines of descent, into its main branches,
occurred much earlier than we have been disposed to believe;. that
before the close of Paleozoic time, perhaps before the close of the
Carboniferous, all the great groups of reptiles had gone off from the
main stem, and that since then only smaller and smaller branches
have appeared. There have been no new orders of reptiles in all
probability since Triassic times, and perhaps none since Permian.

Taxonomists are often disposed to cut the Gordian knots of
relationships by raising the ranks of the animals they study to
independent positions. More than thirty independent orders of
reptiles have been proposed by different students, and quite as
many of mammals and of birds; possibly after more forms have
been discovered there will be as many proposed for the amphibians.
Sometimes, indeed, it is better to make such independent groups
than to unite lesser ones on doubtful evidence. But the writer,
for one, believes that it is more worthy of the thoughtful scientific
student to seek for relationships than for differences. It is far
easier to destroy than to construct, to make new genera, families,
*

16 WATER REPTILES OF THE PAST AND PRESENT

and orders than to unite those already proposed. To raise every
proposed suborder of reptiles to an order, as has been proposed
by various writers, and the orders to subclasses, only leaves classi-
fication where it was; nothing has been added to taxonomy save
a lot of new names to perplex and annoy the student.

In the following scheme of classification three groups provision-
ally called orders are prefixed by an asterisk.

CLASS REPTILIA

Order COTYLOSAURIA
Primitive reptiles with notochordal vertebrae, imperforate temporal region,
persistent intercentra; two coracoids; plate-like pelvis, with all or most
of the amphibian skull elements; short legs’and short neck; phalangeal
formula primarily 2, 3, 4, 5, 3(4).
Suborder Diadectosauria Permocarboniferous, North America.

Pantylosauria Permocarboniferous, North America.
Labidosauria Lower Permian, North America.
Pareiasauria Upper Permian, Europe, Africa.

Procolophonia Triassic, Europe, Africa.
Order CHELONIA
Temporal region imperforate. Head and limbs more or less retractile
within a box formed chiefly by the exoskeleton.
Suborder Pleurodira Triassic to recent.
Cryptodira Jurassic to recent.
Trionychoidea Cretaceous to recent.
Order THEROMORPHA
Primitive reptiles with notochordal vertebrae, perforate temporal region,
persistent intercentra; two coracoids; plate-like pelvis with median vacu-
ity; no free dermosupraoccipitals in skull; longer legs and neck; phalangeal
formula 2, 3, 4, 5, 3(4).
Suborder Pelycosauria (sens. Jat.) Permocarboniferous, North America,

Europe. arth yh
Dromasauria Upper Permian, Africa.
Dinocephalia Middle and Upper Permian, Africa.

Order THERAPSIDA
Reptiles with a single temporal perforation on each side; vertebrae not
notochordal; intercentra not persistent; pelvis with vacuity; skull bones
reduced; teeth heterodont; phalangeal formula, 2, 3, 3, 3, 3.
Suborder Anomodontia Permo-Trias, Africa, North America.
Therocephalia Upper Permian, Africa.

¥ Theriodontia Trias, Africa.
CLASSIFICATION OF REPTILES 17

Order SAUROPTERYGIA
Aquatic reptiles with a single temporal vacuity; no supratemporal bone,
or quadratojugal; ribs single-headed, diapophysial; coracoids large, meet-
ing in middle line, single; neck long, tail short.

Suborder Nothosauria Triassic, Europe.
Plesiosauria Triassic to close of Cretaceous, cosmopolitan.

*Order PROGANOSAURIA
Primitive aquatic reptiles; single (? upper) temporal perforation; neck
elongate; nares posterior; vertebrae notochordal; intercentra persistent;
pelvis plate-like; phalangeal formula 2, 3, 4, 5, 4(6). Permocarboniferous,
Africa, South America.

Order ICHTHYOSAURIA
Reptiles with all aquatic adaptations; a single, upper temporal perfora-
tion; both supratemporal and squamosal present; a single coracoid.
Middle Triassic to Benton Cretaceous, cosmopolitan.

*Order PROTOROSAURIA
Asingle, upper temporal vacuity, quadrate fixed (neck vertebrae elongate) ;
bones hollow; cervical ribs single-headed, articulating with centrum;
pelvis plate-like. Permian, North America, Europe.

Order SQUAMATA
A single, upper temporal vacuity; or, secondarily none; quadrate loosely
articulated with cranium; teeth on palate; intercentra more or less per-
sistent; a single coracoid; ribs single-headed, central.

Suborder Lacertilia Trias to recent.
Mosasauria Upper Cretaceous, cosmopolitan.
Ophidia Upper Cretaceous to recent.

*Order THALATTOSAURIA
Aquatic reptiles; two (?) temporal vacuities; ribs single-headed, attached
to centrum; single coracoid; no intercentra. Trias, California.

Order RHYNCHOCEPHALIA
Two temporal vacuities on each side; palate with teeth; intercentra
persistent; a single coracoid; teeth acrodont; ribs articulating with
centrum and arch.

Suborder Rhynchosauria Triassic, Europe.
Sphenodontia Triassic to recent.
Choristodera Uppermost Cretaceous, lowermost Eocene,
North America, Europe.
18 WATER REPTILES OF THE PAST AND PRESENT

Order PARASUCHIA
Subaquatic reptiles, with two temporal vacuities; an antorbital vacuity;
no false palate; pubis entering acetabulum; ribs double-headed, diapo-
physial. :
Suborder Phytosauria Upper Trias, cosmopolitan. G. lod pes
Pelycosimia Trias, Africa.
Pseudosuchia Trias, Europe, North America.

Order CROCODILIA
Two temporal vacuities; teeth thecodont; a false palate; pubis excluded
from acetabulum; single coracoid; ribs double-headed, diapophysial;
subaquatie or aquatic. é
Suborder Eusuchia Jurassic to recent.
Thalattosuchia Upper Jurassic, Europe.

Order DINOSAURIA
Ambulatory reptiles, with two temporal vacuities; no false palate; pubis
entering acetabulum; ribs double-headed, diapophysial.
Suborder Theropoda Upper Trias to close of Cretaceous, cosmopolitan.
Orthopoda _ Close of Trias to close of Cretaceous, cosmopolitan.
Sauropoda Upper Jurassic, Lower Cretaceous, cosmopolitan.

Order PTEROSAURIA

‘Volant reptiles; fourth finger greatly elongated to support patagium;
neck vertebrae elongated; bones hollow; ribs double-headed, diapo-
physial; a single coracoid; no clavicles or interclavicle; two temporal
vacuities. :
Suborder Pterodermata Jurassic, Europe.

Pterodactyloidea Upper Jurassic to Upper Cretaceous, Europe,
North America.
CHAPTER III
THE SKELETON OF REPTILES

The bony framework, or skeleton, that which gives form and
stature to the body, and which serves for the support of the soft
parts and the attachment of muscles, is, with rare exceptions, all
that is ever preserved of fossil animals. Because, therefore, .
students of extinct animals must rely so much, if not exclusively,
upon the skeleton much attention has been given to the study of
comparative osteology, the science of bones. Not only are most
of the bones of the skeleton characteristic of the genus to which
they belong, but the more general plan of the skeleton, or parts
of the skeleton, is likewise characteristic of the larger groups. The
paleontologist may become so expert in deciphering the characters
of single bones, or even parts of bones—often all that are known
of animals new to science—that he is able to hazard guesses as to
the general structure of the skeleton to which they belong. But
such guesses usually will approximate the real truth only in the
degree that the bones upon which they are based approximate
‘like bones of other animals that are better known. Not all parts
of the skeleton are equally characteristic of the type of animal which
possessed them. A tooth of a mammal may positively determine
the species to which it belongs, while the toe bone of the same
animal might not enable one to guess at its family, even. As a
rule one can seldom be quite sure of the species of a reptile unless
the larger part of the skeleton, or at least the skull, is available,
although almost any bone of the skeleton, if one is expert, will
permit a decision as to the family, if not the genus.

One must often depend upon the positions and relations of the
bones, as found in the rocky matrix, for the final determination
of many characters. One can, for instance, never be sure of the
number of bones in the neck, trunk, tail, or feet of a reptile, until
specimens have been found with all such bones in position. It
is for this reason that much care is exercised in the collection of

19
20 WATER REPTILES OF THE PAST AND PRESENT

|
’ specimens of fossil animals, and especially
of fossil reptiles, to preserve all parts of
the skeleton, so far as possible, in the
relations they occupied in the rocks until
they can be studied in the laboratory.
Many grievous errors have been made in

 

RRR aR RMR

the past by hasty inferences from fragmen-

tary and poorly collected specimens.
Because of the reliance which must be
placed upon the skeleton it will be neces-
sary to speak somewhat in detail of its
structure in the reptiles, and to use not
7 a few terms in its description that are
S unfamiliar to the general reader. So far as
a) possible technical terms will be avoided,
Ee though some must be used, as there are

  
  
  

 

no equivalents in the English language
for them. The reader may use this

fj | y chapter as a sort of explanatory index
py ivan vite é *.

A cer NE or glossary for the better elucidation of

1 gee the necessary details of the following

chapters.

It is needless to say that the skeleton of
a reptile is arranged on essentially the
same plan as that of our own; the bones
have the same names that they have in
our own skeleton, but there are more of
them, and the individual bones, as a
general rule, are Jess highly specialized,
that is, are not so well adapted for special
functions. In a word, the skeleton of a
reptile for the mest part is generalized,
though particular parts may be highly
specialized for particular uses. As a rule,
if not as a law, the course of evolution
has been to reduce the number of parts
‘and to adapt those which remain more

<——
a=
9
Fic. 3.—Limnoscelis, a subaquatic cotylosaur, from the Permocarboniferous of New Mexico

 
THE SKELETON OF REPTILES 21

closely to their special uses, either by increase in size, or by modifi-
cations of their shape and structure.

SKULL AND TEETH

The skull of reptiles is much more primitive or generalized in
structure than is that of mammals, to such an extent, indeed, that
there is yet much doubt as to the precise homologies of some of the
bones composing it; and, inasmuch as the names were originally
given, for the most part, to the bones of the human skull, there is
still some confusion among students as to the proper names in
all cases, a confusion that doubt-
less will not be wholly dissipated
until we know much more about
the early or more primitive
reptiles than we do at present.

 

Fic. 5

 

Fic. 4.—Seymouria, a primitive cotylosaurian. Skull, from above: pm, pre-
maxilla; », nasal; /, lacrimal; », prefrontal; /, frontal; pf, postfrontal; it, inter-
temporal; st, supratemporal; sg, squamosal; ds, dermosupraoccipital; #, tabulare;
j, jugal; po, postorbital; m, maxilla; s, surangular; amg, angular; pa, parietal.

Fic. 5.—Seymouria, skull from the side. Explanations as in fig. 4.

As in other parts of the skeleton, there has been a reduction
in the number of parts of the reptile skull from that of the more
primitive forms, and a better adaptation of those which remain
for the special uses they subserve. This reduction in number has
been caused in part by the actual loss of bones, in part by the fusion
of contiguous ones. The most primitive reptiles had no less than
seventy-two separate bones in the skull;t the human skull has

t Paired maxillae, premaxillae, nasals, prefrontals, lacrimals, frontals, parietals,
dermosupraoccipitals, tabularia, supratemporals, intertemporals, squamosals, jugals, '
quadratojugals, postorbitals, postfrontals, quadrates, exoccipitals, paroccipitals,
vomers, palatines, pterygoids, sphenomaxillae, stapes, transverse, alisphenoids or
orbitosphenoids, epipterygoids, articulars, prearticulars, angulars, surangulars, coro-
noids, splenials, dentaries, one supraoccipital, one basioccipital, one basisphenoid,
one ethmoid.
22 WATER REPTILES OF THE PAST AND PRESENT

but twenty-eight inclusive of the ear bones. There is but little
variation, either in the number or in the relations of bones, in the
mammalian skull. If one knows the human skull thoroughly he
can easily understand the structure of the skull of any mammal.
The same cannot be said of the skulls of reptiles; one would be
greatly puzzled in the comparison of the skulls of turtles and croco-
diles, if he knew nothing about other forms. And it is safe to
formulate another general law in evolution here: Characters which
have been. longest inherited are
least liable to change. The earliest
reptiles had at least four pairs of
bones which have disappeared in
all later reptiles; and they had
some bones in pairs which have
fused in later reptiles, either with
their mates or with contiguous
bones. The crocodile has at least
two pairs of bones which have
disappeared in turtles. On the
other hand, the turtle has at least
one pair of free bones which have
been fused with adjacent bones in
the crocodiles, and one pair that

 

Fic. 6.—Labidosaurus, a cotylosaur.
Skull from above: pm, premaxilla; n, ori .
nasal; m, maxilla; J, lacrimal; , pre- is fused which is free in the latter.

frontal; fr, frontal; pf, postfrontal; The lizard has one pair of bones

ital; 7, jugal; ietal; 7 ‘
pe peroital J, ugals Pa, Pariet@s that has been wholly wanting in
sq, squamosal; ds, dermosupraoccipi-

tal; pf, parietal foramen. other reptiles for millions of years,

while on the other hand it has lost
some bones that are present in all other modern reptiles. The
four parts of the occipital bone of mammals, basioccipital, exoccipi-
tals, and supraoccipital, are almost invariably free and there is a
single occipital condyle, except in the Theriodontia.

In this reduction or fusion of parts, or in addition thereto, there
has been a general lightening-up of the whole skull-structure in
reptiles from the rather massive and protected form of the older
to the lighter, less protected, and more fragile type of the
later ones, since speed, greater agility, better sense organs, and
THE SKELETON OF REPTILES : 23

doubtless greater brain power have rendered unnecessary or useless
the older kinds, just as modern methods and modern arms have
rendered useless the coat of mail of the Middle Ages.

The old reptiles had a continuous covering or roof for the skull,
pierced only by the openings for the nostrils in front—the nares—
the orbits for the eyes near the middle, and a smaller median open-
ing back of them for the so-called ‘‘pineal eye.”” The temporal
region, that is, the region back of the orbits on each side, was
completely roofed over by bone for the support and protection of
the jaw muscles. In later reptiles this region has been lightened,

   

Fic. 7.—Edaphosaurus, a theromorph reptile from the Permian of Texas. Skull
with single temporal vacuity.

either by holes that pierce it or by the emargination of its free
borders, as in the turtles. The openings have occurred in different
ways, and with the loss of different bones in various lines of descent.
In one large group of reptiles, comprising the pterodactyls, dino-
saurs, phytosaurs, crocodiles, and rhynchocephalians, there are
two openings on each side, called the supratemporal and lateral
temporal vacuities. In another still larger group there is a single
vacuity on each side, all members of which it has been thought were
markedly related to each other. Some of these, the lizards, snakes,
and mosasaurs, the ichthyosaurs, and probably the proganosaurs,
24 WATER REPTILES OF THE PAST AND PRESENT

have the single opening high up on the side, corresponding
apparently to the supratemporal vacuity of the double-arched
forms, as those with two openings are called. Many others, how-
ever, like the whole order Therapsida and the Theromorpha, have
the single opening lower down and bounded differently; their
relationships are doubtful, since it is very much of a question how
the single opening has arisen. There have been many theories
to account for the origin of the temporal vacuities, but all are yet
speculations. Notwithstanding these doubts, which more recent
discoveries have intensified, there can be none that the structure

 

Fic. 8.—Sphenodon (tuatera), Skull from side and above: pm, premaxilla;
n, nasal; prf, prefrontal; f, frontal; pf, postfrontal; », parietal; po, postorbital;
sq, squamosal; m, maxilla; 7, jugal; qj, quadratojugal; g, quadrate; c, coronoid;
sa, surangular; art, articular; pa, prearticular; d, dentary; an, angular.

of this region of the skull offers important and reliable characters
for the classification of the reptiles into the larger groups, but,
unfortunately, we are very uncertain yet as to what this classi-
fication should be. We are confident that all those reptiles having
two temporal vacuities on each side are related to each other; we
are yet very much in doubt as to the classification of a]] other
reptiles, or at least all others having only a single temporal vacuity
on each side.

Better evidences of relationships, or the absence of relation-
ships, are offered by the presence of certain bones in the skulls
in some orders that are lost in others, since it may be accepted as
THE SKELETON OF REPTILES 25

an axiom that new bones have not appeared in the skulls of reptiles,
birds, or mammals; and that no bone which has once disappeared
has ever been functionally regained by the descendants of those
that lost it. The presence, then, of an extra bone in the temporal
region of the lizards or the ichthyosaurs is proof that they have had
a long and independent descent from reptiles which possessed it.

The mandible of the earliest reptiles was composed of not less
than seven separate and distinct bones, as shown in the accom-
panying figures. The mandible of no modern reptile has more
than six, and some have fewer. The mandible of mammals is
composed of a single bone, the dentary; those reptiles, the Therio-
dontia, which doubtless were ancestral to the mammals in Triassic
times, have all the bones, except the dentary, much reduced, or
even vestigial. The prearticular bone, as shown, so far as known,
has been absent in all reptiles since Triassic times, except the
ichthyosaurs, plesiosaurs, Sphenodon, and turtles, al]l reptiles of
ancient origin. The coronoid bone primitively extended the whole
length of the teeth on the inner side; in all reptiles, except the
plesiosaurs, since Triassic times it is either reduced to a small bone
back of the teeth or is absent. So also the splenial has been greatly
reduced in size in all later reptiles and may be wanting as in
Sphenodon and modern turtles. The articular of reptiles, it is now
generally believed, is represented in mammals by one of the ear
bones, the quadrate by another.

The teeth of reptiles are of much less importance, as a rule, in
the determination of relationships than are the teeth of mammals.
Rarely are their shapes of specific, and often not of generic, impor-
tance, though their number and relative sizes may be. The teeth
of mammals, as a rule, are forty-four or less in number, and they
are always inserted in distinct sockets in the jaw bones. Among
reptiles they are indefinite in number, and may be attached to ©
any of the bones of the palate and sometimes also to the coronoid
of the mandibles. Furthermore, except in those reptiles related
to the immediate ancestors of the mammals, they are alike or
nearly alike in the jaws, that is, homodont, not distinguishable
into incisors, canines, and molars. They may be inserted in
separate sockets (thecodont), in grooves, or simply be co-ossified
26 WATER REPTILES OF THE PAST AND PRESENT

   

an E

Fic. 9.—Mandible of Trimerorhachis, a stegocephalian amphibian, ancestrally
related to the reptiles: A from within; B from without. The coronoid is composed
of three bones, the true coronoid (cor), the intercoronoid (icor), and the precoronoid
(pc). The splenial is composed of two, the true splenial (sp) and the postsplenial
(psp). The prearticular (pa) is broad, the dentary (d) is small; and the angular (an)
is only slightly visible on the inner side.

 

Fic. 10.—Mandible of Labidosaurus, a cotylosaur reptile: A from within; B from
without. The coronoid (cor) is a single bone, but extends far forward. The splenial
(sp) is also a single bone, replacing the two of the amphibians. The prearticular (pa)
is narrower, and the angular (ang) appears broadly on the inner side. The dentary (d)
is much larger and the surangular (sa) is distinct. The articular (art) is small.
THE SKELETON. OF REPTILES 27

to the surface of the bone (acrodont). And they are usually
reproduced indefinitely by new teeth growing at the side of the
base or below them. More usually they
are pointed and curved; sometimes they
are flattened, with sharp cutting edges
in front and behind in the more strictly
carnivorous reptiles; in those of her-
bivorous habits they are more dilated
and roughened on the crown, not
pointed; in not a few they are low,
broad, and flat and are used only for
crushing the hard shells of invertebrates.
With the very few exceptions among
certain dinosaurs, they never have more
than one root for attachment. The
evolutional tendency for reptiles, as for
the mammals, is to loose teeth, especially
those of the palate. Among living rep-
tiles it is only the most primitive types,
such as the lizards, snakes, and the
tuatera, which have teeth on the palatal
bones, and in none are there teeth on
the vomers, as was the rule in the ancient
reptiles. The lizards may have them on
pterygoids and palatines, and the tuatera
has them on the palatines only. There
may be as many as eighty on each
jaw, above and below, and hundreds of
smaller ones on the palate, or they may
be reduced in number to five or six, or
even to a single one; some reptiles, like
the turtles and later pterodactyls, have
none. The teeth of reptiles are com-
posed of the same kinds of tissues as
are the teeth of mammals, that is, of
dentine and enamel, but the enamel is always thin, perhaps because
the teeth are so easily replaced that.a thicker protective covering

The dentary (d) has become the chief bone of the mandible.

Fic. 11.—Mandible of Alligator, a modern, highly specialized reptile, from within. The coronoid (cor) is small
and is situated far back; the splenial (sp) does not extend to the symphysis; the prearticular (pa) has disappeared,

or has fused with the angular (am) or articular (art).

 
28 WATER REPTILES OF THE PAST AND PRESENT

is not needed. The arrangement of the dentine in primitive reptiles
is complicated, that is, plicated or folded in labyrinthine figures,
like that of many stegocephalian amphibians, the Labyrinthodontia,
especially. This labyrinthine structure of the dentine persisted
longest in the ichthyosaurs.

VERTEBRAE AND RIBS

The spinal column or backbone of reptiles, as in all air-breathing
vertebrates, is made up of a variable number of separate segments
called vertebrae, permitting flexibility. Each vertebra is com-
posed of a body, or centrum, and an arch on the dorsal side for
the protection of the spinal cord. Various projections from the
vertebra, called processes, serve for the attachment of ligaments

 

Fic. 12.—Procoelous vertebra of snake: za, zygantrum; zs, zygosphene; 2, pos-
terior zygapophysis. :

or muscles, for articular union with adjacent vertebrae, or for the
support of ribs, and these processes have characteristic differences
in different reptiles. The pair in front and behind, for articulation
with the adjoining vertebrae, may become obsolete or even lost in
swimming reptiles, as we shall see; they are called zygapophyses.
In not a few reptiles there is an additional pair for zygapophysial
articulation in front and behind, called zygosphene and zygantrum,
for the greater strengthening of the column; they are especially
characteristic of snakes and certain lizards. In certain other.
reptiles, especially the long-necked dinosaurs, there is an addi-
tional pair arranged differently from the zygophene, that have
received the names hyposphene and hypantrum.

On the top of the arch is the spine or spinous process, which
may vary enormously in size and length; sometimes it is flattened
THE SKELETON OF REPTILES 29

or dilated above for the support of an exoskeleton, or it may be
heavy and massive for the attachment of strong muscles and liga-
ments. In the modern basilisk lizards and in the ancient Dime-
trodon and Edaphosaurus from the Permian rocks of Texas these
spines are of enormous length, some of them nearly four feet long in
reptiles not twice that length. Slender crawling reptiles usually
have no spines, or only vestigial ones. On the sides of the arch
there may be a distinct transverse process for the articulation of
the rib. |

In all early reptiles the ends of the body or centrum are concave,
as they are in nearly all fishes. Such a conformation, ca]led amphi-
coelous, gives great flexibility to the spinal column, but only
moderate strength, since the intervening spaces are filled with
cartilage in life. In all living reptiles, with few exceptions, the
body is concave, like a saucer, in front and correspondingly convex
behind, and the intervening cartilage has largely disappeared.
Such a mode of union, called procoelous, adds greatly to the strength
of the backbone, enabling it to receive greater shocks or greater
pressure without dislocation; or to sustain the greater strain of
muscles used in running swiftly or in climbing. Among living
reptiles, only the gecko lizards and the tuatera have biconcave
vertebrae. Some extinct reptiles, such as some of the dinosaurs,
animals that walked erect upon their legs, had their vertebrae
convex in front and concave behind (opisthocoelous). Birds,
though walking erect, have a very different and more complicated
articulation of the cervical vertebrae, and certain reptiles, like the
turtles, have very complicated cervical vertebrae.

In the embryos of all vertebrate animals there appears first
an elongated fibrous rod, called the notochord, in the place of the
future spinal column. This rod may persist through life, never
ossifying, as was the case with all the earliest fishes, and is the
condition in some living ones. As the embryo grows, however,
the separate segments, or vertebrae, ossify about this rod in all
reptiles, forming bony rings, perforate at first in the middle for
the more or less constricted notochord. This stage was the
permanent condition in all the earliest reptiles and in some later
ones. Such animals are said to have notochordal vertebrae, the
30 WATER REPTILES OF THE PAST AND PRESENT

notochord more or less continuous, like a string of beads, the beads
representing the enlargements between the contiguous vertebrae.

In many early amphibians, and probably in all the earliest ones,
as well as in the fishes from which they were derived, the vertebra
is more complicated in that it is composed of at least three pairs
of separate bones, two of which united with each other, the third
finally disappearing in modern animals, or at the most represented
by a mere vestige called the intercentrum. The dorsal pair of
these bones, called the neurocentra, forms the arch of the vertebra.
The ventral posterior pair, called the pleurocentra, increases in

 

Fic. 13.—Notochordal cervical vertebrae, with intercentra, of Ophiacodon, a
primitive theromorph reptile from the Permocarboniferous of New Mexico: pa, pro-
atlas; am, arch of atlas; v, odontoid; az, axis. :

size and unites to form the centrum or body of the vertebra; while
the ventral anterior pair, early united with each other, is called the
hypocentrum or intercentrum, persistent in all early reptiles as
a vestige between the centra on the ventral side. This divided
condition of the vertebra is persistent in the first vertebra, the
atlas of all higher animals, in which the so-called body is the
hypocentrum or intercentrum, the arch is the neurocentrum,
while the pleurocentra have fused more or less with the anterior
part of the next vertebra, the axis, to form the so-called odontoid.
That this is the real explanation of the structure of the atlas
THE SKELETON OF REPTILES 31

is proved by the various stages of its evolution in the reptiles,
from the earliest (Fig. 15) in which it scarcely differs from
rhachitomous—as this structure is called—vertebrae of an early
amphibian, to the modern in which the structure is nearly like
that of mammals.

In front of the atlas, that is, between it and the skull, there
was, in all early reptiles, as well as in some later ones, like the
crocodiles and tuatera, the remnant of
what is believed to have been another
vertebra, of which only the arch re-
mains, and which is called the proatlas.
In its earliest condition it articulated
with the skull in front and the arch of
the atlas behind.

As in mammals, the vertebrae of: the
different regions have received distinc-
tive names, cervical, dorsal, lumbar,
sacral, and caudal. The numbers of
each region are far more variable than
they are among mammals, the total
number of vertebrae in the column
varying from about thirty to more than
five hundred, in certain snakes. Nor
are the different regions always easily = Fic. 14—Rhachitomous
distinguishable, especially those in front  40rsal vertebra of Eryops: n,

: 5 3 neurocentrum or arch; i,
of the sacrum. In the earliest reptiles slearecentoum: 4, dnter
there was practically no neck, and only centrum or hypocentrum; az,
two vertebrae, the atlas and axis, that anterior zygapophysis; pz, pos-
properly can be called cervical. Very icity Nera eres
soon, however, the reptiles developed a _ parapophysis, for head of rib.
longer neck with seven vertebrae, a ;
number that has remained singularly constant in higher animals,
especially in the mammals. In most modern reptiles there are
from seven to nine; in a few lizards, five. But the number was
much more inconstant among the older reptiles; some of the
plesiosaurs had as many as seventy-six cervical vertebrae; some of
the older lizards even had as many as eighteen.

 
32 WATER REPTILES OF THE PAST AND PRESENT

Ordinarily the cervical vertebrae differ from those behind them
only in the small size or fusion of their ribs; sometimes, however,
as in the Protorosauria and Pterosauria, the vertebrae may be much
elongated. The dorsal vertebrae of reptiles vary in number from
ten in turtles and some dinosaurs to forty-three in Pleurosaurus;
and under the name dorsal we
include the so-called lumbar, as
there is seldom any real distinction
between the two series, save the
smaller size or the co-ossification
of the ribs of the Jatter.

The sacrum in reptiles primi-
tively consisted of a single verte-
bra, which bore a large rib on each
side for the support of the pelvis.
Very early, however, a second or
even a third vertebra was added

to it from behind. The number

Hite 25 Ophescoden, & DHMIANE eda the: Tule among reptiles

theromorph reptile: proatlas, atlas, : 2

and axis, with ribs. both ancient and modern; among

crawling reptiles the number never

exceeds three, but among ambulatory and flying reptiles the num-
ber may be as great as in any mammal.

The number of caudal vertebrae in reptiles is exceedingly
variable, from a dozen or fifteen up to a hundred and fifty or more.
In snakes but two regions are
distinguishable, the caudal
and precaudal, and the num-
ber altogether may reach
nearly five hundred. With
the exception of the’ first ua
few basal caudal vertebrae Fie. ¥6 —Saceam-ot Chelone
(pygals) and the minute ones
at the extreme tip, all caudal vertebrae of reptiles bear a slender,
usually Y-shaped bone below in the interval between the centra, for
the protection of the vessels and nerves. Because of their shape
they have been called chevrons, and are really outgrowths from the
intercentra.

 

 
THE SKELETON OF REPTILES 33

The ribs of reptiles are of more importance in classification than
one would suppose. The primitive rib was a slender, curved bone,
with the vertebra] end dilated to articulate continuously with the
intercentral space—that between the centra and the anterior
part of the arch. And this is the condition still remaining in the
tuatera. Very soon, however, the lower end of the articular
surface (capitulum) became separated from the upper (tubercle)
by a notch, -and the ribs became distinctly double-headed. And
this mode of articulation is the rule among mammals. Among
later reptiles, however, there were many modifications. In nearly
all the head migrated a little backward on the centrum. By the
loss of the tubercle in lizards, the head became truly single-headed,
and attached solely to the body;
and this condition is character-
istic of the order Squamata. In
another large group the head of
the rib gradually migrated up on
the arch and on the transverse
process (diapophysis), so that
both head and tubercle are
attached to the diapophysis; .
and this condition is equally Fic. 17.—Ostodolepis, a primitive
characteristic of the orders of cage Zepliley  Nentebriis Hota) au

ront and side, with primitive double-
reptiles known collectively as headed rib and intercentrum.
the Archosauria—the crocodiles,
pterodactyls, dinosaurs, and phytosaurs. In the Sauropterygia, the
ribs are single-headed and attached to the end of the diapophy-
sis. Finally in most ichthyosaurs the capitulum and _ tubercle
both articulate with the body of the vertebra.

Ribs primitively were probably attached to all the vertebrae
to the end of the tail. In the earliest reptiles that we know they
are present on all vertebrae as far back as the tenth or twelfth
caudal only, those of the caudal for the most part co-ossified
with the centra. The ribs of the neck vertebrae more quickly
disappeared, or became fused with the vertebrae, and only in the
crocodiles among living reptiles are there ribs on the atlas. The
sacral ribs, on the other hand, became much larger and stouter and

 
34 WATER REPTILES OF THE PAST AND PRESENT

developed an articulation at their outer ends for the support of the
ilium (Fig. 16).

The so-called ventral ribs are slender ossifications in the con-
nective tissue under the skin, on the under side of the body, and
are characteristic of most reptiles. The anterior ones doubt-
less fused together more or less to form the sternum or breast
bone, which was otherwise absent in the early reptiles.

PECTORAL OR SHOULDER GIRDLE

Those bones which form the framework for the support of the
anterior extremity in vertebrate animals are known collectively
as the pectoral girdle. In our own skeleton there are but two on
each side, or four in all, the scapula or shoulder-blade, and the
clavicle or collar-bone. A ‘third bone, however, is represented
in all mammals by a mere vestige which early unites with the
scapula and is called the coracoid process. In the lowest forms
of mammals, the Monotremata, of which the Ornithorhynchus and
Echidna are the only éxamples, not only is this coracoid bone
largely developed, articulating with the sternum or breast bone,
but there is an additional coracoid bone in front of this; and
there is also an interclavicle. Indeed, the pectoral girdle in
these mammals is more primitive or generalized in structure
than it is in any living reptiles, composed of scapula, coracoid,
metacoracoid, and clavicle on each side and an interclavicle
in the middle: No living reptiles have the metacoracoid, and,
as is the case with many mammals, some reptiles have no
clavicles.

Primitively, that is, in all the old reptiles, the girdle is composed
of scapula, coracoid, metacoracoid, clavicles, and interclavicle,
while in some of the very oldest there is yet another bone, more or
less of a vestige, derived from the ancestral amphibians and called
the cleithrum or supraclavicle. The scapula is more or less
elongated in crawling and climbing reptiles; more slender and
bird-like in those which walked erect after the manner of birds and
mammals; shorter and more fan-shaped in the swimming reptiles,
as we shall see. In some pterodactyls, unlike all other known
animals, the scapula articulated at its upper end with the backbone,
giving a much firmer support for the anterior extremities. Only
THE SKELETON OF REPTILES

in those reptiles allied
to the ancestors of the
mammals has the
scapula ever had a
spine or projection on
its dorsal side.

Of the two coracoid
bones in the original
pectoral girdle the
posterior one began
to disappear early and
is entirely lost in all
reptiles that lived later
than Triassic times,
though it still persists
in the lowest mam-
mals, as we have seen.
In most later reptiles
the remaining coracoid
has become less firmly
attached to the scapula
than it was in the older
reptiles. It usually
has a small foramen
piercing it near the
middle of the upper
border or end, the
supracoracoid fora-
men. The clavicle,
while more constant
among reptiles than
among mammals, has
been lost in some, the
Crocodilia, for in-
stance, as also the
dinosaurs and ptero-
dactyls. The inter-
clavicle is more

Fic. 18.—Cacops, a Permian stegocephalian, ancestrally allied to the primitive reptiles, with rhachitomous vertebrae and large cleithrum

above the scapula.

 

w°:
wn
36 WATER REPTILES OF THE PAST AND PRESENT

constant in reptiles, a more or less T-shaped bone underlying the
coracoids where they join, or the breast bone; but there were some
reptiles that lost it, the dinosaurs and pterodacty]s, for instance.
In the turtles both the clavicles and the interclavicle form a part
of the under shell or plastron.

 

Fic. 19.—Scapula (sc), coracoid (cor), and metacoracoid (mcor) of Dimetrodon

The cleithrum is known in only a few of the old reptiles; it
is a more or less slender bone which lies along the upper front
margin of the scapula, articulating at its lower end with the upper
end of the clavicle on each side.
THE SKELETON OF REPTILES 37

The breast bone or sternum, while not properly a part of the
pectoral girdle, may be mentioned here. In reptiles it is rarely
well developed or even ossified, the flying reptiles known as the
pterodactyls being the most notable exceptions. It was a com-
paratively late development in this class, the earliest ones not
possessing it even in a cartilaginous condition. It was doubtless
evolved from the more or less numerous and slender ossifications on
the under side of the body called ventral or abdominal ribs, after

 

Fic. 20.—Clavicles and interclavicle of Ophiacodon, « theromorph reptile from
the Permocarboniferous of Mew Mexico.

the coracoids had become reduced and more slender. Whenever
it is present the coracoid articulates with it on each side in front.
In most lizards it remains as a cartilage throughout life.

ANTERIOR EXTREMITY

The upper arm bone, or humerus, like most other bones of the
extremities, has been greatly modified by the habits of the different
reptiles. In running and climbing reptiles it is always slender,
while in burrowing reptiles it is short and stout and much expanded
at the extremities, like the humerus of the mole among mammals.
And we shall also see how greatly modified it was among the
38 WATER REPTILES OF THE PAST AND PRESENT

swimming reptiles. The humerus of flying reptiles has an enor-
mous process on the side, corresponding to the attachment of the
deltoid muscle. The head of the humerus, for articulation with the
glenoid cavity of the scapula, is rounded in all reptiles, except the
pterodactyls, and the articulation is always at the extremity. At
the lower extrem-
ity the protuber-
ance at the outer or
radial side is called
the ectocondyle;
that on the inner
or ulnar side,- the
entocondyle. Be-
tween the two at
the end are the
articular surfaces for the radius and ulna,
the capitellum and trochlea. A little above
each of these condyles there is usually, on
one side or the other or on both, a foramen
or hole for the passage of arteries or nerves.
That on the inner side, which is character-
istic of all early reptiles and of many
mammals, is called the entepicondylar
foramen; that on the outer side, the ectepi-
condylar foramen; the latter is present in
the lizards, and both are found in the
tuatera and some of the early reptiles.

The radius and ulna are always distinct

Fic. 21—Anterior ex. Pones in reptiles, and always freely mov-
tremity of Ophiacodon. able on each other; they are usually shorter
than the humerus, but in some springing

and climbing reptiles they are quite as long.

The carpus or wrist of reptiles consists primitively of eleven
distinct, irregularly shaped bones, which articulate more or less
closely with each other in three rows. Those of the first row, all
true carpals, are known usually as the radiale, intermedium, ulnare,
and pisiform, corresponding quite with the bones of the human wrist

   
 
THE SKELETON OF REPTILES 39

known as the scaphoid, Junar, cuneiform, and pisiform. The second
row has but two bones, on the radial side, known as the centralia;
while the third row has a bone to correspond to each of the meta-
carpals, five in number, and collectively known as the carpalia.
Some or indeed all of these bones may be either absent or unossified,
that is, remaining through life as nodules of cartilage. Seldom,
however, are there less than nine bones in the carpus of reptiles.

The metacarpals, like the digits, primitively were five in number,
and seldom are there less, though the fifth is sometimes lost, and
rarely also the first. They are more or less elongate bones, increas-
ing in length from the first to the fourth, with the fifth usually
shorter. The first and the fifth are usually more nee movable
on the wrist than are the other three.

The number of joints or phalanges in the fingers of’all primitive
reptiles is that of the modern lizards and the tuatera, that is, two
on the first finger or thumb, three on the second, four on the third,
five on the fourth, and three on the fifth. The crocodiles have one
less phalange on the fourth digit; the turtles have usually two
less on the fourth and one less on the third, that is, with precisely
the same arrangement that is found in our own fingers and that of
mammals in general, two on the thumb and three on each of the
other fingers. As exceptions the river turtles have four bones in
the fourth digit. And this mammal-like and turtle-like arrange-
ment of the phalanges was that of those early reptiles, the Therio-
dontia, from which the mammals arose. The last or ungual
phalange of reptiles is usually claw-like, that is, sharp, curved,
and pointed, but sometimes it is more nail- or hoof-like.

PELVIC OR HIP GIRDLE

The pelvic girdle or pelvis in reptiles and higher animals con-
sists of three bones on each side, often closely fused in adult reptiles
and together known as the innominate bone. The upper or dorsal
one of these three bones—that to which the sacrum is attached—
is the ilium; the one on the lower or ventral side in front is the
pubis; and that on the ventral side behind is the ischium: On
the outer side, where these three bones meet, is a cup-like depres-
sion, sometimes a hole, called the acetabulum, for the articulation.
40 WATER REPTILES OF THE PAST AND PRESENT

of the head of the thigh bone, homologous with the glenoid articu-
lation of the pectoral girdle, which, as we have seen, was originally
formed by three bones, the scapula, coracoid, and metacoracoid,
the two latter bones, like the pubis and ischium, meeting in the
middle line below. In all the primitive and early reptiles the pubis -
and ischium form a continuous plate of bone without holes in it,
except a small one just below the acetabulum in the pubis, called

 

the obturator foramen, and correspond-
ing to the supracoracoid foramen of
the coracoid. One may almost always
recognize these two bones by the presence
of the foramen. This “‘plate-like’’ con-
dition of the pelvis has been lost in all
Jate and modern reptiles by the appear-
ance of a larger or smaller vacuity Heay Ac Heoen elder eon
between the pubis and ischium, either hove; pu, pubis; ii, ilium; is,
paired, when it corresponds quite with  ischium.

the so-called obturator opening of mam-

mals, or singly in the middle. This old-fashioned character, like
the old-fashioned type of pectoral] girdle, disappeared entirely about
the close of the Mesozoic period, the Choristodera, described in
the following pages, being the last of the kind.

The ilium in reptiles usually has a more or less prolonged process
or projection turned backward by the side of the anterior caudal
vertebrae, but in those animals which walked erect on the hind
legs, the dinosaurs and pterodactyls, as also some of the more

 

Fic. 22.—Pelvis of Ophiaco-
THE SKELETON OF REPTILES 4I

erect-walking reptiles ancestral to the mammals, this process was
directed forward, as in birds and mammals. The crocodilia,
unlike all other known reptiles, have the pubes excluded from the
acetabulum, and they do not meet in a median symphysis. This
character alone will distinguish any crocodilian from all other
reptiles. But there is some doubt as to the homology of the bones
usually called pubes in the crocodiles. Some of the bipedal
dinosaurs have the pubis forked, the anterior part directed down-
ward and forward, and not meeting its mate in a symphysis, the
posterior process long and slender, lying below the long ischium,
as in birds. Indeed, when this peculiarity of the dinosaurian
pubis was first discovered, it was thought to be an evidence of the
immediate relationship of birds; its structuré is now interpreted
differently.
POSTERIOR EXTREMITY

The thigh bone or femur in reptiles, like the humerus, is variable
in size and shape. Only in those reptiles that walked erect is the
articulation of the head set off from the shaft of the bone by a
distinct neck. In others the articulation is at the extreme top of
the bone, since the thigh bones are habitually turned more or less
directly outward from the acetabulum and the long axis of the body.
The more or Jess pronounced rugosities at the upper end of the
femur, for the attachment of muscles, called trochanters, are not
easily distinguishable into the greater and lesser, as in mammals.
Sometimes, as in the erect-walking dinosaurs, there is a more or
less pronounced process on the shaft lower down, called the fourth
trochanter, for the attachment of caudal muscles. On the back
part of the shaft there is a ridge or line for the attachment of
muscles, corresponding to the linea aspera of the mammalian femur.
The projections at the lower end on the sides are called condyles.

The two bones of the leg, or shin, are usually shorter than the
thigh bones, though in running and leaping animals they may be
quite as long or even longer. That on the inner or big-toe side is
called the tibia, and articulates with the distal end of the femur,
but chiefly with its inner condyle. It has a more or less well-
developed crest in front above for the attachment of the extensor
muscles directly, since there never is a patella in reptiles, and only
42 WATER REPTILES OF THE PAST AND PRESENT

rarely sesamoid bones of any kind. The fibula, at the little-toe side
of the leg, is usually more slender than the tibia, though it may be
larger in swimming reptiles and even in some running forms. It
disappeared in some of the later pterodactyls. Its upper articula-
tion has a more gliding and somewhat rotary motion on the
outer condyle of the femur,
turning the foot outward
in extension of the leg.
The tarsus of reptiles
differs from that of mam-
mals, in that the chief
movements of extension
and flexion of the foot
upon the leg occur within
the tarsus rather than
between. the tarsus and
leg bones. Primitively the
tarsus of reptiles consisted
of nine bones, two in the
first row, two in the second, and five in
the third, but in all modern reptiles the
bones of the middle row and the fifth one
Fic. 23—Right hind in the third row have disappeared; in some
foot of Ophiacodon: «, Jizards and turtles the two of the first row
ier ea are fused. The two bones of the proximal
4, 5, tarsalia. row correspond quite to the astragalus and
calcaneum, the astragalus articulating with

both tibia and fibula proximally, the calcaneum with the latter
only. The cldest known tarsus of any vertebrated animal, one
from the Coal Measures of Ohio, has this structure, while in all
the early amphibians there were three bones, the tibiale, inter-
medium, and fibulare. Some of the later swimming reptiles, like
the ichthyosaurs and plesiosaurs, have apparently this amphibian
structure, with three bones that are usually called tibiale, inter-
medium, and fibulare, but it is very doubtful indeed whether
they are homologically the same. In the middle row two centralia
are known in one or two very ancient reptiles, but for the most

   
THE SKELETON OF REPTILES 43

part there is only a single centrale, and even that is usually
lost in later reptiles. The third row, like the third row of the
carpus, had a distinct bone for each digit originally, but the fifth
one was very soon lost and has never reappeared. The structure
of the digits and number of bones are quite like those of the hands,
except that the fifth toe has four bones instead of three, that is,
the phalangeal formula was 2, 3, 4, 5, 4. Asa rule in terrestrial.
reptiles, as in terrestrial] mammals, the hind foot is more specialized
than the front ones.

Most reptiles have an external covering or exoskeleton of horny
plates or scales or bony scutes. Horny scales are of course not
preservable as petrifactions, though in many instances their
actual carbonized remains or their impressions have been detected.
Such information comes only rarely, though doubtless in the
course of time we shall obtain it for most extinct reptiles. In the
mosasaurs, for instance, very perfect impressions showing the
detailed structure of the scales have been frequently found. Similar
impressions were long since observed by Lortet in Pleurosaurus,
and in not a few dinosaurs impressions of most wonderful perfec-
tion have been found. It is only in the water reptiles, probably,
that all external coverings tended to disappear.

Bony dermal plates or scutes are less common among reptiles,
though by no means rare. The turtles, as is well known, are
almost completely inclosed in such an exoskeleton, bones which
have coalesced more or less to form a box or carapace within
which the head and limbs may be withdrawn for protection.
In the modern crocodilians also the body is more or less protected
by small bone plates forming rows on the back and sometimes
on the under side. The ancient phytosaurs had similar plates.
Not a few of the dinosaurs were more or less covered with bony
scutes and sometimes with large bony plates or spines. Some
modern lizards have bony plates over the body instead of horny
scales.
CHAPTER IV
THE AGE OF REPTILES

* Geologists divide the history of the earth, since life first appeared
upon it, into four general eras, the Proterozoic, Paleozoic, Mesozoic,
and Cenozoic, that is, into eras of first life, ancient life, middle
life, and recent life. These divisions were made long ago by geolo-
gists when it was believed that extraordinary changes, great cata-
clysmic revolutions, marked their limits.

With a fuller knowledge of the life of the past we know that
evolution has been continuous and uninterrupted; possibly acceler-
ated or retarded at times, but without break. Were the earth’s
history to be written anew, with our present knowledge, and with an
unbiased mind, it is very doubtful whether many of the time
divisions would have the same limits that they have now—-whether
the Paleozoic would terminate with the Carboniferous, or the
Permian, or the Trias, or whether indeed we should think it neces-
sary to make any primary divisions whatsoever. In other words,
our greater knowledge of living and extinct organisms, and of the
rocks which contain fossils, has made the problems of classification
much more complex than they seemed to be formerly. It is much
easier to classify organisms or rocks, or anything else, when we
know only a few isolated kinds—much easier to draw divisional
lines. Geological history is like a volume in which pages, leaves,
and even whole chapters either are missing or are printed in lan-
guages which we understand only imperfectly. Where the lost or
unknown parts belong, the largest divisions may be made, and
possibly such may have been epochs of unusual activity, of dias-
trophic changes which greatly accelerated organic evolution. No
one can say just where the dividing line should be drawn between
the rocks of Paleozoic and Mesozoic age, or between the Mesozoic
and Cenozoic, for there is none; the most that we can hope for is to
make the divisions everywhere in the world conform to those first
made for local reasons.

44
45

THE AGE OF REPTILES

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46 WATER REPTILES OF THE PAST AND PRESENT

The periods of the Paleozoic era are the Cambrian, Ordovician,
Silurian, Devonian, Carboniferous, and Permian, in the order as
given; those of the ‘Mesozoic era are the Triassic, Jurassic, and
Cretaceous; those of the Cenozoic era, the Eocene, Oligocene,
Miocene, Pliocene, Pleistocene, and Recent. As a relic of an old
classification we still often divide the Cenozoic into two quite
arbitrary divisions, the Tertiary and the Quaternary, the latter
including the Pleistocene and Recent only. The same may be
said regarding the limits of each of these periods as of the eras;
the sole problem is to make each period contemporaneous through-
out the world, an exceedingly difficult problem, because no faunas
or floras have’ever been the same over the whole earth. Indeed,
with the exception of some of the lowliest and most generalized
forms, or man himself, no species are the same throughout the
earth today. Inasmuch as we must depend upon the fossils in the
rocks for the determination of the ages, where none is quite the
same in strata of remote localities the identification becomes very
difficult or even impossible. Nor are the periods, as accepted,
of equal or even approximately equal duration; the Cretaceous
period, for instance, was longer than all the remainder of the
Mesozoic, longer perhaps than all the time which has elapsed since
its close.

The earliest animals with a backbone, or rather the earliest that
we call vertebrates—for some vertebrates have no vertebrae—
began their existence, so far as we know, in late Ordovician times,
as attested by fish bones in Ordovician rocks of Colorado and Utah.
The first evidences of the existence of air-breathing vertebrates
in geological history are footprints preserved in the uppermost
Devonian rocks of Pennsylvania. We call them amphibian because
they resemble footprints associated with amphibian skeletons in
later formations, and because the foot itself is stil] the most impor-
tant difference we know between fishes and the higher animals.

In the rocks of the next great time division, the Mississippian, as
we call it in America, corresponding more or Jess closely with the
Lower or Subcarboniferous of other parts of the world, numerous
footprints of amphibians have been discovered, but no fossil
remains except a few from near its close in Scotland. From the
47

THE AGE OF REPTILES

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48 WATER REPTILES OF THE PAST AND PRESENT

Upper Carboniferous, or Pennsylvanian, however, not only numer-
ous footprints but the actual] skeletons, or impressions of skeletons,
have long been known in Europe and America. Until recently
all these footprints and skeletons were supposed to be exclusively
amphibian. We are now almost sure that some of them belonged
to reptiles of lowly type, the earliest coming from near the middle
of the Pennsylvanian of Linton, Ohio. The amphibians of this
period were, for the most part, salamander-like creatures of from a
few inches to two or three feet in length. They al] belong to the
group collectively known as the Stegocephalia, except that very
near the close of the period there appeared small, slender, small-

 

 

 

 

 

Fic. 25.—Restoration of Seymouria, the most primitive of known cotylosaur
reptiles. From the Permian of Texas, about two feet long.

legged aquatic forms which seem to be the ancient representatives of
the real salamanders of modern times. Some of the Stegocephalians
had become greatly specialized as legless, snake-like, or eel-like
creatures.

By the beginning of Permian times tremendous changes had
taken place in the land. life. The small amphibians of the Car-
boniferous types dwindled away, soon to disappear, and their
places were taken by others of peculiar types, for the most part
larger; and by many and diverse kinds of reptiles—-water reptiles,
marsh reptiles, land reptiles, and even climbing tree reptiles.
From the uppermost Carboniferous and Lower Permian ‘rocks of
THE AGE OF REPTILES 49

the United States more than fifty genera and twice that many
species of amphibians and reptiles have been made known in
recent years, and doubtless as many more will be discovered in the
future. From other parts of the world the history of reptiles of
the Lower Permian is yet scanty, two or three forms from South
America, as many more from Africa, and a half-dozen or so from
Europe are all; and of these very few are known at all well.

We classify all the known forms of reptiles from the Lower
Permian under three or four orders,
the Cotylosauria, Theromorpha or
Pelycosauria, Proganosauria, and
possibly the Protorosauria, but the
classification is yet provisional,
representing merely the present
stage of our knowedge. The Pro-
ganosauria and Protorosauria,
including distinctively aquatic
reptiles, will be more fully
described in the following pages.
To give even a brief description of
the more terrestrial reptiles of this,
the earliest known reptilian fauna,
would be beyond our purpose; the
accompanying life restorations by
the author of some of the more
typical and better known forms,
based upon nearly perfect skele-
tons, will suffice.

From the reptiles and amphib-
ians of the Lower Permian of Texas and New Mexico to the
ichthyosaurs of the Middle Triassic of California there is a
complete gap in the records of the land life of North America.
We do not know what became of all the remarkable animals
of the Permian. There are few traces of their descendants else-
where known, unless it be in South Africa. From the Middle
and Upper Permian of South Africa and Russia, a marvelous rep-
tilian fauna has been made known in recent years. More than a

 

 

 

 

 

Fic. 26.—Caplorhinus, a cotylosaur
reptile from Texas, about one-fourth
natural size.
50 WATER REPTILES OF THE PAST AND PRESENT

hundred species of six or seven groups, and at least two orders have
been described. Of these the Cotylosauria are the continuation
of the American order, but include more specialized forms, the
Pareiasauria and the Procolophonia, all of them, like the more
primitive American forms, characterized by the imperforate
temporal region. The Therapsida, likewise, seem to be the con-
tinuation of the American Theromorpha, so closely allied to them
that it is difficult to draw a distinguishing line between them.
On the other hand, these African reptiles merge through the
Theriodontia into the mammals in the Triassic. They are all

 

 

 

 

 

Fic. 27.—Restoration of Labidosaurus, a cotylosaur reptile from Texas, about

three feet long.
|

terrestrial, crawling reptiles, except a few which are described
on a later page under the Anomodontia.

The records of the lower part of the Triassic period are scanty
everywhere in the world, save perhaps in Africa. Before the close
of the period, however, probably every important group of cold-
blooded air-breathing animals had made its appearance in geological
history, if we except the snakes; even the mammals had appeared,
and possibly the birds. The Cotylosauria, Theromorpha, and
Therapsida disappeared, the latter giving birth to the mammals;
the nothosaurs and plesiosaurs, the ichthyosaurs, dinosaurs, croco-
diles, phytosaurs, rhynchocephalians, lizards, and turtles have all
left records of their existence in Upper Triassic rocks; and the
pterodactyls had also, in all probability, begun their career,
though none is surely known till the Jurassic.
THE AGE OF REPTILES 51

During Jurassic times all these orders of reptiles waxed pros-
perous and powerful, and branched out in many ways and in count-
less numbers; many new kinds of each appeared—the marine
crocodiles, the quadrupedal dinosaurs, etc.—but no order or sub-
order, so far as we know, disappeared before its close. And this
prosperity continued on into the Lower Cretaceous and for many
even into the Upper Cretaceous. The largest dinosaurs disappeared
in the Lower Cretaceous, so far as our knowedge goes, but the

 

 

 

 

 

Fic. 28.—Restoration of Dimetrodon, a pelycosaur reptile from the Permian of
Texas; about eight feet long.

old-fashioned crocodiles continued on into the Upper, to give place
to the new-fashioned kinds. The ichthyosaurs lingered on for a
while on the western continent, but the mosasaurs appeared, and
the plesiosaurs reached their highest evolution and continued
to the end. The flying reptiles attained the zenith of their evolu-
tion, but disappeared before the close. The marine turtles attained
the maximum of specialization and size. The upright-walking
dinosaurs continued on unabated to the close of the period; and a
new kind of dinosaurs appeared near the end.
52 WATER REPTILES OF THE PAST AND PRESENT

With the opening of the next great era—the Cenozoic or Tertiary
—the reptiles dwindled away to their present insignificant position,
while the birds and mammals appeared in great numbers and
varied forms. The Age of Reptiles was closed and the Age of
Mammals had begun.

The history of the reptiles during the Cenozoic is an uneventful
one; they ceased their dominion upon land, in the water, and in the
air. Their remains are scanty, for the most part, in the rocks of
the Tertiary, and such as are known differ only in details from those
now living. The land tortoises only, like the mammals of Oligocene
and Miocene times, seized the opportunities of open prairies and
prospered. A few of the late Mesozoic forms continued a short
while into the Eocene. No new groups, perhaps few new families,
came into existence during the greater part of this time; it was’
the age only of land tortoises and the poisonous snakes among
reptiles.

EXTINCT REPTILES OF NORTH AMERICA

The oldest known fossil reptile of North America, or indeed
of the world, is represented by a single specimen, lacking the skull,
from black shales of Middle Pennsylvanian age overlying a coal
seam at Linton, Ohio. The specimen was originally described as
an amphibian, but was later recognized by Professor Cope as a true
reptile. It was more fully described by the writer under the name
Eosauravus Copei, who agreed with Cope as to its reptilian nature.
Until the skull is discovered, however, the precise relationships of
the animal must remain doubtful.

The next later rocks that have yielded reptilian remains are
those of Illinois and Texas formerly supposed to be of Permian age.
Later evidence, furnished by invertebrates, however,. seems to
prove that the lowermost of the strata are of uppermost Carbonifer-
ous age. The Illinois deposits, so far as known, are of very limited
extent, censisting practically of a single bone-bed in black shale in
the immediate valley of the Kaskaskia River near Danville. The
known fossils from this bone-bed—all isolated bones—are preserved
in the museum of the University of Chicago, and include the types
of several genera later recognized in the Texas deposits.
THE AGE OF REPTILES 53

The deposits of Texas, extending northward through Oklahoma
to the south line of Kansas, are of considerable extent, for the most
part lying along the Wichita River and its tributaries, north of
Seymour, Texas. They are composed chiefly of red clays and
sandstones of fresh-water or delta origin, perhaps eight hundred
feet in total thickness. Beds of like character and yielding similar
fossils are also known from northern New Mexico on the tributaries
of the Chama River. Their chief characters, as well as restorations
of some of the more noteworthy forms, have already been given.

No vertebrate fossils are known in America from the Upper
Permian and Lower Triassic. Marine limestones of Middle and

 

 

 

weep ns

Fic. 29.—Restoration of Varanops, a theromorph reptile from the Permian of
Texas; about four feet long.

Upper Triassic age of Nevada and northern California have yielded
numerous remains of primitive ichthyosaurs, the only known re-
mains of the thalattosaurs, and a few others of doubtful affinities,
all of which have been described by Dr. Merriam. The Upper
Triassic exposures, of considerable extent, occur between the Pitt
River and Squaw Creek in Shasta County, California. Reptilian
remains from the Middle Triassic are so far known only from the
limestones of West Humboldt and New Pass regions of western and
central Nevada.

Land reptiles of Middle and Upper Triassic age are known from
many widely separated localities in the United States, but chiefly
from the extensive “red beds” of the Rocky Mountain region.
54 WATER REPTILES OF THE PAST AND PRESENT

The fossils from these beds occur for the most part at least in the
horizon called the Shinarump. Its age is usually considered to be
Upper Triassic, but the character of the fossils seems to indicate
possibly the Middle Triassic. Aside from the stereospondylian
amphibians, the last of the Stegocephalia, the vertebrates from this
horizon and these regions are chiefly Phytosauria. A few anomo-
donts, or what seem to be anomodonts—the only record of their
occurrence outside of Africa—are known from Wyoming and Utah.
And a single specimen from the Wind River red beds, described
by the writer as Dolichobrachium, may represent reptiles allied to
the dinosaurs. Phytosaur fossils of this horizon have been dis-
covered in Utah, the Wind River Mountains, and near Laramie
City in Wyoming; in southwestern Colorado; in western Texas;
and in various places in New Mexico and Arizona. Doubtless
when these fossiliferous beds are more thoroughly explored many
new and interesting reptiles will be discovered.

Phytosaur remains, probably of about the same age as the Rocky
Mountain ones, have long been known from the Triassic of North
Carolina. From somewhat more recent Triassic deposits in Con-
necticut and Massachusetts, several skeletons of small carnivorous
dinosaurs, and various parasuchian remains have been described
by Marsh, Lull, and Talbot. And these beds have long been
famous in Massachusetts for their footprints, for the most part
originally referred to birds, but now pretty well known to have
been made by dinosaurs and amphibians.

No vertebrate fossils of Lower or even Middle Jurassic age are
known from North America. From the Baptanodon beds of Wyo-
ming, limestones of about two hundred feet in thickness, four
genera of plesiosaurs, the very peculiar ichthyosaur from which
the beds take their name, and a few bones of an ancient crocodile
are known.

Immediately overlying the Baptanodon beds, the Morrison beds,
of from two hundred to four hundred feet in thickness, probably
of Uppermost Jurassic and Lowermost Cretaceous age, have yielded
an exceedingly rich vertebrate fauna, consisting chiefly of dinosaurs.
Discovered first in the vicinity of Morrison, Colorado, in 1877,
hundreds of tons of bones have been collected from these beds for
THE AGE OF REPTILES 55

various museums. The dinosaurs include many genera of all three
suborders, varying in size from that of a cat to some of the largest
known land animals. Of other reptiles a very few jaws of a true
rhynchocephalian, a fragment of a wing bone of a pterodactyl,
numerous turtles, and crocodiles, only, are known. The beds are
predominantly black-clay shales, intercalated with sandstones, and
all are of fresh-water origin.

From beds definitely known as Lower Cretaceous (Trinity)
in Oklahoma, a few bones of a sauropod dinosaur are known, and

 

 

 

Fic. 30.—Restoration of Casea, a theromorph reptile from the Permian of Texas,
about four feet long.

from nearly corresponding rocks in southern Kansas, plesiosaurs,
crocodiles, turtles, and carnivorous dinosaurs are known from
sparse remains. Doubtless the Potomac beds of Virginia, which
have yielded bones of various dinosaurs, are also of Lower
Cretaceous age.

With the exception of a single vertebra of doubtful affinities
and the cast of a turtle-shell no vertebrate fossils have ever
been discovered in the extensive sandstones of Dakota age, the
lowermost of the Upper Cretaceous. From the next horizon above
the Dakota, the Benton Cretaceous, chiefly marine limestones, at
56 WATER REPTILES OF THE PAST AND PRESENT

least three genera of plesiosaurs are known from Kansas, Texas,
and Arkansas, with two or three more from the limestone shales
of Wyoming. A few specimens of armored dinosaurs, two genera
of ancient crocodiles, nearly the last of their kind, some marine
turtles, and a few vertebrae of ichthyosaurs, the last of the order
known anywhere in the world, are also known from the Benton
Cretaceous of Wyoming.

Continuous with the Benton limestones above in Kansas are
the famous beds of Niobrara chalk; perhaps no fossil deposits in
the world are more famous. Exposures covering hundreds of
square miles in western Kansas, almost pure chalk, have furnished
fossil-hunters during the past forty years literally thousands of
specimens of mosasaurs, hundreds of pterodactyls, and scores of
plesiosaurs and marine turtles, in addition to the famous birds with
teeth and countless fishes of diverse kinds. Two or three specimens
of spoon-billed dinosaurs have been found in these deposits, but no
other reptiles of any kinds. Beds of like age in Colorado and New
Mexico have furnished a few specimens of mosasaurs.

From the marine beds of Fort Pierre age, next above the Nio-
brara in the west, have come some excellent specimens of two genera
of mosasaurs, three or four forms of plesiosaurs, a few pterodactyls,
the largest of all marine turtles, and still fewer specimens of dino-
saurs, in Kansas, South Dakota, Wyoming, and Montana. From
deposits of approximately like age in Mississippi, Alabama, and
New Jersey, many incomplete specimens were found years ago of
mosasaurs, plesiosaurs, and turtles, the last of the amphicoelian
crocodiles, the first of the procoelian crocodiles, and the famous
specimen of Hadrosaurus which served for the Hawkins restoration,
the first attempt of its kind.

From the uppermost Cretaceous beds of America, the Lance,
Judith River, or Belly River beds as they are variously called, have
come the remains of a marvelous reptilian fauna. These beds may
be grouped together though not all contemporaneous, and there is
dispute about their age, some excellent paleontologists insisting
that the uppermost are really of Eocene age. From Colorado east
of Denver, from eastern Wyoming, from Montana, and especially
from the vicinity of Edmonton in Canada, as also occasionally in
THE AGE OF REPTILES 57

western Texas and New Mexico, have come many marvelous speci-
mens of dinosaurs, huge bipedal carnivorous dinosaurs, great spoon-
billed aquatic dinosaurs, armored stegosaurian dinosaurs, and many
kinds of the great horned dinosaurs, the Ceratopsia, so far known
only from these beds. Here at the very close of the Age of Reptiles,
at the close of the Age of Dinosaurs, are found the ultimate speciali-
zations of all the chief groups of dinosaurs except the long-necked
quadrupedal dinosaurs which gave up the ghost in Lower Cretaceous
times. Many were provided with horns and spines, some indeed
seemed to have bristled with spines throughout, a sure sign that
they were approaching the end of their career. The modern type
of crocodiles had usurped the ancient forms of the early Cretaceous,
and reached the largest size of their race perhaps, though but few
specimens are known. Here also in these beds we find the first
representatives of lizards and snakes in America, though snakes
have been described from earlier strata, perhaps, in Brazil. Those
archaic, old-fashioned ryhnchocephalians described on a later page
as the Choristodera appeared also for the first time in these beds,
and persisted for a little while in the Eocene, in Europe and America.
And with all these there has very recently been described the last of
the plesiosaurs, whose race went out with the dinosaurs at the very
close of the Mesozoic. It is needless to say that the turtles also
occur, for, as a general rule, wherever vertebrate fossils are found,
in rocks of the land or the sea, marine or fresh-water, there will
be some bones of turtles among them.

With the beginning of the Cenozoic the record of the reptiles
becomes relatively scanty in America. In the warm waters of the
old Eocene lakes and rivers of Wyoming lived countless crocodiles,
true crocodiles of modern aspect and of large size. But, as the
climate of North America grew progressively colder, the crocodiles
retreated to the south, till, in the Oligocene, the scanty remains
of the last crocodiles are found in the American Tertiary. On the
other hand, as the open lands appeared toward the close of the Eo-
cene, and in the Oligocene and Miocene, the land tortoises throve
and grew greatly in size. In the Bad Lands of South Dakota one
may see their remains in almost incredible numbers. And in
equally great numbers are these land tortoises, in shape much like
58 WATER REPTILES OF THE PAST AND PRESENT

the common box tortoise of today, but vastly larger, found in the
rocks of the late Miocene or early Pliocene age in western Kansas.
And these are the last records of the big tortoises in North America;
their descendants are perhaps yet living in the Galapagos Islands.

The history of the lizards and snakes, the only other reptiles
found in the Cenozoic rocks of America, is very brief. A few
specimens from the Lower Eocene of Wyoming; a few skinks
and amphisbaenas from the Oligocene Bad Lands of South Dakota,
and some bones of a python-like snake in the early Eocene of Wyo-
ming are about all that we know of the Squamata in the Tertiary.
Doubtless snakes and lizards were just as abandunt then as now,
though but few were preserved, for they are and always have been
distinctly terrestrial animals, that only by accident fell into places
where they could be fossilized.

The author has collected reptile bones from nearly all of the
horizons here mentioned and believes that the list is complete.
CHAPTER V
ADAPTATION OF LAND REPTILES TO LIFE IN THE WATER

In the never-ceasing struggle for existence all forms of life
upon the earth, whether consciously or unconsciously, are con-
tinuously striving for improvement; striving to flee from adverse
environments, or to adapt themselves better to those which must
be endured; to escape their enemies, or to find means whereby
they may withstand them; to find more or better food, or to pre-
vent others from despoiling them of what they have. There is
always more or less of unrest, more or less of discontent; if such
terms may be used of the lower organisms. It sometimes happens
with groups of organisms that by reason of unusual or extraordinary
traits they become so perfectly adapted to their environments, to
their surroundings, or so easily adaptable to changes in their
environments, that they remain for long ages securely protected and
little changed. But, as with man himself, improvement is usually
the result of adversity—adversity which stimulates but does not
destroy. And the word improvement, translated into biological
language, means simply specialization, that specialization which
adapts the organism better to its mode of life, which fits it the
better to excel its less ambitious or less capable competitors. No
animals or plants are perfect; if they were, there would be no
advancement, no struggle. If all physical conditions stood still,
or remained uniform, perhaps life would stand still, but conditions
never have and never will stand still, and life must change to meet
changed conditions.

Thus it is that that which makes life easier, which lessens the
dangers of destruction, which insures the continued prosperity of
the race, is seized upon and utilized by all plants and animals, so
far as possible. As said long ago by Tennyson," the first law of life

1 Are God and Nature then at strife,
That Nature lends such evil dreams ?

So careful of the type she seems
So careless of the single life—Jn Memoriam, lv:

59
60 WATER REPTILES OF THE PAST AND PRESENT

is not the preservation of self, but the prosperity of the race. What-
ever the causes may be whereby the offspring are better adapted to
conquer in the struggle for existence, whatever may be the laws
governing changes and specialization, whether heredity, Mendelism,
mutation, natural selection, or Lamarckism, we call the process
evolution.

To escape from the severe competition of the overcrowding
animals of the sea, some of those creatures we call fishes long ago
became air-breathers and took possession of the unoccupied Jand.
From among the myriads which were driven into unbreathable
water, by accident or by their enemies, or led there in the search
for more easily acquired or better food, some survived and found
that the oxygen of the air was quite as breathable as that of the
water. Steadily their progeny became better and better adapted
to the unusual life until they ceased to be fishes and became amphib-
ians, from which have arisen in like manner all the reptiles and
birds and mammals that live or have lived upon the earth.

With more and better powers, developed under better oppor-
tunities, not a few of these descendants have repeatedly sought
safety from their newly acquired enemies of the overcrowded land,
or a better supply of food in the sea; gradually, perhaps incidentally
at first, as we shall see is the case with some lizards today, but
later with increased adaptation to their new surroundings, they
become truly sea or water animals, no longer able to live upon
the land. In these changed conditions and with concomitantly
changed habits they never reverted to the primitive condition of
fishes, never became water-breathing animals again, for that would
be actual retrogression, a seeming impossibility in evolution. Nor
indeed does it seem possible that a land creature after its reversion
to water life ever can return to the land again.

A fish through long ages of evolution has become well adapted
to its environments; its shape is the best for speed or varied
evolutions in the water; its teeth and mouth-organs are best suited
for the food it requires. Now it is evident that if animals of very
different habits and form should go back to the water and seek
to compete with creatures already well adapted to their surround-
ings, they must, so far as possible, acquire like forms and. like
ADAPTATION OF LAND REPTILES TO LIFE IN WATER 61

habits. And any improvement on such forms and habits that
their higher development permits them to attain will of course be
of advantage in their competitive struggles. A fish makes most
use of its tail fin for propulsion. It follows that a land animal
seeking to compete with it under like conditions must acquire a
tail fin or some other organ which subserves its purpose as fully.
The body fins are of little use to a fish, save for equilibration, for
preserving its position, for stopping quickly, or for changing the
direction of its movements quickly—very different functions from
those of the corresponding organs, the limbs, of higher vertebrates.
There are few better examples of predaceous, fish-eating fishes than
the common gar-pike of our rivers, fishes with a slender body
covered with very smooth scales, a strong tail, a short neck, and
long jaws armed with numerous slender and sharp teeth. Such a
fish, darting into a school of smaller fishes, by quick, sudden changes
of movement, actively opening and closing its jaws, is sure to seize
some of its sought-for prey. In a direct trial of speed with its
victims it would most likely be worsted.

There have been many animals of high and low rank which in
the past and present have gone back from a terrestrial existence
to a life in the water, finding at last a congenial home away from
the shores. Or, perhaps, like the monitor lizards of today, they
have found temporary safety in the water when hard pressed by
their land enemies, and finally found, not only protection, but
an abundant supply of easily obtainable food therein. As in every
vocation of life there have been many failures in such attempts,
many partial successes only. But not a few have found abounding
and: enduring success and final prosperity—success that has led
possibly to undue adaptation to surroundings, and to the acquire-
ment of great sizé, for that has been the invariable end of water
air-breathers of long duration—specializations which finally pre-
vented them from meeting new exigencies. It seems to be a law
of evolution that no large creatures can give rise to races of
smaller creatures; and as we shall see, the largest sea animals
have been the final evolution of their respective races.

There are no better examples of such success today, nor has there
been in all the geological ages, so far as we know, more perfect
62 WATER REPTILES OF THE PAST AND PRESENT

examples of the adaptation of air-breathing animals to an aquatic
life than the great whalebone whales. In Eocene times their
ancestors were walking and running land animals; of that there
can be not the slightest doubt, since we cannot conceive, as did the
older naturalists, of their direct descent from the fishes while having
all the essential structure of mammals, i.e., lungs, circulatory sys-
tem, manner of breeding-and rearing the young, etc. Of the living
whales, or Cetacea, there are now in existence two very distinct
types, so different from each other that some have supposed them
to have been evolved from different types of land mammals. One of
these is best exemplified by the great baleen whale, having a broad,
short head and no teeth. It feeds upon crustaceans chiefly, which
are strained from the water by the great fringe or net of ‘‘ whale-
bone.” The other type is seen in the porpoise or dolphin. These
cetaceans have numerous, pointed and recurved teeth, which they
use as did many of the reptiles, hereinafter described, for the seizure
and retention of fishes and other swimming animals. So great have
been the changes in all these cetaceans, in the adaptation to an
aquatic life, that we are almost at-a loss to conjecture from what
kinds of land animals they have descended. The great zeuglodont
whales of early Tertiary times have long been thought to be a sort
of connecting link between them and their land ancestors, and it
is still probable that they were. The forms of zeuglodont whales
that have been discovered in Africa within recent years bear so
much resemblance in their skull and teeth to the contemporary
carnivores, that many paleontologists think, with good reason, that
they were descended from them, that is, from the ancestors of all
our dogs, cats, weasels, bears, etc., of modern times. And we have
much reason to believe that future discoveries will bring further
and more decisive proof of their origin before many years have
elapsed. The modern Sirenia, the dugongs and manatees, exclu-
sively aquatic mammals, which feed upon seaweeds at the bottoms
of shallow bays and harbors, or in the mouths of rivers, are now
known, practically with certainty, to be the descendants in these
same African regions of the earliest ancestors of our sheep, oxen,
and horses, known so certainly that they are often classed with
them, or at least with the elephants, which approach them in their
ancestral line even more closely.
ADAPTATION OF LAND. REPTILES TO LIFE IN WATER 63

A third type of living aquatic air-breathers is seen in the seals,
sea-lions, etc. They are much less highly specialized, however,
than the whales or sirenians, since they are still capable of con-
siderable freedom upon land, which they recurrently seek for the
breeding of their young. They still retain the primitive covering
of hair, lost almost entirely by the cetaceans and sirenians and func-
tionally replaced for the conservation of heat by a thick layer of
blubber. Instead: of losing the hind legs and developing the tail
as a propelling organ like the whales, the seals encountered pre-
cisely the reverse experience. The hind legs have been developed
into most efficient paddles or sculls, and the tail has been for the
most part lost. They are fish-eaters, it is true, but they do not
have the long jaws possessed by the porpoises and toothed whales.

In the sea-otters, beavers, and even the muskrats, we have
examples of less complete adaptation of land mammals to water
life, the most of them showing the beginnings at least of structural
adaptations similar to those of the seals. From an attentive
examination of all these animals, living as well as extinct, which
have attained partial or complete success as air-breathing water
animals, we find certain laws existing, if we may call them such,
which we may discuss a little in detail.. As we have seen in the
comparison of the whale with the seal, the methods of adaptation
have not always been the same, and some recent writers have
endeavored to classify aquatic animals under many groups, to
which they have given learned technical names, most of which will
not concern us here in dealing with the reptiles only.

Beginning with the head, we find that all those reptiles and most
of the mammals which have become aquatic fish-eaters have an
elongated skull, or rather an elongated face. The jaws are long and
slender, and the teeth are not only numerous but also sharp and
slender, much like those of the gar-pike, indeed. It is remarkable,
too, that in most such animals the external nostrils are situated,
not at the extremity of the snout, as in all terrestrial mammals
and reptiles, but far back near the eyes. In the whales this position
of the nostril enables the animals to breathe without continuous
muscular exertion while floating on the surface; that is, the nostrils
are at the top of the head. In the sirenians, on the other hand,
which live habitually at the bottom of shallow waters, coming to
64 WATER REPTILES OF THE PAST AND PRESENT

the surface to breathe only, the nostrils are situated so that they
are the first to emerge, that is, they are near the front end. The
crocodiles, with a more or less elongated face, as also the Choristo-
dera, described farther on, are exceptions, since their nostrils are
at the extremity of the snout. Both of these types, however, not-
withstanding the elongation of the face, are only partly aquatic in
habit, and in the crocodiles the breathing organs have undergone
a strange modification in accordance with habits peculiarly their
own, as will be explained later on. Whether this recession of the
nostril toward the eyes can be explained in all cases by the peculiar
breathing habits is, however, doubtful. Possibly in some cases,
such as the phytosaurs, described later, the creatures used their
long beaks to probe in the mud while breathing. Possibly the
posterior position has been in some cases rather the result of the
elongation of the face, leaving the nostrils behind in some forms,
or carrying them forward in others. Nevertheless posterior nos-
trils always indicate more or less aquatic habits.

In all the earliest reptiles, as we have seen, the neck was short,
like that of their immediate progenitors, the ancient amphibians.
The shoulders were close to the skull, with not more than two verte-
brae that could be called cervical. It happens that most of the
earliest reptiles, as we know them, were more or less amphibious in
habit, and all of them were probably good swimmers; nevertheless
in all likelihood reptiles began their career as a class with a very
short neck. The earliest known distinctly terrestrial reptiles had
a moderately long neck composed of six or seven cervical vertebrae.
It may therefore be assumed with much probability that all later
reptiles with a greater or less number of cervical vertebrae are
specialized animals, so far as the neck is concerned. Most living
reptiles have eight cervical vertebrae; a few have nine, and still
fewer have but five. Birds may have as many as twenty-four,
while all mammals, with two or three exceptions, have the primitive
number seven. Among extinct reptiles, however, there were not
a few with more numerous neck vertebrae, some having the enor-
mous number of seventy-six.

An ordinary fish has apparently no neck whatever, the trunk
being seemingly attached to the head, nearly as in the primitive
ADAPTATION OF LAND REPTILES TO LIFE IN WATER 65

amphibians and primitive reptiles. It is evident that a movable
neck of considerable length would not only be of no use to the
swiftly swimming fish, but a positive disadvantage to it. The
body is quickly and easily turned by the powerful tail fin, and a
long neck could be of no use that the tail would not better subserve.
It is therefore of interest to learn that, as a rule, aquatic animals
of all kinds having a powerfyl propelling tail have also a short neck,
acquired either by the loss of neck vertebrae, or, as in the mammals,
by the shortening and coalescence of the normal number of seven.
There are very few exceptions to this rule of a short neck and a
long tail. Those strange little reptiles of Paleozoic times, the first
that we know that returned to the water, the Proganosauria, have
not only a long, flattened tail, but also an unduly elongated neck
of from nine to twelve vertebrae.

On the other hand, certain unrelated reptiles of the past, the
dolichosaurs, nothosaurs, and plesiosaurs, with a short non-
propelling tail, developed a long neck—sometimes an excessively
long one in the plesiosaurs. The turtles, some of which have
attained a high adaptation to water life, have invariably a short
tail and a freely movable, relatively long neck, a neck which Dr.
Hay tells us has increased in length from the beginning of their
race by the simple elongation of the vertebrae, as in the giraffe,
and never by the addition of vertebrae. We may then account it a
rule that swimming animals with a long neck have a short tail, and
those with a short tail have a long flexible neck. Even in the
plesiosaurs there is some variation of the length of the tail in corre-
lation with the neck. Short-tailed animals must necessarily propel
themselves through the water by the aid of their legs, especially
the hind legs. If one watches an actively swimming alligator he
will observe that the front legs are folded or collapsed by the side
of the body, while the hind legs, much bent, are used only slightly
in propulsion. The animal swims by a marked sinuous or serpen-
tine movement, like that of a snake upon land, extending through-
out the tail and part of the body, at least. An animal propelling
itself by its limbs could not move sinuously, and use its legs actively
at the same time, and it is probable that the long neck has been
evolved compensatorily.
66 WATER REPTILES OF THE PAST AND PRESENT

With this shortening of the neck and sinuosity of movement
there is developed in every case a long trunk as well as a long tail.
The trunk becomes more slender and cylindrical, more like that of a
snake, with an actual increase of the bones composing it, reaching
the great number of forty-three vertebrae in that most sinuous of
all water reptiles with legs, Plewrosaurus of the Protorosauria.
And the tail, primitively having perhaps sixty or seventy vertebrae,
may have as many as one hundred and fifty in the more typical
aquatic forms. This elongation of trunk and tail must be of great
advantage to the swimming reptile, just as the racing scull is a
more perfect type of speedy craft than a flat-bottomed scow. Dr.
Woodward has said that the fate of all fishes, if they continue their
evolution long enough, is to become eel-like.

Not only was the tail greatly elongated in swimming reptiles,
but it was also more or less flattened. In the beginning of water
adaptation the flattening was throughout the tail, as in the living
alligators and crocodiles. As the adaptation to water life became
more perfect, the flattening became more and more restricted to the
extremity; that is, the flattening begins like that of a salamander
and in the end becomes like that of a fish, a terminal fin. And
some of the actual stages in the evolution of the fish-like fin have
been observed by Dr. Merriam in the earlier and more primitive
ichthyosaurs of California. In those animals swimming chiefly
in a horizontal direction the tail fin has become like that of fishes,
that is, vertical; but in those animals which use the tail chiefly for
ascending and descending rapidly in the water the fin is developed
in a horizontal position, examples of which are seen in the flukes of
whales and sirenians.

All animals living upon the land require firm articulations
between the different bones of the skeleton, and especially between
the vertebrae, for the support and control of the body. Among
aquatic animals there is a strong tendency toward looseness
of joints, with increasing flexibility. Fishes have the articular
processes between the arches of the vertebrae feebly or not at all
developed, and the centra or bodies of the vertebrae have thick
pads of cartilage between them. Firm union between the verte-
brae would restrict freedom of movement, and firmness is not
ADAPTATION OF LAND REPTILES TO LIFE IN WATER 67

required when the body is surrounded on all sides by water of nearly
the same specific gravity as the body itself. And it is doubtless
for the same reasons that the articulations of all strictly aquatic
reptiles have for the most part become looser and less firm, espe-
cially those between the different vertebrae.

The same looseness of articulation is also found in the ribs of
aquatic animals. In most animals, and in all those which walk
erect, like the mammals, each rib is firmly attached to the back-
bone by two distinct joints, the head and tubercle, with an interval
between them. This double attachment prevents much in-and-out
movement of the ribs and gives a firm support for the attach-
ment of the muscles of respiration, as well as for those supporting
the viscera. This firmness is unnecessary in animals living always
in the water, and the ribs therefore in all aquatic animals tend to
become single-headed and loose. The lower or capitular articula-
tion has been lost in part, or almost wholly, in many cetaceans. It
has been said that a whale cast up on land will die of suffocation,
not for the lack of air, for it is an air-breathing animal like ourselves,
but because it can no longer use its respiratory muscles attached
to the loosely articulated ribs; it suffocates because the ribs
collapse.

As would be expected, the greatest modifications of structure
in the adaptation of air-breathers to water life are found in the
limbs. No other parts of the body have such different functions in
water and on land as the limbs and fins. The limbs of a dog, ora
cat, or a man are feeble organs for swimming in comparison with the
fins of a fish, and if the land animal must compete with fishes to
prey upon them for food it must acquire like swimming powers.
As a matter of fact, the limbs of all typically aquatic air-breathing
animals have lost nearly all external resemblance to the legs of
walking and running animals, and have become more or less fin-like
in function—fin-like in shape and function, but never fin-like in
actual structure. No creature can go back and begin over again,
any more than a man can again become a child with all its possi-
bilities for improvement and development. If an animal cannot
modify the organs it already possesses so as to adapt them to new
and changed uses by the aid of evolutionary forces it must fail in

*
68 WATER REPTILES OF THE PAST AND PRESENT

the struggle. It can never acquire new material, never get new
fingers and toes, new organs or parts of organs; all its possibilities,
lie in the improved and new uses it can make of the material which
it received from its ancestors.

The beginning of aquatic adaptation of the limbs lies in the
membranous webs between the toes of frogs, salamanders, ducks,
seal, otters, etc., where the feet are used largely or entirely for pro-
pulsion through the water, in the absence of a propelling tail. And
this membrane, in the majority of cases, is the extent of aquatic
adaptation in air-breathing animals. In those animals, however,
such as most of the reptiles described in the following pages, where
the tail has developed as the propelling organ, the limbs lose to a
greater or less extent their propelling function and become merely
organs of equilibration and control. Of the two pairs of fins of fishes
it is evident that the anterior ones have the more important equili-
brational function; the hind ones have a much less important use as
guiding organs; as a matter of fact, in not a few fishes the hind or
pelvic fins have actually migrated forward to supplement the func-
tion of the pectoral fins. It is for these reasons that those animals
best adapted of all for life in the water—the whales and sirenians—
have lost the hind legs completely. In other tail-propelled air-
breathers the hind legs have become progressively smaller and —
less powerful than the front ones. In all short-tailed water animals,
however, where the legs, and especially the hind legs, have the
important function of propulsion to subserve, they still retain
the large size and firm connections with the body, examples
of which will be seen in the seals, sea-otters, marine turtles, and
plesiosaurs.

Because the legs are no longer needed for the support or propul-
sion of the body in long-tailed air-breathers, their connection with
the body becomes less and less firm, long before their entire dis-
appearance. In animals using the legs for crawling or walking
the bones of an arm and thigh are elongated, and the joints are
always well formed, permitting varied, extensive, and firm move-
ments. Just the reverse is the tendency in all those animals that
propel themselves by the aid of the tail in the water, since here what
is needed is broad, short limbs, not long and slender ones.
ADAPTATION OF LAND REPTILES TO LIFE IN WATER 69

Most reptiles have five digits on each hand or foot; the bones
of the wrist and ankle are well formed, as in mammals, and the
digits are elongate, with a very definite arrangement of the bones
composing them, as already described, never exceeding five in any
one finger or toe.

In the paddles of water reptiles, as the limbs. are usually called,
the bones of the first segment, that is, the humerus and femur, are
always greatly shortened in those having a propelling tail, and
even in some with a short tail, such as the seals, and in a lesser degree
in the sea-otters. On the other hand, in those animals which use
the legs chiefly for direct propulsion these bones are elongated, as
exemplified by the plesiosaurs and marine turtles. In all save
the seals and their kind, and the otters, whose legs are used rather
as sculls than as oars, the bones of the next segment, the radius
and ulna of the front pair, the tibia and fibula of the hind pair,
are always shortened, and one can tell the stage of aquatic adapta-
tion, as exemplified, for instance, in the plesiosaurs and ichthyosaurs
by the degree of shortening of these bones. Indeed, the first sug-
gestion in any crawling animal of water habits is shown in the
relative lengths of the epipodial bones, as these bones are called.
Furthermore, cursorial or terrestrial habits are suggested by the
relative size of the smaller bone of the leg, that on the little-toe
side, the fibula. In birds, pterodactyls, and most running animals,
it disappears in part or wholly. In swimming animals it tends
to grow larger than the tibia, as will be conspicuously seen in the
paddle of the mosasaurs.

The bones of the wrist change in two ways: by becoming
cartilaginous, as in whales and salamanders, or by becoming more
firmly ossified and more closely united, as in the plesiosaurs. The
digits always are elongated, often extraordinarily so, either by the
elongation of individual bones or phalanges, or by the development
of new bones. These new bones, when they occur, are new growths,
not the reproduction of the old elements of fishes, and there may
be as many as twenty such new elements or phalanges in a single
digit. There is one marked exception among reptiles to this
hyperphalangy, as the increased number of phalanges is called, and
that is the turtles. As we have seen, in the elongation of the neck
7° WATER REPTILES OF THE PAST AND PRESENT

among turtles there never has been an actual increase in the num-
ber of vertebrae; so also in the elongation of the digits the normal
number of three in each digit has never been exceeded, except among
the river turtles, where there are four in the fourth digit—possibly
a relic of original conditions rather than the beginning of hyper-
phalangy; but the individual bones have become greatly elongated.
In living reptiles, birds and’: mammals of the land, the fifth toe is
always shorter than the fourth. In the seals, the sea-otter, and to
a less degree in the muskrat, the fifth toe has become elongated.
And the elongation of this toe is the first and most decisive indica-
tion of a webbed foot of strong propelling power among the aquatic
reptiles of the past, as exemplified especially by the proganosaurs.
Finally, in one order of extinct reptiles, the ichthyosaurs, there has.
been an actual increase in the number of digits, in some to as many
as nine in each paddle.

In addition to all these modifications of the skeleton, the bones
themselves tend to become softer and more spongy in aquatic
animals. The bones of the whale, as is well known, are very spongy
in texture, and those of the seals and sea-lions contain an unusually
large amount of oily matter. So, too, the bones of the extinct water
reptiles—of many of them at least—were more spongy than those
of their land relatives; and this is due in part perhaps to their
lessened use as muscular supports, in part perhaps to the necessity
of a lessened specific gravity. As a rule sea-animals need to be of
the same specific gravity as the water in which they live, or a little
less. The bones of the living sirenians, the manatees and dugongs,
so far from being light and porous, are unusually dense and solid.
The sirenians live habitually at the bottom of shallow waters, feed-
ing upon vegetable growths; and doubtless their bottom-feeding
habits account for the solidity of the bones. A whale would float ©
to the top, while a dugong would sink to the bottom, on the relaxa-
tion of all muscular movement. And we shall see that certain
reptiles in the past had in all probability like bottom-feeding habits,
because of the solidity of the bones of their skeletons.

Many birds and fishes have a peculiar ossification of the usually
tendinous outer covering of the eyeball, called the sclerotic mem-
brane. These ‘ossifications form a flattened or somewhat pro-
ADAPTATION OF LAND REPTILES TO LIFE IN WATER 71

jecting conical bony ring about the pupil of the eye. The individual
bones are flat and more or less imbricated plates, with some motion
between them. Accommodation for vision in reptiles, birds, and
fishes is not the simple process that it is in mammals, where it is
controlled by simple ciliary muscles which compress the lens, caus-
ing it to assume a more spherical or a more flattened form, thus
changing the focus. In reptiles accommodation is effected by the
compression of the eyeball by means of external muscles, elongating
it and causing its front part to expand or project. The imbricated
sclerotic plates permit this expansion and contraction of the eye-
ball. Under great internal or external air pressure the cornea, the
only unprotected part, must necessarily change its contour unless
some compensatory force is brought to bear to counterbalance it;
and this doubtless was the function of the sclerotic plates so com-
monly present in aquatic reptiles.

Among terrestrial reptiles there are not a few examples of the
ossification of such sclerotic plates, notably among the skink lizards.
Every known form of extinct reptiles of aquatic habit had them, and
even some of the subaquatic dinosaurs, like Diplodocus and Tracho-
don. One may say with assurance that it is impossible for any rep-
tile to become thoroughly adapted to aquatic life without acquiring
large and strong sclerotic plates.

Most land reptiles are or were covered by horny scales or bony
plates; the pterodactyls are the only order of terrestrial reptiles
with no such covering of which we have any evidence. Such
coverings are wholly unneeded for animals living in the water.
Not only are they unnecessary, but the increased resistance to the
water would be more or less detrimental to rapid swimming. It
is for these reasons doubtless that bony plates or horny scales dis-
appeared for the most part from the skin of all truly aquatic reptiles
and mammals.

The foregoing are the chief acquired characteristics of aquatic
air-breathing animals and especially aquatic reptiles in adaptation
to their new mode of life. The resemblances, sometimes striking,
thus brought about in animals of very different origin and remote
relationships have often been mistaken for evidences of kinship,
that is, direct inheritance from common ancestors. Such acquired
72 WATER REPTILES OF THE PAST AND PRESENT

resemblances in unrelated animals are known as parallel or con-
vergent evolution. It has often been difficult to distinguish
between convergent evolution and direct evolution, and difficulties
still perplex and trouble the student of natural history in every
branch of life. Not till all such problems are solved can we hope
to attain the true classification of animals and plants. The whales
a century ago were considered merely breathing fishes; the ichthyo-
saurs until a quarter of a century ago were supposed to be the
direct descendants of fishes; lizards and crocodiles were grouped
together in a single order; and salamanders were called reptiles
not very long ago.

Perhaps the reader will be able from the foregoing to under-
stand and appreciate better some of the difficulties that confront
the paleontologist in his attempts to solve the problems of past life;
to understand why he sometimes makes mistakes, for he has by
no means yet learned all the permutations of the skeleton in any
class of vertebrates, and is not sure that the laws he accepts are
not subject to modifications and exceptions. If he is truly scien- -
tific he hesitates long in prophesying or conjecturing.
CHAPTER VI
SAUROPTERYGIA

Very scanty are the early human records of those strange
reptiles known as the plesiosaurs. Were one to search through the
many works published during the latter half of the seventeenth
century and all of the eighteenth, devoted to “‘lapides petrifacti,”
“figured stones,” “‘reliquia diluvii,’’ or by whatever other fanciful
names fossils were known, here and there he would probably find
descriptions and figures of bones of these reptiles. It would hardly
seem that plesiosaurian bones could have been overlooked by the
curious, so abundant are they in many places. But there is no
such history of the early discovery of the plesiosaurs as there is of
the ichthyosaurs and mosasaurs. Their birth into human history
was very formal and proper, under the ministrations of a learned
doctor of science, the renowned Conybeare, of whom we shall
speak again. It was he, who with De la Béche, late Director of
the British Geological Survey, described for the first time, in 1823,
one of these reptiles, to which he gave the name Plesiosaurus,
meaning ‘“‘like a lizard.” He distinguished the plesiosaurs from
ichthyosaurs, with which it is possible that they had previously
been confounded, and gave a good description of considerable
material. Cuvier, a little later, gave a more complete description
of the same remains which had served Conybeare and De la Béche
for their original description, and for the first time made it evident
that fossil plesiosaurs were widely and abundantly distributed
over the earth. The closing sentence of Cuvier’s chapter devoted
to the discussion of these creatures in his Ossemens Fossiles was
really prophetic, not only of the many discoveries of the plesiosaurs
yet to be made, but of all other extinct animals as well: ‘I doubt
not that, in a few years it may be, I shal] be compelled to say that
the work which I have today finished, and to which I have given
so much labor is but the first glimspe of the immense creations of
ancient times.”

73
WATER REPTILES OF THE PAST AND PRESENT

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SAUROPTERYGIA 75

In quick succession there followed many other discoveries of
plesiosaurs, not only in England but elsewhere in Europe. The
famous English anatomist and paleontologist, Sir Richard Owen,
to whom we owe, perhaps, more than to anyone else our present
knowledge of these animals, the eccentric Hawkins of England, the
learned von Meyer of Germany, and, in later times, more especially
Seeley and Andrews of England, Fraas of Germany, Bogalobou
and Riabanin of Russia, as wel] as many others, have brought to
light during the past century many and varied forms of these sea-
reptiles. Blaineville in 1835 gave to the plesiosaurs an ordinal
rank under the class Ichthyosauria, and even the astute Owen
in 1839 united them with the ichthyosaurs as a suborder of his
Enaliosauria, or ‘‘sea-saurians.” He called them Sauropterygia, or
‘‘reptile-finned,” and these terms, Enaliosauria, Ichthyopterygia,
and Sauropterygia, have long persisted in works on natural his-
tory because of the prestige of Owen’s name. As we shall see later,
the plesiosaurs are really of remote kinship to the ichthyosaurs,
and there is no such natural group as the Enaliosauria. It often
takes years to distinguish between apparent and real relationships
among living organisms, and both of these groups of sea-saurians
have had a sorry experience in the treatment they have received
from nomenclators.

Perhaps because of the writings of Dean Buckland in his famous
Bridgewater Treatise, in large part a theological disquisition, though
of real scientific merit, the ichthyosaurs and plesiosaurs early
became widely and popularly known, and, even to this day, these
reptiles, together with the dinosaurs, first made known by Rev.
Dr. Mantell, are often supposed to be the most typical and horrid
of monsters. Many and fabulous are the tales that have been
told of them in literature both grave and gay. The preacher
adduced them as evidences of the great world-catastrophe told in
biblical history, and the German student sings of them to the tune.
of the ‘‘Lorelei’’:

Es rauscht in Schachtelhalmen, verdachtig leuchtet das Meer;

Da schwimmt mit Thrinen in Auge ein Ichthyosaurus einher.

Ihn jammert der Zeiten Verderbniss, denn ein sehr bedenklicher Ton
War neuerlich eingerissen in der Liasformation.
76 WATER REPTILES OF THE PAST AND PRESENT

Der Plesiosaurus, der alte, der jubelt in Saus und Braus;
Der Pterodactylus selber flog jungst betrunken nach Haus.
Der Iguanodon, der Liimmel, wird frecher zu jeglicher Frist;
Schon hat er am hellen Tage die Ichthosaura gekiisst.

We now know that they were not the monsters of horrid mien
that they were once supposed to be: the largest plesiosaurs, were
they living today, would find unopposable foes in the vicious and
cruel crocodiles. They were relatively stupid and slow, cruel
enough to the smaller creatures, but of limited prowess. But in
structure and habits they are among the most remarkable of all
the animals of the past or present.

Although their remains are among the most abundant and
widely distributed of all fossil reptiles, the plesiosaurs as a whole
are less perfectly known than either the ichthyosaurs or the mosa-
saurs, and it has been within a comparatively few years only that
an approximately complete knowledge of any form has been
obtained. This is partly due to the fact that the order comprises
vastly. more kinds, more species, genera, and families than does
any other order of marine reptiles; partly because their remains,
though widely distributed over the earth, and in rocks of many
geological epochs, are seldom found completely preserved; usually
specimens comprise only a few bones or single bones, and complete
skeletons are rare. Were there but few kinds, the many specimens
discovered would mutually supplement each other, finally com-
pleting our knowledge; but the fragments of many kinds only add
to our confusion. Nevertheless, because the plesiosaurs lived so
long in geological history, their remains are found in rocks of many
different kinds, and since it is improbable that any of them had
great specific longevity, it is very probable that all these described
species, or most of them, often made known from single bones, will
eventually be found to be distinct, and that many more wil] be
added to them. It does not seem improbable that within the next
forty or fifty years not less than a hundred species of plesiosaurs
will have been discovered in North America alone. At the present
time perhaps that many have been described from the whole world.

When Blaineville gave the name Plesiosauria to the aquatic
reptiles described by Conybeare, Cuvier, and others, he had no
SAUROPTERYGIA 77

knowledge of others of an intermediate kind between them and
land reptiles. His group-term then can be properly applied only
to the truly aquatic forms, and Owen’s name Sauropterygia becomes
available in a wider sense to include all the known types belonging
to the order of which the plesiosaurs form a part. Of this order
then there are two clearly marked divisions or suborders, the
Plesiosauria and the Nothosauria, the former having a complete
aquatic adaptation, the latter only a partial one. While the two
suborders are evidently allied, some authors have suggested that
their differences are only familial; others have thought that they
are really orders. We shall see how close the relationships are.

PLESIOSAURIA,

It was Dean Buckland who facetiously likened the plesiosaurs
to a snake threaded through the shell of a turtle, and the simile
was not an inapt one in his day. The vernacular designation of
them—long-necked lizards—conveys the same impression of their
chief peculiarity, but the name is less applicable than it once was,
since recent discoveries have brought to light forms with a relatively
short neck. 4

Though the plesiosaurs are nearly perfectly: adapted to an
aquatic life, the adaptation was, in many respects, of a very differ-
ent kind from that of the ichthyosaurs—so very different that we
have not yet quite finished conjecturing as to the habits of the
living animals. As already suggested in the popular name, the
most striking characteristic of the typical plesiosaurs, the one which
suggested to Buckland his frequently quoted simile, is the ofttimes
enormously long neck, proportionately longer than that of any other
known creatures of the past or present. In other truly aquatic
animals the neck is actually shortened in the acquirement of a fish-
like shape, and the number of bones composing it reduced. In the
Sauropterygia the neck is usually longer than any truly land ani-
mals ever possessed, the longest-necked forms having as many as
seventy-six vertebrae in the cervical region. The elongation of the
neck among mammals is always due to an increase in the length of
the individual bones, never to an increase in the number from seven,
with but a single exception—a South American sloth which has
78 WATER REPTILES OF THE PAST AND PRESENT

nine cervical vertebrae. The long neck of birds is due both to an
increase in the length of the individual vertebrae and to an increase
in their number, to as many as twenty-one. But the elongation of
the neck among plesiosaurs was very variable indeed; sometimes
it was ten or twelve times the length of the head, at other times it
was even shorter than the head. And the number of bones com-
posing it was also extremely variable, scarcely any two species
having the same, the known extremes being seventy-six and
thirteen. In Elasmosaurus platyurus, for instance, the longest-
necked plesiosaur known, the head was two feet in length, the
neck twenty-three, the body nine, and the tail about seven; on the
other hand, in the shortest-necked plesiosaur known, Brachau-

 

Fic. 32.—Skeleton of Trinacromerum osborni, a Cretaceous plesiosaur, as mounted
in the University of Kansas Museum.

chenius Lucasi, the head was two and one-half feet in length, the
neck less than two feet, and the body about five; the length of the
tail is unknown.

Not only was the number of vertebrae so extraordinarily
increased in many plesiosaurs, but in the longest necks the verte-
brae themselves, as in birds, were more or less elongated, especially
the posterior ones, which may be six or seven times the length of
the anterior ones. Not only was the neck of such great length
in many plesiosaurs, but it also tapered very much toward the
head.

The vertebrae are always biconcave, but the cavities are shallow,
saucer-like, sometimes almost flat at each end, and very different
from the conical fish-like cavities of ichthyosaurian vertebrae.
79

SAUROPTERYGIA

 

IMesorsatd snoadeje1_g 1addy ure ‘snankjoj¢ snanvsousyiy JO Uoryes0oj|say—

ff ‘org

 

 
80 WATER REPTILES OF THE PAST AND PRESENT

Often the vertebrae are short throughout the vertebral column,
sometimes the posterior cervicals and the dorsals are elongated
and very robust. The trunk or body proper was never much
elongated in the plesiosaurs, having only from twenty-five to thirty
vertebrae. The tail was always shorter than the trunk, and it
tapered rapidly to the extremity; in some specimens it has been
observed to turn up slightly near the extremity, as though for the
support of a small terminal fin.

The ribs in the cervical region are short, but so locked together
posteriorly as not to permit much lateral motion. They are

 

Fic. 34.—Cervical vertebrae, from the side and behind, and dorsal vertebra from
in front of Polycotylus, a Cretaceous plesiosaur: az, anterior zygapophysis; pz, pos-
terior zygapophysis, 7, 7, r, cervical ribs; d, articulation of dorsal rib.

sometimes double-headed in the neck, sometimes single-headed, but
both heads when present articulate or are attached to the body of
the vertebrae, distinguishing them at once from those of other
animals, except the ichthyosaurs. In the dorsal region the ribs
are attached high on the arch to the extremity. of the stout trans-
verse processes by a single head, very much as they are in some
cetaceans, and quite unlike the condition in any other known
reptile. They end freely below, having no attachment to a
breast bone or other. bony parts. Because of their shape and
position as frequently found, the body in life must have been flat-
tened from above downward, and broad; indeed, this shape is
SAUROPTERYGIA 81

quite certain because of the very broad expanse of the coracoids,
between the articulations of the front legs.

The shoulder girdle or pectoral arch is strangely unlike that of
any other reptiles. There is no breast bone, since the breast bone

 

Fic. 35.—Pectoral girdle of Trinacromerum from above: ic, interclavicle; cl,
clavicle; sc, scapula; c, coracoid.

is a comparatively late development in reptiles, not appearing,
probably, until after the plesiosaurs had begun their existence.
Taking the place of the sternum, the very large and broad coracoids
82 WATER REPTILES OF THE PAST AND PRESENT

join each other in the middle, forming a sort of subdermal
armor on the under side of the body in front. In some of the
largest plesiosaurs these two bones measured together about six
feet in length by four in width. Though so very large they are
thick only in front between the articulations of the forelegs. The
shoulder-blades are much reduced in size and are extraordinarily
modified. The blade proper, that is, that part extending backward
and upward, is narrow and small, affording but little surface for
the attachment of muscles. On the inner side, extending toward
the middle in front of the coracoids, there is another projection,
often broad and large, to which was attached the clavicles when
present, and often this projection met its mate of the opposite
scapula in the middle in front of the coracoids in a broad union.
The clavicles or collar-bones are small and thin, and sometimes
absent; they also are united in the middle posteriorly with the
coracoids when the scapula did not intervene. And the inter-
clavicle also is sometimes wanting. Altogether the pectoral bones
form a very large, broad, and concave trough inclosing the whole
of the under side of the anterior part of the body. This extensive
surface must have furnished attachment to stout and strong muscles
controlling the downward and inward motion of the paddles.

There is a well-developed sacrum of three vertebrae for the
support of the pelvis or hip bones. The reason for its persistence
in animals so thoroughly adapted for life in the water will be under-
stood later. The ilium is slender; it was attached to the sides of
the sacrum by ligaments, only, not forming a firm union, but
strong nevertheless. The pubes and ischia, the other bones of the
pelvis on the under side of the body, like the corresponding bones
of the pectoral girdle, were enormously enlarged, forming great
flat, bony plates.

Besides these large bony plates of the shoulder and pelvic
girdles, the short abdominal region was inclosed by numerous series
of strong ventral ribs, that is, overlapping rod-like bones on each
side, connected with a central piece. It will be seen that the whole
under side of the body, from the base of the neck to the base of the
tail, was well protected by bones, rigid and unyielding in front and
behind, flexible for a short space below the abdomen; . this surface,
SAUROPTERYGIA 83

however, was not flat like the under shell of a turtle, but rounded
from side to side.

tr ae
Pye bie

\\\
\

Ean es cea lias

=

 

Fic. 36.—Pelvic girdle from above of Trinacromerum osborni, an Upper Cretaceous
plesiosaur: , pubis; is, ischium; 1, ilium.

Many of the characteristics of the limbs of thé plesiosaurs are
peculiar to themselves; others they had in common with other
84 WATER REPTILES OF THE PAST AND PRESENT

aquatic reptiles and mammals. The paddles resemble those of the
ichthyosaurs more nearly than those of any other reptile, and it
was doubtless this superficial resemblance which so long deceived
the early anatomists as to the affinities of the two orders. Unlike
all other aquatic animals, however, the plesiosaurs have the hind
limbs nearly or quite as large as the front ones, and they doubtless
were equally effective in function. The humerus and femur are
always elongate, though broad and massive. In no other aquatic
animals, save the marine turtles, do we find these bones relatively

 

Fic. 37.—Pelvic girdle of Elasmosaurus: p, pubis; is, ischium; ii, ilium

so long and strong; they are very short in the cetaceans, the sire-
nians, the ichthyosaurs, mosasaurs, thalattosaurs, and the marine
crocodiles, in front at least. The strong muscular rugosities of
the plesiosaurian bones are very suggestive of powerful swimming
muscles.

The bones of the forearms and legs, the wrists and ankles are
all polygonal platelets of bones, closely articulating with each other.
The finger and toe bones have a more elongated, hour-glass shape
than those of the ichthyosaurs, resembling more nearly those of the
SAUROPTERYGIA 85

mosasaurs, indicating a greater flexibility than the ichthyosaurs
possessed. The ichthyosaur paddles must have been quite like
the fins of fishes in function, while doubtless those of the plesiosaurs
were capable of a more varied use, as indeed was required of them.
Their articulation with the trunk was more of a ball-and-socket

 

Fic. 38.—Paddles of Plesiosaurs: A, right hind paddle of Thaumatosaurus, after
Fraas; B, right hind paddle of Trinacromerum; C, right front paddle of same indi-
vidual; f/, femur; fb, fibula; ¢, tibia; 4, humerus; 7, radius; w, ulna.

joint than in the other reptiles, showing possibility of considerable
rotation on the long axis, and an antero-posterior propelling action.
The paddles were certainly more powerful than those of any other
aquatic air-breathing animals. There were no additional digits,
all plesiosaurs having neither more nor less than five in each hand .
and foot. Hyperphalangy was sometimes carried to an excessive
86 WATER REPTILES OF THE PAST AND PRESENT

degree, some digits of some species having as many as twenty-four
bones, a larger number than has been observed in any other air-
breathing vertebrate.

   

Fic. 39.—Pectoral girdle (in part) and \4
front paddles of Elasmosaurus (after Riggs): 4
sc, scapula; h, humerus; cor, coracoid; 1, q 3
radius; #, ulna. BY ¥
q 8
%

In Fig. 38 on p. 85 are shown two paddles, the front and
hind paddles of a single individual of a very specialized ple-
siosaur from the Upper Cretaceous of Kansas (Trinacromerum).
The long arm and thigh bones are followed by remarkably short and
SAUROPTERYGIA 87

broad bones in place of the elongated forearm and leg bones of the
land reptiles. Not only are these bones much broader than they
are long, but there have been developed additional bones back of
them in the same row—new bones which have no counterpart in
any terrestrial reptiles. In the first of the three figures is shown
a hind paddle of one of the earliest known plesiosaurs, Thauma-
tosaurus, from the lower part of the Jurassic of Germany. It will
be seen here that the tibia and fibula are much more elongated than
in Trinacromerum, and much more like the leg bones of land reptiles.
A still more primitive stage in the evolution of the swimming paddle
of the plesiosaurs will be seen in Fig. 48 on p. 99, the possibly
ancestral, amphibious nothosaur. Here the tibia and fibula, while
relatively very much shorter than in any land reptile, still have,
together with all the other
bones of the leg, a terrestrial
or amphibious type. In Fig.
39 is seen the front paddles
of the long-necked Elasmo-
saurus, which, though one of

the latest of all P lesiosaurs in Fic. 40.—Skull of Elasmosaurus from the
geological history, has the side: pm, premaxilla; m, maxilla; po, post-
structure of its paddles some- orbital; j, jugal.
what intermediate between
that of the earlier Plesiosawrus and the later Trinacromerum.
The skull of the long-necked plesiosaurs is surprisingly small
in comparison with the remainder of the skeleton, often very
snake-like in shape, though very un-snake-like in structure. The
short-necked plesiosaurs had often a relatively larger skull, in Plio-
saurus, for instance, more than five feet long, sometimes rather
broad and short, sometimes remarkably Jong and slender. The
external nostrils were situated far back, very near the eyes, and
were very small. The eyes, of considerable size, though by no
means so large as those of the ichthyosaurs, were directed laterally,
and were provided with a ring of bony sclerotic plates—rather
smal] and weak ones, however. The quadrate bones—bones pecu-
liar'to the reptiles and birds—to which the lower jaws are articu-
lated, are, as in the ichthyosaurs and crocodiles, rigidly fixed and

 
88 WATER REPTILES OF THE PAST AND PRESENT

immovable. The lower jaws, always rather slender, are firmly
united in front, sometimes for a Jong distance, as in the modern
gavials. The teeth of the broad-headed plesiosaurs are long,
slender, pointed, and recurved, of a murderously cruel shape; they
are deeply implanted in sockets, and number from twenty to
thirty on each jaw above and below. There are no teeth on the
bones of the palate, such as the mosasaurs possessed. The slender-
jawed, gavial-like plesiosaurs have more numerous, but smaller
teeth. The surface of the skull on each side behind, for the attach-
ment of the muscles closing the mandibles, is of great extent; in
some this surface is increased by a high, thin crest in the middle,
as in strongly carnivorous animals, all of which give conclusive
evidence of the powerful muscles used in biting and seizing. There
is but one temporal opening on each side, as in the ichthyosaurs

 

Fic. 41.—Skull of Trinacromerum from the side: ang, angular; d, dentary; pm,
premaxilla; po, postorbital; 7, jugal; sur, surangular.

and the mosasaurs, whereas the crocodiles, thalattosaurs, phyto-
saurs, etc., have two. The brain cavity of all plesiosaurs is small,
though the cavities of the internal ears, the semicircular canals at
least, are large. The semicircular canals in vertebrates have little
or nothing to do with the function of hearing; they serve rather for
equilibration, for the co-ordination of muscular movement; possi-
bly we may infer from their large size in the plesiosaurs that they
were not at all clumsy in their movements. There is a large open-
ing for the pineal body, the so-called eye in the roof of the brain
cavity, though its possession does not necessarily imply the pos-
session of a functional organ.

The Plesiosauria included some of the largest aquatic reptiles
that have ever existed, equaled, perhaps, though not exceeded,
by. some of the extinct crocodiles. The largest known are probably
SAUROPTERYGIA 89

those of the Kansas chalk, or the Jurassic of Wyoming, which
probably reached a length of nearly or quite fifty feet, of which the
neck formed about one-half. Some of them had paddles more than
six feet in length. The head of the largest was about five feet in
length, or about the size of that of the largest known ichthyosaurs
and mosasaurs. The smallest known adult plesiosaurs were nearly
ten feet in length. The teeth of the largest and most carnivorous
plesiosaurs sometimes measure four inches in length.

As is the case with both the ichthyosaurs and mosasaurs,
skeletons of plesiosaurs have been discovered with nearly all their

 

ee

 

 

 

Fic. 42.—Restoration of Trinacromerum, a Cretaceous plesiosaur; length about
ten feet.

bones in their relative positions, and with impressions of skin and
outlines of body made before decomposition. Though our knowl-
edge of the external appearance of the plesiosaurs when alive is
perhaps not as full as we could wish, it is sufficient to give us a fairly
good conception of what the animals really were. The skin was
smooth and bare, without scales or plates of any kind, and Dames
has described a terminal or nearly terminal fleshy dilatation of the
tail, forming a sort of caudal fin, which may have aided as a steering
apparatus. Mounted skeletons are preserved in a few museums,
notably the British Museum, the American Museum of New York
City, and the museum of the University of Kansas. Many nearly
go WATER REPTILES OF THE PAST AND PRESENT

complete skeletons, however, preserved as they were found in the
matrix, are shown in various museums.

With these principal facts regarding the structure, size, and
external form of these animals we may venture to draw certain
conclusions, or at least to offer certain conjectures as to their habits
in life.

Because of the rigid structure of the jaws, united in front and
incapable of any lateral movement posteriorly, quite as are the
jaws of crocodiles, we are sure that prey of any considerable size
could not have been swallowed whole. The crocodiles tear away
portions of the flesh of their victims by quick, powerful jerks, and
it is very probable that the flat-headed plesiosaurs tore their food
apart in the same manner. In these kinds the teeth are much
larger and more irregular in size than are those of the long-snouted
plesiosaurs, and their use was certainly as much for tearing as
for seizing. There are the same differences between the size of
the head and the size of the teeth among the various plesiosaurs
that there are among the modern crocodiles and gavials. While
the crocodiles seize and déstroy even larger prey, drowning and
tearing their victims to pieces, the gavials are more exclusively
fish-eating, for which their small, sharp, and more numerous teeth
especially fit them. Their food, of small size, is swallowed entire,
and they are comparatively harmless, so far as animals of consid-
erable size are concerned.

The long neck, the thickset body, and short, stout tail are not
at all what we should expect to find in quick-swimming animals.
We may therefore assume that the motions of the plesiosaurs
through the water were more turtle-like than fish-like. The tail,
even though provided with a terminal, fin-like dilatation, was of
little use in the propulsion of the body, since the range of its move-
ments was restricted; it possibly served in a measure as a steering
organ, a rudder. The large, freely movable paddles must have
been effective organs of locomotion, and this function accounts for
the relatively large size of the posterior pair, and the firm union of
the pelvis with the vertebral column through the sacrum. With
the hind limbs used as oar-like organs, a firmer union with the
skeleton was required than the soft yielding flesh would permit.
SAUROPTERYGIA gI

At the same time this union was ligamentous only, not bony and
unyielding, since the limbs were never used to support the body
upon the ground;. and it is of interest to observe that the ilia are
directed, not upward and forward, but upward and backward to
the sternum, precisely the position that would be expected with the.
force or thrust coming from behind, and not below the yielding
ligaments. Were the tail longer and more powerful, the hind limbs
would have been smaller and weaker, of use chiefly in equilibration,
involving the loss of any connection with the vertebral column and
the disappearance of the sacrum. It is of interest, finally, to
observe that many of the slender-jawed plesiosaurs had a relatively
short neck; they were doubtless more distinctively fish-eating in
habit, and possessed greater speed. That the limbs of plesiosaurs
were powerful propelling organs is also conclusively proved by their
structure. Quite unlike all those animals whose locomotion in the
water is chiefly effected by the tail, the humeri and femora, the
upper arm and thigh bones were elongated, and not shortened.
They form the rigid and stout handles of oars whose blades are the
thinner, flexible forearm, wrist, and fingers, or the corresponding
foreleg, ankle, and toes. No other purely aquatic reptiles, save
the turtles, which likewise are of the oar-propelled type, have
elongated arm and thigh bones.

Textbook illustrations of the plesiosaurs usually depict the
necks, like those of the swans, freely curved, and a popular scientific
article in one of our chief magazines a few years ago depicted one of
them with the neck coiled like the body of a snake. One noted
paleontologist, indeed, not many years ago described the plesiosaurs
as resting on the bottom in shallow waters with the neck uplifted
above the surface viewing the waterscape! And when we con-
sider the fact that some species of the elasmosaurs had a.neck not
less than twenty feet in length, such a flexible use of it would not
seem improbable. But the plesiosaurs did not and could not use
the neck in such ways. They swam with the neck and head, how-
ever long, directed in front, and freedom of movement was restricted
almost wholly to the anterior part. The posterior part of the neck
was thick and heavy, and could not have been moved upward or
downward to any considerable extent and not very much laterally.
92 WATER REPTILES OF THE PAST AND PRESENT

From all of which it seems evident that the plesiosaurs caught their
prey by downward and lateral motions of their neck, rather than
by quick swimming.

 

Fic. 43.—Gastroliths and bones of an undetermined plesiosaur from the Lower
Cretaceous of Kansas.

About thirty years ago, the late Professor Seeley, a well-known
English paleontologist who devoted much attention to the study
of these reptiles, found with the remains of a medium-sized plesio-
saur nearly a peck of smoothly polished, rounded, and siliceous
SAUROPTERYGIA 93

pebbles. He believed that their occurrence with the skeleton was
not accidental, but that they had been intentionally swallowed
by the animal when alive, and formed at its death a part of its
stomach contents. Even earlier than this the same habit had been
noticed. Nearly at the same time that Seeley mentioned the
peculiar discovery he had made the present writer found several
specimens of plesiosaurs in the chalk of western Kansas with which
similar pebbles were associated, an account of which was given
soon afterward by the late Professor Mudge. Since then numerous
like discoveries have made it certain that the plesiosaurs usually, if
not always, swallowed such pebbles in considerable quantities, for
what purpose we do not yet feel sure; one can only hazard a guess.
The small size of the pebbles, or gastroliths, as they have been
called, a half-inch or less in diameter, found with skeletons of large
size, indicate much more complete digestion of the hard parts of
their food than is the case with many other reptiles; no solid sub-
stance of size could have passed out of the plesiosaur stomach, and
such is the case with the modern crocodiles, which have a like habit
of swallowing pebbles. That the plesiosaurs picked up these sili-
ceous pebbles, sometimes weighing a half-pound, accidentally with
-their food is highly improbable; they surely had something to do
with their food habits. It is not at all unreasonable to suppose
that the plesiosaurs, because of their comparative sluggishness, fed
upon anything of an animal nature, whether living or dead, which
came in their way; that carrion, squids, crustaceans, and fishes
were all equally acceptable; they were probably largely scavengers |
of the old oceans. Barnum Brown found among the stomach
contents of a plesiosaur fragments of fish and pterodactyl bones,
and cephalopod shells. Gallinaceous birds, most of which have the
same pebble-swallowing habit, havea thick-walled muscular stomach
or gizzard, in which the pebbles serve as an aid in the trituration
of food. Modern crocodiles, with the same pebble-swallowing
habit, have a thick-walled muscular stomach, gizzard-like, though
of course not as large as in birds; and the same habit has been
noted by Des Longchamps in the ancient teleosaur crocodiles.

It is hardly possible yet to decide whether or not the plesiosaurs
were denizens of the open oceans for the most part, far from land.
94 WATER REPTILES OF THE PAST AND PRESENT

That many of them were rovers is quite certain. With the skeleton
of a large plesiosaur found some years ago in western Kansas, there
were many siliceous pebbles which could have come only from the
. shores of the old Cretaceous seas about the Black Hills, hundreds
of miles distant. Some of the pebbles are red quartzite, quite
identical with that of the bowlders brought to Kansas millions of
years later by the glacial drift from outcroppings near the northern
line of Iowa. The bones of plesiosaurs are often found in deposits
believed to be of deep-water origin. But they are also found in
Kansas associated with the remains of small turtles, flying reptiles,
and birds which could only have lived near the shores. Indeed,
their remains have often been found with those of strictly fresh-
water animals which had been brought down by the floods to the
seas. Their wide but rather sparse distribution in all kinds of
marine sediments would rather indicate that they were at home far
out in the tempestuous ocean or near the shores in protected bays,
though probably they preferred the shallow-water littoral regions.
One conclusion is quite justified: they were not gregarious, as were
~ the ichthyosaurs.

It is not certain that the plesiosaurs were viviparous, though
there are good reasons for the belief that they were. Remains of
two embryos were found years ago in England associated in such
a way that it is reasonable to suppose they were unhatched young,
though embryos have never yet been found associated with skele-
tons of adults, as have those of ichthyosaurs in numerous instances.
Bones of young, often quite young, plesiosaurs, are frequently
found in shallow-water deposits, and if the young were actually
born alive they must have swum freely in the open waters while
yet of very tender age. Rather singularly, however, the remains
of these young plesiosaurs always occur as isolated bones.

In geological range the plesiosaurs were very persistent, extend-
ing through nearly all the Mesozoic. They began their career as
fully evolved plesiosaurs, so far as we now know, near the close of
the Triassic period, and reached their culmination in the Upper
Cretaceous, but survived to the close of that period. In the begin-
ning of their career they were associated with the marine crocodiles
and the ichthyosaurs, but outlived them to find companions and
probably enemies in the huge and voracious mosasaurs of the later
SAUROPTERYGIA 95

Cretaceous times. At no time do they appear to have been especially
numerous, nor does it seem probable that they were ever a domi-
nant type of marine vertebrate life, though their remains occur
everywhere that marine deposits of the Jura and Cretaceous are
known. Indeed, it may be said with almost certainty that rocks of
these ages and of that character everywhere in the world contain
fossil plesiosaurs. Their bones have been made known from
Europe, Asia, Africa, Australia, and North and South America.
From North America thirty or more species have been described
from New Jersey, Alabama, Mississippi, Texas, Arkansas, Kansas,
Nebraska, Colorado, New Mexico, Wyoming, North and South
Dakota, California, etc.

The cause of their final extinction no one knows, nor can we
conjecture much about it with assurance. That climatic conditions
became unfavorable for them is highly improbable, considering
their cosmopolitan habits; they were not discriminating in their
environments. After successfully withstanding their fiercest foes,
the ichthyosaurs, crocodiles, and mosasaurs, and large carnivorous
fishes, it does not seem probable that they would succumb to lesser
enemies, though it may be that they were finally attacked success-
fully, not in the fulness of their strength as adults, but while young,
by more insidious enemies. More probably after their long life of
millions of years they had grown old, as everything grows old, and
had become so fixed and unplastic in their structure and habits
that even slight causes were at last their undoing. When we shall
have bridged over that still imperfectly known transition period
between the great Age of Reptiles and the greater Age of Mammals
we shall have learned more definitely some of the causes of the
extraordinary revolution in vertebrate life that then occurred.
The plesiosaurs went out with nearly all of their kind, the mosa-
saurs, the pterodactyls, the dinosaurs; and, so far as we now know,
their places in the sea, land, and air were not immediately taken
by any other creatures.

NOTHOSAURIA

A few years after the discovery of the plesiosaurs by Conybeare,
the remains of animals of allied kinds were found in the Triassic
rocks of Bavaria. At first they were supposed to be those of true
96

WATER REPTILES OF

THE

PAST AND PRESENT

 

 

 

 

 

Fic. 44.—Nothosaurus; restoration after E. Fraas; landscape by Dorothy Williston
SAUROPTERYGIA 97

plesiosaurs, and even the astute Cuvier was not very clear about
them. Cuvier was the first to call attention to them, expressing
the opinion that some of the fossils were of previously unknown
animals allied to the crocodiles, lizards, and plesiosaurs. It was
von Meyer, however, who first introduced a nothosaur to the
scientific world under the name Conchiosaurus. A year later
Count George of Miinster described other forms under the name
Nothosaurus, meaning ‘‘false lizard.” Count von Miinster was a
most zealous collector of the fossils of the Triassic deposits of
Bavaria, amassing, after thirty years of active and enthusiastic
labor, a very large amount of material, which, at his death, was
purchased by the King of Bavaria and placed in the hands of von
Meyer for study. Von Meyer was to Germany what Owen was to

 

Fic. 45.—Head and neck of Nothosaurus; photograph of specimen in the Sencken-
berg Museum, from Dr. Dreverman.

England, a man of deep learning, having an extensive knowledge
of comparative anatomy, and being thorough and critical in his
work. His descriptions and illustrations of these rich collections
made by von Miinster are masterpieces of scientific thoroughness.
He recognized in Nothosaurus and other allied forms from the
Bavarian Triassic a distinct group of semiaquatic reptiles allied to
the plesiosaurs, and his conclusions have never been gainsaid. In
more recent years additional remains of these animals from Bavaria
and other places in Europe have been described, but none are
known from other parts of the earth, or from other than Triassic
rocks. Altogether about ten genera and about twice as many
species have been described, probably all belonging in one family,
and all by common consent now classified with the Sauropterygia.
98 WATER REPTILES OF THE PAST AND PRESENT

The Nothosauria were much smaller reptiles than the plesio-
‘saurs, none of them perhaps exceeding the size of the smallest known
plesiosaurs. They were semiaquatic in habit, with many curious

 

Fic. 46.—Pectoral girdle of Nothosaurus, from
photograph by E. Fraas: icl, interclavicle; ci,

clavicle; sc, scapula; cor, coracoid.

resemblances to other
semiaquatic reptiles of
a later time known, as
the dolichosaurs. The
neck is more or less
elongated, having about
twenty vertebrae in the
longest-necked forms;
the body is moderately
long, and broad, and
the tail is relatively
short. The vertebrae
and ribs are quite like
those of the plesiosaurs,
that is, the vertebrae
are gently concave at

each end, and the dorsal ribs are attached by a single head to the
transverse process high up on the arch; the cervical ribs are double-
headed, precisely like those of the older plesiosaurs, one of the char-

acters which insistently proves
the relationships of the two
groups. The bones of the shoul-
ders (Fig. 46) also have many
resemblances to the extraor-
dinary ones of the plesiosaurs,
though they are much less
specialized. There was no
sternum; the coracoids are
large, though very much
smaller than those of the plesi-
osaurs.

 

Fic. 47.—Pelvic bones of Nothosaurus:
i, ilium; ac, acetabulum; #, pubis; 7s,
ischium. (After Andrews.)

The collar-bones are large and strong, joining each other

in front of the coracoids and firmly united with the shoulder-
blades at the outer extremity. Four vertebrae are united to form
a sacrum, and their union with the hip bones (Fig. 47) was much
SAUROPTERYGIA 99

firmer than was the case with the plesiosaurs. The limbs are
elongated, but it will be observed in the figures (Fig. 48) that the
radius and ulna, tibia and fibula, that is, the bones of the forearm
and of the leg proper, are relatively very short as compared with
the humerus and femur, a sure indication of the beginning of
aquatic habits. The toes and fingers were doubtless webbed, and
there was no increase in the num-
bers of bones in the digits, so
conspicuous in the _plesiosaurs.
The external nostrils are large, but
are not situated so far back near
the eyes as in the plesiosaurs.
There is a large pineal opening in
the top of the skull, as in the plesi-
osaurs, but no sclerotic or bony
plates have been observed in. the
eyes. They had ventral ribs like
those of the plesiosaurs.

No impressions of scales or
bony plates have ever been found
with the remains of the notho-
saurs, and it is the belief that the
skin was bare. A good idea of
their general appearance will be
gained from the accompanying
restoration adapted from that of Fic. 48.—Legs of Lariosaurus bal-
Professor Fraas (Fig. 4. 4) and the %@m, an Upper Triassic nothosaur: h,

: humerus; +, radius; u, ulna; 2, inter-
restoration of the less highly media 4, cine: f, fen
specialized Lariosaurus, made fibula; ¢, tibia; a, astragalus; c, cal-
from a very complete skeleton in caneum. (After Abel.)
the Frankfort museum (Fig. 49).

It has been thought that these nothosaurs, so intermediate in
structure between the true plesiosaurs and land reptiles, were the
actual ancestors, but this is rather doubtful. It is probable that
they were only very closely akin to the real ancestors, since in some
ways they had become specialized too much, and, as we have

. already explained, highly specialized characters or organs can never

 
100 WATER REPTILES OF THE PAST AND PRESENT

 

 

 

 

Fic. 49.—Lariosaurus balsami
SAUROPTERYGIA IOL

go back to their earlier condition. The nothosaurs do prove
beyond all possibility of doubt that the plesiosaurs were at least
the descendants of animals closely allied to them, so closely, indeed,
that it is doubtful whether we could distinguish external differences
were all of them actually living at the present time.

We have repeatedly seen that all aquatic animals have some
or all the bones of the limbs shortened, and it is of interest to
observe that the early plesiosaurs had longer forearm and foreleg
bones than the later ones, just as we have seen was the case with the
early ichthyosaurs. It would seem probable that all the early
plesiosaurs had long necks, though some of the late ones in Cre-
taceous times had relatively short necks, shorter even than the
known nothosaurs possessed.

The nothosaurs doubtless lived about the shores of the ancient
seas, spending much of their time in the water, leaving it perhaps
when hard pressed by their enemies, as do some modern reptiles,
or to rear their young. The teeth of the nothosaurs are long
and slender in front, shorter behind. The animals must therefore
have been. carnivorous in habit, feeding probably upon such fishes
as they could catch, and the various invertebrates which live in
shallow water, The structure of the jaws and their attachments
are quite as in the plesiosaurs, proving that they could not have
swallowed large objects; but the skull is broader and flatter than
that of most plesiosaurs, indicating habits not unlike those of the
modern alligators and crocodiles.

Some time we shall doubtless find remains of nothosaurs or
nearly allied animals elsewhere than in Europe, but probably not
from later deposits than the Triassic. So far as we now know, their
geological range and geographical distribution were much restricted;
they evidently wholly died out shortly after the plesiosaurs appeared

’ \
CHAPTER VII
ANOMODONTIA
LYSTROSAURUS

Over a large area of South Africa, chiefly along the Orange
River and its tributaries, there is an extensive series of deposits
many hundreds of feet in thickness, usually called the Karoo beds,
which, for more than fifty years, have been widely famous among
scientific men for the many and remarkable vertebrate fossils
which they have yielded. These deposits seem to represent the
whole of the vast interval of time from the Carboniferous to the
Jurassic, that is, the whole of the Permian and Triassic, though
not many fossils have been found in the lowermost strata. Among
the fossils of the lower strata are those of the strange creatures
described in the following pages as Mesosaurus. From the deposits
representing the Upper Permian and the Triassic the fossils that
have been obtained are both abundant and diverse. Unfortu-
nately, however, of the scores of forms that have been discovered
few are known completely, and still fewer are known sufficiently
well to enable us to picture the living animals. -

From the Upper Permian Karoo rocks two orders of reptiles
have been recognized, the Cotylosauria, represented by more
specialized forms than those from the Lower Permian of North
America; and the order or group called by Broom the Therapsida.
While the forms of this latter group have certain definite structural
relationships with each other, they show so great a diversity among
themselves that, when they shall be better known, it will be
found necessary perhaps to separate them into several distinct
orders.

At least five groups of the Therapsida are now recognized by
Broom, the Dromasauria, Dinocephalia, Anomodontia, Thero-
cephalia, and Theriodontia. Of all these the members of the
last-mentioned group have attracted the greatest interest among

102
ANOMODONTIA 103

geologists and naturalists, because of their intimate relationships to
the mammals—so intimate, indeed, that they seem almost to bridge
over the interval between the two classes. From higher Karoo
beds primitive representatives of the more crocodilian types have
been discovered, forms which seem to be the beginning of that
order described on later pages as the Parasuchia.

It would lead us too far astray to mention even, let alone
describe, the many forms of reptiles that have been discovered
in the Karoo beds; nor indeed is it possible for anyone who
has not attentively studied their remains to get a very clear con-
ception of many of them, so incompletely have they been made
known.

Doubtless from among all these diverse forms there have been
not a few which sought wider opportunities in the water, but, if so,
we have as yet very little knowledge of them. One form only, so far
as the writer is aware, has been credited with aquatic habits, a
remarkable reptile belonging to the group originally called by
Sir Richard Owen, the Anomodontia, a word meaning ‘‘lawless
teeth,” and. to the genus Lystrosaurus, also described by the same
noted paleontologist. A restoration of the skeleton of Lystro-
saurus has recently been published by Watson. This restoration
the writer has reproduced in the present pages, though he has
taken the liberty of making some minor changes, to accord better
with what he believes must have been the position of the shoulder-
blades and the hind legs. And he would also suggest that the tail
in life did not turn down so much at its extremity as depicted by
Watson.

Both Broom and Watson believe that this animal was a power-
ful swimmer, and thoroughly aquatic in habit. To the present
writer, however, this does not seem so evident. He is rather
inclined to believe that the creature was chiefly terrestrial in habit,
living probably in marshy regions, and perhaps seeking its food
in shallow waters and in the mud. Aside from the position of the
nostrils, which it will be observed are rather close to the. eyes,
a position so characteristic of many swimming reptiles and mam-
mals, there is but little indication of aquatic adaptations elsewhere
in the skeleton.

\
WATER REPTILES OF THE PAST AND PRESENT

104

 

Pegipow Apysys ‘uosze Ay Aq pozoysox se ‘snandso4st'T JO U0]SYS—OS “oz

rf yy
CHS

     
ANOMODONTIA 105

The skull is of most extraordinary form. The face is turned
downward, leaving the nostrils high up, in front of the eyes. The
jaws were doubtless covered with a horny shield, like that of the
turtles, having a cutting edge. There is a single pair of elongated
canine teeth, possibly a sexual character. The lower jaws are
heavy and stout, and Watson has said that the animal doubtless
had the ability to open its mouth very widely. The quadrate, the
bone with which the lower jaws articulate, is firmly fixed to the
skull, and there is a single opening on the side of the skull poste-
riorly, a character common to all the Therapsida.

The vertebrae are stout, and they have stout spines. The tail
is remarkably short, stout, and stumpy; it could have been of no
use whatever in the water for propulsion or even for steering. The
front legs are short and stout; the forearm bones are short, sug-
gesting either swimming or digging habits, and the foot is short and
broad. The pelvis or hip bones are massive and were very firmly
connected with the backbone by the aid of six vertebrae, a very
unusual number in reptiles. The hind legs, as figured, show no
indications whatever of aquatic adaptation, unless possibly the
very slight shortening of the shin may be so construed. Watson
believes that the bones of the pelvis, indicate, aside from its strong
union with the backbones, strong swimming powers, but of this
again the present writer is very skeptical. The very strong ischia
and the flatness of the pelvis are both characters found among
American Permian reptiles, which do not show otherwise the
slightest indications of water habits.

If then Lysirosaurus was a powerful swimmer, as has been
maintained, it is very evident that the hind legs must have been
used as the seals or sea-otters use them, to propel and to guide;
but they in nowise resemble the legs of these swimming mammals.
It seems altogether more reasonable to suppose that Lystrosaurus
lived in the marshes, feeding upon vegetable food obtained by aid
of its strong jaws and tusks—if the tusks were possessed by both
sexes; and that the position of the nostrils may be ascribed to
causes like those which brought about their recession in the Phyto-
sauria, and not to strictly aquatic habits. Possibly the animal had
habits somewhat similar to those of the hippopotamus; that it was
106 WATER REPTILES OF THE PAST AND PRESENT

an expert swimmer appears, to the present writer, improbable.
The powerful front legs may be indicative of digging habits; the
animal may have used them as an aid to its powerful jaws and
tusks in uprooting marsh and water plants. However, Lystro-
saurus, whatever may have been its habits, was a curious reptile.
It was about three feet in length, massive in all its structure, and
doubtless of slow and sluggish gait.
CHAPTER VIII
ICHTHYOSAURIA

Early in the eighteenth century a curious work in the Latin
language was published by a famous physician and naturalist—a
professor in the University of Altorf by the name of Scheuchzer—
entitled Querulae Piscium, or “‘Complaints of the Fishes.” The
work was illustrated by many expensively engraved figures of vari-
ous fossil remains, including one of ‘some vertebrae which the
author referred to as “the accursed race destroyed by the flood’’!
The history of the finding of these famous bones is recorded by
Cuvier as follows:

Scheuchzer, while walking one day with his friend Langhans in the vicinity
of Altorf, a village and university of Nuremburg, went to the vicinity of the
gallows to make some researches. Langhans, who had entered the inclosure
of the gallows, found a piece of limestone containing eight dorsal vertebrae,
of a black color and shining. Seized, says Scheuchzer, with a panic terror,
Langhans threw the fragment of limestone beyond the wall of the inclosure,
and Scheuchzer, picking it up, preserved two of the vertebrae which he believed
to be human, and which he figured in his book, Piscium Querulae

About the same time another observer by the name of Baier
discovered other and similar vertebrae in the vicinity of Altorf
which he described and figured as those of a fish; and there was
much earnest contention between Scheuchzer and Baier, as also
between their friends, as to their supposed nature. Scheuchzer’s
figure was often cited as indubitable evidence of the destruction of
mankind by a universal flood, and it was not until nearly a century:
later that Cuvier showed that the bones were really those of a
marine reptile.

It must be recollected, in extenuation of so extraordinary a
blunder on the part of so learned a man as was Scheuchzer, who,
as a physician and professor, one would think ought to have been
able to distinguish between vertebrae so different as are those of an
ichthyosaur and a man, that, during all of the eighteenth century

107
108 WATER REPTILES OF THE PAST AND PRESENT

and well into the nineteenth, the belief was prevalent that all
fossils were the relics of animals and plants that had perished in

 

 

 

Fic. 51.—Restoration of Ichthyosaurus with young, by Charles R. Knight. (By
permission of the American Museum of Natural History.)

the great biblical flood. The science of geology was yet in its
infancy, and there was no known record, other than the biblical
one, of any great inundation of the earth’s surface which might
ICHTHYOSAURIA 109

account for the remains of sea-animals in rocks remote from the
seas. This belief, so long held by even the wisest and most learned
of scholars, so long welcomed by the theologians as proof of the
literal accurracy of the Bible, was one of which Scheuchzer was
quite convinced. His Piscium Querulae was largely a fantastic
discussion of the supposed great world-catastrophe, the Noachian
Deluge, by which the fishes had been destroyed and long imprisoned
in the rocks through no sin of their own.

It was the same author who, in a subsequent work, described and
figured the fossil skeleton of a large salamander which he believed
to be that of a child destroyed in the flood, and which he called
“Homo diluvii testis.” In this specimen, which was discovered in
the Tertiary rocks of Oeningen, and which is still preserved among
the historically as well as scientifically famous fossils of the museum
at Haarlem under the name Andrias Scheuchzeri, Scheuchzer
thought that he detected, not only the skeleton of a child, but even
its brain, liver, muscles, etc.! His engraving of this ‘Witness of
the Flood,” the ‘‘sorrowful skeleton of an old sinner drowned in
the Flood,” as also that of the ichthyosaur vertebrae of Altorf, were
afterward printed in the famous “Copper Bible” as positive proof
of the literal accuracy of the biblical record.

Earlier than the publication of these figures by Baier and
Scheuchzer, at the very close of the seventeenth century, a Welsh
naturalist by the name of Lluyd, in a large and beautifully illus-
trated work, figured—perhaps for the first time—remains of
ichthyosaurs, which he believed to be those of fishes. But
Lluyd accounted for these and all other fossil remains by a
very different theory from that of Scheuchzer and the theologians
—a, theory which at one time had many adherents among scholars.
He believed that the spawn of fishes or the eggs of other
creatures had been carried up from the seas and lands in moist
vapors into the clouds, whence they had descended in rain,
penetrating the earth to give origin to the fossils; in other
words, he believed that all fossils grew in the earth from germs
of the living animals that inhabited the land and seas. Certainly
the old philosophers were hard driven to make facts agree with
theories!
[IO WATER REPTILES OF THE PAST AND PRESENT

Remains of ichthyosaurs, abundant as they were and are in
many deposits in England and Germany, attracted very little
attention from the naturalists of the eighteenth century after the
time of Scheuchzer and Baier, and nothing more was written about
them until 1814, when Sir Everard Home, an English comparative
anatomist, in an extensive series of large and finely illustrated,
though rather discursive, works, described and figured a number
of good specimens. To the animal the remains of which he rather
vaguely and imperfectly described, he gave in 1819 the name
Proteosaurus, in the belief that it was allied to the living Proteus,
a salamander. :

In 1821 the curator of mineralogy of the British Museum—
Koenig by name—after a more critical study of other remains,
reached the conclusion that these animals were intermediate be-
tween the fishes and the reptiles, and gave to them the generic
name Ichthyosaurus, meaning fish-reptile, a name by which the
chief forms have ever since been known. Within the next few
years many specimens of ichthyosaurs were carefully and fully
described by Conybeare, Cuvier, Owen, and others of England,
France, and Germany, making very clear all the more important
details of their skeletal structure. Blaineville, in 1835, thought
that the ichthyosaurs constituted a distinct class of vertebrates
equivalent to all other reptiles, the birds, and the mammals, which
he called Ichthyosauria, the first appearance in literature of the
name by which the order is properly known. Five years later,
however, the famous English anatomist and paleontologist, the late
Sir Richard Owen, united the ichthyosaurs with the plesiosaurs
as a single order of reptiles, to which he gave the name Enalio-
sauria, meaning sea-reptiles, a name which has long been current
. in textbooks and general works on natural history. Moreover,
Owen rather arbitrarily changed Blaineville’s name Ichthyosauria
to Ichthyopterygia, a name which is often, though incorrectly,
used to designate this order of reptiles. These briefly given and
perhaps dry details will make clear how necessary is that rule of
priority upon which naturalists so often insist. When anyone may
change the names of organisms at will there will be no stability
and no uniformity, because there is no one to decide, and the pres-
ICHTHYOSAURIA Int

tige of a great name, like that of Owen, will carry authority till
someone else with greater authority appears. Whether or not the
name Proteosaurus, first given to any member of this order, should
take precedence over the later Ichthyosaurus is still in doubt, since
Home gave no specific name to his species, and the very particular
purists of modern times have decided that a genus is not named
unless the species is also! We moderns sometimes are inclined
to impose very stringent conditions upon the older naturalists;
let us hope that we shall be treated more leniently by the future
naturalists!

It will lead us too far astray to follow in detail the history of
the further discoveries of the ichthyosaurs during the early part of
the nineteenth century.. It may briefly be said, only, that no
other group of extinct backboned animals excited more interest
among scientific men. One incident will suffice. More than sixty
years ago, an interesting deduction as to the living form of the
ichthyosaurs was made by Sir Richard Owen. He observed that
many of the known skeletons, as they were found in their rocky
matrix, had a remarkable dislocation of the vertebrae at a cer-
tain place near the end of the tail, and, although such an append-
age was quite unknown in other reptiles either living or extinct,
concluded that the living animals had a terminal, horizontal,
fleshy fin, very much like that of the whales and sirenians. Sure
enough, discoveries made forty years later disclosed impressions in
the rocks, not only of a large caudal fin, but also of a dorsal fin, as
well as outlines of the flesh-covered paddles. The dislocation of
the vertebrae at the place where the fleshy fin joined the more
slender tail was due to the action of currents of water, or simple
gravitation, upon a thin vertical fin and not, as Owen supposed,
to the twisting of the terminal part as it fell to a horizontal position
after partial decomposition of the soft parts.

About twenty-five years ago, Professor E. Fraas, the present
director of the Stuttgart Museum, described and figured very fully,
not only specimens showing impressions of the fins and paddles,
but also others of well-preserved and very complete skeletons of
different species of ichthyosaurs from the Jurassic deposits of
Wiirtemberg, in which remains of these animals occur in great
II2 WATER REPTILES OF THE PAST AND PRESENT

profusion. His researches, and those of several authors since then,
supplementing and confirming or disproving those of the many
observers made during the preceding seventy years, have finally
determined almost perfectly the complete structure of the more
typical ichthyosaurs, enabling us to infer not a little as to their
habits and distribution in the old Jurassic oceans. Within the
past few years the discoveries.of Professor J. C. Merriam of Cali-
fornia have likewise added greatly to our knowledge of the earlier
ichthyosaurs. It may now truthfully be said that of no group of
extinct reptiles do we have a more complete and satisfactory knowl-
edge than of the ichthyosaurs.

Nevertheless we have yet very much more to learn about the
order Ichthyosauria as a whole—whence they came and how they

 

Fic. 52.—Ichthyosaurus quadricissus. Photograph of specimen in Senckenberg
museum, from Dr. Dreverman.

originated; what their nearest kin were among other reptiles; and
especially, more about the connecting links between them and
terrestrial reptiles. They have, as an order, so isolated a position,
are so widely separated from all other reptiles in structure, that they
have long been a puzzle to paleontologists. Like the whales and
other cetaceans among mammals, we know the ichthyosaurs well
in the plenitude of their power and the fulness of their development,
but have yet only an imperfect knowledge of their earlier history,
and none whatever of their earliest. However, as will be seen
farther on, the recent discoveries by Merriam have shed much light
on some of the stages of their evolution. So nearly perfectly were
all the later ichthyosaurs adapted to their life in the water that it
was believed by nearly all paleontologists until about a score of years
ICHTHYOSAURIA I13

ago that they had descended directly from fishes. But this belief
has been quite abandoned by all, not only because the recent dis-
coveries of the earlier ichthyosaurs have demonstrated a positive
increase in the aquatic adaptations of the later forms, but also

 

Fic. 53.—Bapianodon (Ophthalmosaurus). Skull from the side, from above, and
from below (after Gilmore): ang, angular; bs, basisphenoid; d, dentary; jr, frontal;
£, jugal; Ja, lacrimal; mx, maxilla; na, nasal; oc, occipital condyle; #, palatine; pa,
parietal; pm, premaxilla; po, postorbital; 4s, parasphenoid; pt, pterygoid; pf, pre-
frontal; sa, surangular; s, splenial; sg, squamosal; s¢, supratemporal; g, quadrate;
qj, quadratojugal.

because a double origin of any type of animal life is quite out of
accord with all known facts and principles of paleontology. It is
quite possible for animals, in becoming adapted to peculiar environ-
mental and food conditions, to acquire certain resemblances to
II4 WATER REPTILES OF THE PAST AND PRESENT

other animals, but quite impossible for them to acquire their actual
structure. The ichthyosaurs are true reptiles, and all reptiles
must have had a common origin.

We are sometimes in doubt, however, as to whether characters
resembling those of other animals are really acquired as adaptations
to peculiar environments, that is, parallel, convergent, or homo-
plastic characters, or whether they are due to heredity from remote
ancestors. The reptilian characters of the ichthyosaurs, however,
are so emphatic that they can only be ascribed to heredity. Ichthy-
osaurs are as truly reptilian
as crocodiles or snakes, not-
withstanding their fish-like
form and habits. The ich-
thyosaur ancestors were once
truly land reptiles—of that
we are as sure as we well
can be. Some have thought
that those ancestors were the
primitive Rhynchocephalia,
but most are now convinced
that they were among the

Fic. 54.—Occiput of Baptanodon (Oph- most primitive of reptiles, a
MaRS): pa, pee soc, supraoccip- branch probably from the
ital; sq, squamosal; exoc, exoccipital; op.0, .
paroccipital; sta, stapes; st, supratemporal; cotylosaurs or cotylosaurian
qu, quadrate; gj, quadratojugal; pi, ptery- ancestors. Probably of all

goid; bs, basisphenoid; sag, surangular; ag, the extinct forms that we
angular; art, articular; pra, prearticular. k he P s
(After Gilmore.) now the Proganosauria

come the nearest; indeed it
is not impossible that they may have been the actual forbears of
the ichthyosaurs.

The ichthyosaurs varied in length from two to thirty feet, but
the different species, especially all the later ones, resembled each
other pretty closely in shape; the beak was more slender in some
than in others, and the shapes of the fins and paddles varied not a
little, as we shall see. The jaws were long and slender, provided
with numerous rather small but sharp and recurved teeth, espe-
cially well fitted for the seizure and retention of slippery prey. The

 
ICHTHYOSAURIA IIS

teeth were inserted, not in separate sockets, as are those of the
crocodiles and many other reptiles, but in long, deep grooves, and
were easily lost, indeed so easily lost that one late American form
was originally described as edentulous, and it was not till a number
of years had elapsed that the teeth were found. The nostrils
‘ were small, and situated far back on the sides of the face, near the
eyes. The eyes were very large, not only in proportion to the size
of the skull, but, in the largest species, actually attaining in some,
perhaps, the size of a human head. The eyeball was surrounded
in front by an extraordinarily large and strong ring of ossifications
in the sclerotic membrane, giving not only protection to the eye
under the varying pressure of the water, but also greater control over
vision. The neck was very short, so short, in fact, that no con-
struction was visible in the living animal between the head and
body; it was capable of only slight movement. The trunk was
elongated and relatively slender, sometimes with more than fifty
‘vertebrae in it. The tail also was long and flattened, ending in all
the later species in a large fleshy fin, resembling the caudal fin of
many fishes in shape and doubtless also in function. There was
also a large dorsal fin, supported by hardened or calcified sinews,
in shape like the dorsal fin of most fishes and many cetaceans. This
character is absolutely unique among reptiles, so far as is known,
and was one of the extreme specializations of water life. The hind
‘limbs were smaller, often much smaller than the fore ones, and both
were quite fin-like in life, or rather flipper-like, though not at all
fin-like in structure. The skin was smooth and bare. In brief,
to quote Fraas’s words:

The general aspect of the ichthyosaurs was very dolphin-like. The body
was everywhere naked and probably dark in color. The head was produced
in front into a long, slender snout, and was closely joined to the body posteriorly
without indications of a neck. The body itself was cylindrical, expanded
in front by the large thorax and abdomen, but rapidly diminishing into the
long, slender, and strong tail. Close behind the head were the front paddles,
which in some species were broad and shovel-like, in others elongated and
pointed. The hind paddles were smaller than the front ones, sometimes greatly
reduced in size, their function replaced by that of the very broad tail.

From the foregoing descriptions and the restoration shown
in Fig. 51, we see how very fish-like, or rather dolphin-like, these
116 WATER REPTILES OF THE PAST AND PRESENT

animals were in the external form—so fish-like that the name Ich-
thyosaurus is not misleading, though Koenig gave it in the mistaken
belief that they were really allied to the fishes. When to these
external features certain other fish-like details of the skeleton are
added, we do not wonder that the early observers were so-long in
doubt about them. A more careful examination of the skeleton
will, however, disclose so many truly reptilian characters that their
external appearance and habits lose all significance.

The vertebrae are deeply biconcave and fish-like, it is true, but
a consideration of the reasons therefor will convince us that any
other kind of vertebrae would be more remarkable. At the time
when the ichthyosaurs must have originated, at the time when the
first known ichthyosaurs appeared in geological history indeed, all.
reptiles had biconcave vertebrae, and for the most part at least
deeply biconcave ones. The vertebrae remained fish-like through-
out all their history, perpetuating their type until most other rep-
tiles had developed a firmer one, because such vertebrae were best
adapted for the quick, pliant movements of the spinal.column so
necessary for the well-being of the animals in the water. In the
modern dolphins, animals in shape, size, and habits most wonder-
fully allied to what these old reptiles must have been, the small, flat-
ended vertebrae are widely separated by disks of flexible cartilage.

Not only were their vertebrae fish-like in form, but there are
other characters in the spinal column of a primitive or generalized
nature. As in all aquatic animals, the articulating processes
between the vertebrae are either weak or wanting in the posterior
part of the column. And they were not only small, but were situ-
ated, in many, high up, very remarkably resembling the peculiar
arrangement of the articulations in the dolphins.

There is no sacrum, that is, there were no united vertebrae pos-
teriorly for the attachment and support of the pelvis, as no such
support was needed. In only one other group of aquatic reptiles
was the sacrum lost, though it has wholly disappeared in the ceta-
ceans and sirenians among mammals. The chevron bones of the
tail, usually bony arches on the under side of the tail for the pro-
tection of the blood-vessels, in crawling reptiles, were very imper-
fectly developed in the later forms, though normal in shape in the
early ones. The ribs are numerous, long, and slender, very much
ICHTHYOSAURIA II7

resembling those of the fish-eating dolphins. They usually had,
however, two attachments to the body of the vertebra and none to
the arch, differing in this respect from all other animals.

Of the shoulder bones, the scapula or shoulder-blade, as usual .
among water animals, is short and broad. In the place of a sternum
the coracoids joined each other broadly in the middle, just as they
did in the oldest known land reptiles. And there were clavicles
and an interclavicle. Below the abdomen behind were numerous
slender bones called ventral ribs. The pelvis is very weak, and
was suspended below the spinal column in the fleshy walls of the
abdomen. The hind legs were so small that little support was

 

Jurassic ichthyosaur. (After Gilmore.)

necessary for them, and, because they were not used either for the
support of the body or for propulsion, they did not require a firm
union with the skeleton. Doubtless had the ichthyosaurs con-
tinued to the present time, they would have lost entirely the hind
legs, as have the cetaceans.

It is in the limbs that most extraordinary differences from all
other animals are seen. So great are these differences that it has
been a puzzle to naturalists to understand how they could have
arisen. In no other animals above the fishes, that is, in no other
reptiles, in no amphibians, birds, or mammals, are there ever more
than five fingers or five toes, the number with which air-breathing
animals began. Fingers and toes may be lost and often are lost
in all groups of life, until a single one in each limb may remain, as
in the domestic horse. An increase of fingers and toes, however,
seems to be an impossibility in evolution, and doubtless of real
118 WATER REPTILES OF THE PAST AND PRESENT

fingers and toes it isan equal impossibility. All naturalists are now
agreed that a specialized character can never revert to a generalized
condition, or rather to a generalized structure, that an organ once
functionally lost can never be regained by descendants. A char-
acter once lost is lost foreover; horses of the future can never have
more than one finger or one toe in each limb.

 

Fic. 56.—Front paddle of Oph- Fic. 57.—Front paddle of Mer-
thalmosaurus (after Andrews): h, riamia, a Triassic ichthyosaur.
humerus; 7, radius; w, ulna; p, (After Merriam.) Explanations
pisiform; re, radiale; int, inter- as in Fig. 56.
medium; we, ulnare.

And there was an increase in the ichthyosaurs, in some not
only of the number of digits in each limb, but in all of the number,
of bones in each digit, a character found also in the unrelated
mosasaurs and plesiosaurs. This increase in finger and toe bones,
or hyperphalangy as it is called, is one of the most peculiar of all
the adaptations to water life, changing the feet and hands from
the ordinary walking type to the fish-like swimming type. The
bones beyond the humerus and femur in the ichthyosaurs were so
ICHTHYOSAURIA 119

increased in number and-so changed in form and relations that
they bear little resemblance to the corresponding bones of other
reptiles. They are merely polygonal platelets of bone, articulating
on all sides and fitting closely together, permitting flexibility, but
not much else.

It is now believed that the increase, not only of additional
digits, sometimes to as many as ten in each hand and foot, but of
the finger and toe bones as well, was the result of a sort of vegetative
reproduction. The margins and ends of the flippers were doubtless
hardened by cartilage or fibrous material, and because of the action
of the limbs this cartilagenous material broke up into nodules each
of which took on ossification finally. Among the whales, where
hyperphalangy also occurs, though to a less extent, it has been
thought that the increase in number has been due simply to the
ossification of the parts of each bone normally present, that is, to
the epiphyses, which became separated from the shaft of each bone.
But this explanation will hardly suffice for the fingers and toes of
the plesiosaurs and ichthyosaurs, for there are altogether too many
such ossifications; and besides, the bones in these animals, as in
most reptiles, did not have epiphyses, or terminal separate ossifica-
tions of the bones of the skeleton.

It will be observed from the figures that the arm and thigh
bones of Ichthyosaurus are very much shortened—a striking adapta-
tion to water life, so conspicuously seen in the modern whales
and dolphins as well as in the mosasaurs, thalattosaurs, etc. So
characteristic indeed is this shortening that, were every other bone
of the skeleton of an ichthyosaur unknown save the humerus or
femur, it would be quite certain from these alone that the animal
was thoroughly aquatic in habit.

About sixty years ago a rather aberrant form of ichthyosaur,
now known as Mixosaurus, was discovered in rocks of Triassic age,
that is, of much greater age than any ichthyosaurs previously found,
in which not only the forearm but also the lower leg bones were
longer, resembling more the corresponding bones of land animals.
It was from the examination of specimens in 1887 of these mixo-
saurs that the late Professor Baur became convinced that the
ichthyosaurs were the descendants of land reptiles, and not directly
120 WATER REPTILES OF THE PAST AND PRESENT

of the fishes as they were universally thought to have been at that
time. As Professor Baur very pertinently said, if the ichthyosaurs
were descended from the fishes directly, the earliest forms should
be more nearly like the fishes than the later ones, whereas just the -
opposite was the real fact. The arguments which he gave in sup-
port of his contention were so convincing that they found imme-
diate acceptance among all naturalists. Fortunately within the
past fifteen years many other remains of early ichthyosaurs from
the Triassic rocks of California have been brought to light by Pro-
fessor Merriam, remains which throw a flood of light upon the early,
though not the earliest, history of these strange reptiles. He has
recognized among the forms he has discovered, not only’ new
species, but several new genera, and perhaps new families of ichthyo-
saurs. His studies have demonstrated so well the stages of evolu-
tion between the early ichthyosaurs and the later ones in their
progressive adaptation to water life that it will be of interest to
summarize them here. .

In the early ichthyosaurs locomotion was largely by the aid of
the limbs; in the later ones almost exclusively by the aid of the
caudal fin. In the former the paddles were larger and the bones
longer, more like those of land animals; in the latter they were rela-
tively smaller and shorter, and more fin-like. In the digits of the
early forms the finger and toe bones were more elongated and fewer
in number. The hind limbs were nearly as large as the front ones
in the Triassic, often very much smaller in the later ichthyosaurs;
and the increased number of digits occurs only in the later forms.

In the Triassic ichthyosaurs, all classed in the family Mixo-
sauridae, the pelvis was larger and more firmly connected with the
body than in the later forms.

The skull of the early forms was relatively shorter, as com-
pared with the trunk, the jaws shorter as compared with the head,
the eyes were relatively small, the teeth in some less numerous, and
set in distinct sockets like those of land reptiles; the vertebrae
were relatively longer and less fish-like, and their articulations more
like those of land reptiles.

The distal part of the tail was not bent downward so sharply,
that is, the terminal fin was smaller, or the tail may have been
ICHTHYOSAURIA 121

simply flattened near its end and not really fin-like. The scapula
was longer and less fan-like in shape.

And all these are remarkable evidences of an increased adapta-
tion to water life in the more recent ichthyosaurs over the older
ones. Were someone now so fortunate as to find ichthyosaurs in
late Permian rocks, we should doubtless have the nearly complete
chain between the most highly specialized type of water reptiles
and their terrestrial ancestors.

From the structure of the skeleton alone the early observers
were justified in inferring much concerning the shape and habits
of the living ichthyosaurs. Later discoveries have added so many

 

Fic. 58.—Caudal fin of Ichthyosaurus, after Bauer (left figure); caudal fin of
Mixosaurus, after Wiman (right figure).

definite facts that, at the present time, we know more about their
habits than we do of any other extinct reptiles. In various places
in England and Germany, especially in Wiirtemberg, the remains
of ichthyosaurs are found in extraordinary abundance and perfec-
tion, not only whole skeletons lying in the positions which they had
assumed after the decomposition of their bodies, but also often the
actual remains, carbonized, of the skin, muscles, and ligaments, as
well as delicate impressions of external parts. Many of these
skeletons are obtained from the numerous stone quarries, where
they are a sort of “by-product,” the sums received for them
adding not a little to the income of the quarrymen. So many are
obtained in this and other ways that specimens of ichthyosaurs
122 WATER REPTILES OF THE PAST AND PRESENT

are perhaps more frequently seen in the museums of the world
than those of any other extinct backboned animal. Fairly com-
plete skeletons may now be purchased of dealers in such things for
from fifty to seventy-five dollars. As may be supposed, the best
and most complete collections of these fossil remains are those of
the British Museum in London and the museum in Stuttgart.
From a study of those of the last-mentioned museum Professor
Fraas has learned many interesting facts and reached many inter-
esting conclusions regarding the life-habits of the ichthyosaurs.
In the accompanying figure (Fig. 59) is shown a photographic
reproduction of a very complete specimen, in which not only is
the outline of the whole body shown, but also much of the carbon-
ized remains of the muscles and skin has been detected.

 

Fic. §9.—Ichthyosaurus quadricissus. (From a photograph from B. Hauff,
Paleontologisches Atelier, Holzmaden.)

The attachment of the paddles to the body was broad antero-
posteriorly, proving conclusively that they could not have been
much ‘used in propulsion, either in the water or upon land, since
such use would require a fore-and-aft movement, and a consequent
twisting or rotation of the whole arm or leg, which, because of the
broad attachment, must have been very difficult, if not impossible.

Microscopic examination of the remains of skin preserved dis-
closed an abundance of dark pigment, indicating, Professor Fraas
believes, that the skin was dark colored above. Doubtless, also,
the under side, as in nearly all swimming animals of the present
time, was of a lighter color, because such coloration rendered the
animals much less conspicuous in the water when seen either from
above or below. That the skin was bare is proved by many impres-
ICHTHYOSAURIA 123

sions or molds of it that have been discovered in the rocks, in which
many fine creases are seen, but nothing suggesting scales or bony
plates, save on the front edge of the paddles, where impressions
of overlapping scales have been observed. ‘This is an interesting
fact, bearing witness that their land ancestors had been covered
everywhere with scales, much like those of existing lizards and
other reptiles. Scales or bony plates were not only useless to the
ichthyosaurs in the water, since they could afford no protection,
but would have been detrimental in increasing the resistance in
swimming.

That the ichthyosaurs were predaceous animals is of course
evident from their teeth, adapted for the seizure and retention of
slippery prey, but not for tearing or comminuting. The fossilized
remains of food found between the ribs of some specimens, in the
place where the stomach was, together with fossil excrement,
called coprolites, usually attributed to these animals, prove that
they fed largely upon fishes, squids, belemnites, and probably
other invertebrates. One ichthyosaur specimen preserved in the
Stuttgart Museum has preserved in its stomach contents a mass
composed of the remains of more than two hundred belemnites.

Most interesting of allis the fact that, not very rarely, embryonic
skeletons of ichthyosaurs have been found associated with the
remains of adult animals, in such positions that they must have
been inclosed within the body cavity at the death of the animals.
As many as seven such embryonic skeletons have been observed
with a single specimen. At first it was supposed that these skele-
tons were of small ichthyosaurs which had been swallowed whole
as food, since it is not at all likely that these predaceous reptiles
were discriminative in their choice of food when hungry. It is not
improbable that in some cases this is the true explanation of the
smaller skeletons within the larger ones, but it cannot be true of all,
since wherever the small skeletons are identifiable they have been
found to belong to the same species as the adult, and it would
be absurd to suppose an ichthyosaur bent upon its prey would be
at all likely to select as many as seven young animals, all of the same
size and all of its own species. Furthermore, some of these young
skeletons have been found in such positions as would indicate that
124 WATER REPTILES OF THE PAST AND PRESENT

they were inclosed within their egg-covering at the time of their
death. Some of these embryos measure as much as twenty
inches in length.

Because the ichthyosaurs were born alive, and because so many
of their skeletons are found with their various parts in orderly
relation to each other, it is inferred with much probability that they
were inhabitants, in large part at least, if not exclusively, of the
open and deeper oceans. Had they been oviparous they must
necessarily have laid their eggs upon the beaches, since no reptiles
of the present time lay eggs in the water, and we have no other indi-
cations that the reptiles of the past have ever done so. And such
habits would necessitate the periodical return to land. Had they
been denizens of shallow waters, like the mosasaurs and plesiosaurs
for the most part, their skeletons must surely have been disturbed
by the currents and tides, as also by predaceous fishes, breaking
up or displacing them or carrying away their bones. In shallow
waters, also, the decomposing bodies would have been more liable
to despoliation by the many scavengers of the seas.

The ichthyosaurs must have been quite helpless upon land,
their limbs being of little more use for locomotion than are the fins
of fishes. Breathing air as they did, they were of course not
suffocated when exposed, unless, as is the case with the whales,
the feeble attachment of the ribs prevented the action of the res-
piratory muscles. If accidentally thrown upon the beaches, they
doubtless were able to return to their home element more easily than
the fishes can, by flopping, wriggling, and turning. As we have
seen, the food consisted in part, perhaps the larger part, of small
invertebrates, and because the bones of the lower jaws were closely
united, permitting little or none of that expansion so characteris-
tic of the snakes, all their prey must have been of relatively small
size. In habit the ichthyosaurs were doubtless, like the dolphins
and gavials, inoffensive and harmless, so far as animals of larger
size were concerned. The abundance of their remains often found
in restricted localities, while deposits of like age and character not
far distant may be almost free from them, suggests that in all
probability the ichthyosaurs, or the later ones at least, were more
or less gregarious in habit as are the sea-mammals. They probably
ICHTHYOSAURIA 125

lived in schools, as do the porpoises, each species keeping to its
restricted locality and not wandering far.

The ichthyosaurs began their existence, so far as we now know,
about the middle of Triassic times and continued to near the middle
of Upper Cretaceous, when they disappeared forever from geological
history. As we have seen, however, the earliest forms that we know
were true ichthyosaurs in all respects, though more primitive than
the later ones, indicating a long previous existence of which we yet
have no knowledge. Their remains have been found widely dis-
tributed in Triassic rocks of Europe, Spitsbergen, Australia, and
North America. During the Jurassic period they lived in great
numbers and variety throughout the region that is now Europe.
In North America the only marine rocks of this period that we
know of have yielded numerous remains. These American ichthyo-
saurs were, however, among the most specialized of all ichthyosaurs
—the culmination of their development. They were originally
named Sauranodon in the belief that they were toothless, but in
recent years their teeth, small and numerous, have been discovered.
And the genus seems also to be identical with one previously named
from the Jurassic of Europe called Ophthalmosaurus. The last
known remains of ichthyosaurs have recently been found in the
Benton Cretaceous of Wyoming. Scanty remains of ichthyosaurs
are also known from Australia and New Zealand. Why the
ichthyosaurs should have gone out of existence before the plesio-
saurs and mosasaurs did, one cannot say; possibly their stock had
grown old and feeble.
CHAPTER IX
PROGANOSAURIA

MESOSAURUS

There is some doubt whether those little creatures of Paleozoic
times, to which some years ago the late Professor Baur gave the
ordinal name Proganosauria, are really entitled to so much distinc-
tion among reptiles. The question of their rank has been much
disputed for the past twenty years without any positive conclusion.
Nor were they wholly aquatic in habit, though they did possess many
aquatic adaptations. That they were skilful and fleet swimmers,
and capable of rapid evolutions in the water is quite certain, and,
as the oldest known water reptiles, they are of more than passing
interest.

But two genera and three or four species of the group are known,
and of them, even, our knowledge in some respects is not as com-
plete as one could desire. The first description of any member of
the group was by the late Professor Gervais of Paris in 1867. He
had only the anterior part of a single skeleton, from the Karoo beds
of South Africa, to which he gave the name Mesosaurus, a rather
meaningless term signifying “‘middle” or “‘intermediate”’ saurian.
Nothing more was learned about any form till 1885, when the late
Professor Cope described a specimen from the supposed Carbonifer-
ous of Brazil, which he believed to be closely related to Mesosaurus,
though he had only a very imperfect specimen. He called it
Stereosternum, also a meaningless term, since none of the animals
has a “‘solid sternum,” nor any sternum at all, in fact! A few
years later, in 1888 and 1892, the late Professor Seeley of England
studied a number of specimens of Mesosaurus, adding not a little
to our knowledge of the animals. More recently Dr. Woodward of
England and Professor Osborn of America have given us still further
information concerning them, and within the past few years Dr.
McGregor of Columbia University has figured and described excel-
lent specimens of a new species from Brazil, which he calls Meso-
saurus brasiliensis. Not only were Dr. McGregor’s discoveries of

126
PROGANOSAURIA 127

great interest as settling many doubtful points in their structure,
but they were still more so from the fact that he found his species
so nearly like that from Africa that he placed it in the same genus.

 

 

 

 

 

Fic. 60.—Mesosaurus; life restoration, after McGregor, the posture of hind leg
slightly modified.

Since the proganosaurs were purely fresh-water or terrestrial ani-
mals, one can only wonder how they crossed from Africa to America,
or, what is more probable, how they migrated from America to
128 WATER REPTILES OF THE PAST AND PRESENT

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Fic. 61.—Mesosaurus; restoration of skeleton.

Africa, across the broad Atlantic
Ocean, so long-ago. The geolo-
gists tell us that the Atlantic
and Pacific, in the main, have
always been oceans since the
beginning of terrestrial life upon
the earth. Possibly the tribe of
proganosaurs migrated by the
very circuitous route of Europe
and North America, or Asia and
the Northwest; but that is very
improbable, since nothing what-
ever resembling them has ever
been found in the Northern
Hemisphere, and it is quite
certain that in the many thou-
sands of years it must have
taken them to travel from
southern Africa to South
America many of the reptiles
must have perished on the way
and left their remains in the
rocks. The only conclusion
that seems probable is that
there was a direct land commu-
nication in those olden times
between Africa, or at least
India, and South America across
what is now the Atlantic Ocean.
Of course this route will be
very difficult to prove, since we
can never get to the bottom
of the ocean to hunt for
fossil proganosaurs. Were this
peculiar distribution of the
proganosaurs an isolated
example, one might perhaps
PROGANOSAURIA 129

ascribe our lack of knowledge of any fossil proganosaurs in the
Northern Hemisphere to the meagerness of the fossil records, but
there are many other examples of similar import among other early
animals.

The age of the South American proganosaurs is now believed to
be lower or lowermost Permian, like that of the African Meso-
Saurus; possibly, however, the age first described to Stereosternum
(Carboniferous) may be correct.

The known skeletons are all small, none exceeding a few feet
in length. The skull, as shown in the figure by Dr. McGregor, is
elongate, and its teeth are extraordinarily so, and -very slender.
The external nostrils are situated close to the eyes; and no sclerotic
bones have been discovered. There are small teeth in the bones
of the palate. The neck is elongate, composed of ten or twelve
vertebrae. The trunk also is long and slender, and the tail is not
only long, but also much flattened or compressed. All these
are very characteristic of water life. The limbs, however, show
a much less complete adaptation for swimming—not much more
so in fact‘than do those of the living Crocodilia. The upper arm
and the thigh bones are relatively long, while those of the forearm
and the leg are shorter than among terrestrial reptiles, the first
indication of swimming habits to appear in crawling animals. The
digits are not much elongated, and they have no additional finger
bones, save perhaps in a lately discovered form in Africa, in which
Dr. Broom reports supernumerary bones in the fifth or “‘little”
toe. The fingers and toes have only blunt terminal bones, that is,
they were not distinctly clawed, and they were probably connected
with each other by a membrane, as in a frog’s foot. This webbing
of the feet is probable, not only because of the positions in which
the bones have been found, but also because of the great length of
the “little” toe, which is the longest in the foot, a character quite
abnormal for a land reptile and quite characteristic of certain
aquatic mammals, like the seals and sea-otters. ‘There is a strong
sacrum of two vertebrae, however, the pelvis and hind legs being
connected with the spinal column firmly, clearly proving that, like

tAn additional phalange has also been observed in the fifth toe of a South
American species. -
130 WATER REPTILES OF THE PAST AND PRESENT

the crocodiles, the proganosaurs had by no means lost their land
proclivities. z

Their vertebrae, as would be expected in such old reptiles, are
quite primitive in structure, that is, they are deeply concave in
each end, probably being perforated for the remains of the noto-
chord. The pelvis also is of the old-fashioned type, that is, with-
out an opening or vacuity between the bones below. The shoulder
bones are old fashioned too. The shoulder-blade, especially, shows
a decided adaptation to water life in its short, fan-like shape, very
much like those of the mosasaurs, ichthyosaurs, whales, etc. Just
why swimming animals should have short and broad shoulder-blades
has not yet been explained, but doubtless they afforded better
attachment for those muscles used more especially in swimming.
The ribs are remarkably flat and heavy, and were not very firmly
attached to the vertebrae. Heavy ribs are unusual among free- .
swimming animals, but do occur in the modern sirenians, which
live on the bottoms of shallow bays, etc., feeding upon plants.
We may perhaps infer from this peculiar structure of the ribs that
the proganosaurs lived more on the bottoms of shallow waters, feed-
ing upon such fishes or invertebrates as they could capture, coming
to the surface to breathe from time to time. Possibly they sought
the shores for safety from their enemies, as do the Galapagos liz-
ards, figured on p. 142; and doubtless they laid and hatched their
eggs on land. A character which suggests that the proganosaurs
lived only in the shallow waters is the elongated neck, remind-
ing one of those two other groups of swimming reptiles, the dolicho-
saur lizards and the nothosaurs of the Sauropterygia, the only
known reptiles besides the plesiosaurs having an abnormal number
of neck bones. Still more suggestive of shallow, fresh-water habits
is the absence of eye bones, as in the modern crocodiles.

The long snout, with the long and slender teeth, and the position
of the external nostrils far back near the eyes, together with the
flattened and long tail and the webbed feet, are sufficient proof
of expert swimming habits. The legs still functioned more or less
for the support and propulsion of the body on the land, and they
probably were only of slight service in the water. The alligator
swims sinuously with its front legs collapsed and extended by the
PROGANOSAURIA 131

side of the body; its hind legs are used more as propellers, with
the knee flexed and the feet turned outward and expanded. The
legs of the proganosaurs doubtless were used in the same way, as
shown in the restoration, which has been modified from the original’
of Dr. McGregor in accordance with this probable use of the legs.

There seems to be an incongruity between the posterior nostrils
and the heavy flat ribs, the former suggesting free swimming and
diving habits, the latter shallow-water and bottom habits. Possibly
the position of the nostrils has been the result of the great elonga-
tion of the face in front of the nostrils; and we know that their
posterior position in the phytosaurs (Figs. 95 and 96) has not been
due to swimming habits only. ;

Nothing has been discovered to indicate the nature of the
external covering of the body. Possibly, even probably, the skin
was more or less covered by horny scales or plates, though it may
have been quite bare, as in the salamanders.

To which other reptiles the proganosaurs are nearest related
has long been a subject of dispute, and still is. The more
probable view, however, is that they were a very early branch of
the most primitive stock of reptiles, the Cotylosauria, one that
soon perished, leaving no descendants, unless possibly the ichthyo-
saurs were their progeny. Some writers have thought that they
were the early ancestral stock of the plesiosaurs, and they are often
classified with the Sauropterygia. Still others have believed that
they were an early side-branch of the great group of Rhynchoce-
phalia. And this doubt has been chiefly due to our imperfect knowl-
edge of the bones of the cranium. As has been explained, very
much stress in the classification of reptiles has been laid by students
on the possession of one, two, or no openings on the side of the
skull back.of the eyes. And this part of the skull of the Progano-
sauria has not yet been satisfactorily made out. Dr. McGregor
thought that there are two openings in the temporal region, allying
the group with the Rhynchocephalia. Dr. Huene is more positive
that there is but one, like that of the ichthyosaurs. In this state
of indecision, the proganosaurs may be dignified by giving them an
ordinal position by themselves.
CHAPTER X
PROTOROSAURIA
PROTOROSAURUS

The genus Protorosaurus is of peculiar interest, as one of the
first, if not the first, known fossil reptiles, described by Spener
as long ago as 1710 as a crocodile, from fragmentary remains found
in 1706 in the Permian deposits of Thuringia. Numerous other
skeletons or parts of skeletons attracted the attention of naturalists
of the eighteenth century, but were very imperfectly described.
No name was given to the animal represented by the various speci-
mens until 1840, when Herman von Meyer restudied all the known
material and described it under the name Protorosaurus spenert.
The position of the genus among reptiles always has been and yet
is uncertain, for the reason that the structure of the skull, and
especially the structure of the temporal region, has never been
satisfactorily determined. Seeley, in 1887, described more fully
the original specimen of Spener, now preserved in the museum
of the College of Surgeons of London, and because of certain
peculiarities which it showed proposed for its reception the order
Protorosauria. He thought that he detected an upper temporal
vacuity, like that of lizards, but was very uncertain about the
structure of the lower part of the temporal region. The writer,
who has examined this type specimen, must admit that the struc-
ture of the region here is very doubtful. Under the general assump-
tion, however, that all old reptiles must be related to Sphenodon,
the Protorosauria have generally been classified as a suborder
of the Rhynchocephalia. It is merely another instance of the
proclivity we all have to propose hypotheses, and then, speedily
forgetting that they are hypotheses, to accept them as facts.

Protorosaurus was long supposed to be an aquatic reptile, but
we now know that it was a strictly terrestrial one, probably with
climbing habits; and the genus concerns us only by reason of its
possible relationships to distinctly aquatic reptiles of a later age.

132
PROTOROSAURIA 133

A few years ago the writer described a very slender, lizard-like
reptile about two feet in length from the Permian of Texas under
the name Araeoscelis, so named because of its slender legs. The
structure of both the skull and the skeleton of this reptile is now
quite satisfactorily known, so well known indeed that the accom-
panying restoration (Fig. 62) has little that is conjectural about

 

Fic. 62.—Life restoration of Araeoscelis; about one-fourth life size

it, at least so far as the form is concerned. The skull has a single,
upper temporal opening, quite like that of lizards, but the quadrate
is not loose below. And this is really what we should expect in
the ancestral lizards; and everything else of the skeleton, except
perhaps one character, is what would be expected. That one
character is the elongation of the cervical vertebrae, which are
134 WATER REPTILES OF THE PAST AND PRESENT

 

 

 

 

 

I'1c. 63.—Skeleton of Pleurosaurus. (After Lortet)
PROTOROSAURIA 135

about twice the length of the dorsal vertebrae following them.
The cervical ribs are very slender bones, articulating by a single
head with the centrum only. In these and other characters, so
far as they are known, Araeoscelis seems to agree with Protorosaurus,
and both have very hollow bones.

PLEUROSAURUS

We may for the present be justified in maintaining the order
Protorosauria for. those reptiles having a single, typically upper
temporal opening on each side, with a fixed quadrate, not includ-
ing the ichthyosaurs. It is not improbable, however, that when
more is known of the ancestors of the lizards, the whole group will
find its most natural place among the Squamata. This definition
will include a peculiar aquatic reptile that has been known for
many years, but which has been wrongly classed in the same family
as Sphenodon, on the purely gratuitous assumption that it has two
temporal openings on each side; we now know that it has but one.
This reptile, known scientifically as Pleurosaurus, was described
originally:by H. von Meyer in 1843, but we are indebted to M.
Lortet for a more precise knowledge of the animal, and for the
figure (Fig. 63) which is here given of the skeleton. Not a few
excellent skeletons are preserved in the museums at Lyons and
Munich. The specimen here figured, as actually preserved,
measures about three feet in length; a part of the tail is missing,
which is known from other specimens to have been remarkably long.

The figures show clearly some of the remarkable aquatic
adaptations of the animal, especially the short neck, the very long
and narrow body, and the extraordinarily long and flattened tail.
The head is elongate triangular in shape, resembling very much
that of the mosasaurs; and the external nostrils are likewise situated
remotely from the end of the snout, as in the mosasaurs. The
extremity of the snout has a beak-like projection. The teeth are
much longer, more pointed, and more recurved than is the case
with, most land reptiles, indicating their use for the capture and
retention of slippery, quick-moving prey.

The single-headed ribs are short, proving that the body was
slender and doubtless cylindrical, more like that of a snake. The
136 WATER REPTILES OF THE PAST AND PRESENT

tail was not only enormously elongated, but it was also compressed
into a flat and effective propelling organ in the water. This
flattening of the tail is apparent from the skeleton, with its elongated
chevrons below and spines above, and it is also proved by the for-
tunate preservation of the extremity of the tail of one specimen,
showing not only the impressions of the scales in the matrix, but
also the outlines that the soft parts had in life. To quote from
Lortet, in translation: ‘‘The tail was covered wholly with small
scales, regularly hexagonal in shape, shining and nacreous, larger

 

 

Fic. 64.—Life restoration of Plewrosaurus

on the under side than above. The upper border of the tail was
surmounted by a broad crest, extending to its extremity, and com-
posed of large, oval scales.” The body doubtless was wholly
covered with scales, though it is not probable that the caudal
crest continued along the back.

The limbs begin to show an aquatic adaptation, though not
very pronounced. They are much shorter and smaller than are
those of land-crawling reptiles; and the bones of the second series,
that is, the radius and ulna, tibia and fibula, are relatively short,
the beginning of adaptation to water habits. It is very probable
that the feet were webbed, though the fifth digit, as usual, is shorter
than the fourth. Doubtless on land the creature moved about
PROTOROSAURIA 137

in a serpentine way, for it could not have progressed very rapidly
by the aid of its legs alone. The hind legs are longer than the
front legs, and they were connected firmly with the body by means
of a sacrum. The number of vertebrae in the neck is only five.
The number of dorsal vertebrae is forty-three, a larger number
than is known in any other air-breathing vertebrate with legs.

Upon the whole, these lizard-like, almost snake-like pleuro-
saurians present some very curious adaptations to water life. In
water they were doubtless speedy, swimming in serpentine undula-
tions, with the small legs for the most part folded against the body
and only of occasional use. Doubtless, too, had the pleurosaurs
lived longer in geological history, they would have become quite
snake- or eel-like, just as have some modern salamanders.

In all probability the pleurosaurs lived habitually in ftesh water,
perhaps visiting the shores for refuge, or for the hatching of their
young. That they were not on the way toward a terrestrial
snake-like body is evident from the flattened tail, and especially.
the crest of scales above; the tail was like that of the sea-snakes
of the present time. Pleurosaurus, then, affords the solitary
instance among reptiles of aquatic adaptation by the diminution
of both front and hind extremities and the acquisition of a snake-.
like body and snake-like habits. —
CHAPTER XI
SQUAMATA

The order Squamata, so called because of the dermal covering
of overlapping horny scales, comprises the great majority of living
reptiles. Although the scaly covering is characteristic of nearly
all the members of the order, the most essential differences dis-
tinguishing them from other reptiles are, as usual, found in the
skeleton, and especially in the skull. The quatdrate bone, that to
which the lower jaw is articulated on each side, is not wedged in
immovably between other bones of the skull, as in all other reptiles,
but is, instead, freely articulated with the cranium in such a way
that its lower end moves both backward and forward, as well as
inward and outward. This freedom of movement has in the past
been thought to be due to the loss of a lower temporal arch, a
bony bar connecting the lower end of the quadrate with the hind
end of the upper jaw, which is very characteristic, for instance, of
the Rhynchocephalia. Indeed, because of the many primitive
characters which the lizards possess, it has generally been supposed
that the order was an early branch of the rhynchocephalian stem.
But we are now quite sure that the lizards are as primitive as the
Rhynchocephalia, and that their origin, as an independent branch

_of the reptilian stem, goes quite as far if not farther back—quite
sure that the ancestors of the lizards never had a lower temporal
arcade and two temporal vacuities, but that the looseness of the
quadrate bone has been due to the gradual loss of a bone which
covered the whole side of the skull until only the upper part of
it was left. In other words, the ancestral skull of the Squamata
must have been like that of Araeoscelis, more fully described under
the Protorosauria, a group than which there is perhaps none more
closely allied to the Squamata.

The bones of the roof of the mouth of the Squamata—that is,
of the palate—are narrow and long, and are not closely articulated,

138
SQUAMATA 139

as in most other reptiles; they often bear teeth, a primitive char-
acter. The teeth of all living lizards and snakes are not inserted
in sockets, as are those of the crocodiles, but are co-ossified to the
margins or sides of the jaws or the bones of the palate. But this
is probably not a primitive character; doubtless the teeth of the
early lizards were inserted in sockets like those of most other rep-
tiles. The shoulder bones are absent in many and vestigial in
some others. When present and fully developed, they comprise
the shoulder-blades or scapulae, a single coracoid on each side,
the clavicles, and an interclavicle. The vertebrae, except in some
lizards, are procoelous, that is, with the body concave in front and
convex behind, a peculiar structure that was developed only in
crawling animalst In addition to the usual articulations for the
union of the vertebrae there are also, in some of the lizards
and mosasaurs and all of the snakes, additional ones called the
zygosphene and zygantrum, which will be best understood by
reference to Fig. 12, p. 28. But little less characteristic ‘than
the loose articulation of the lower jaws, so unique in this
order of reptiles, is the manner of attachment of the ribs.
They are always single-headed, articulating only with the body
or lower part of the vertebra. The single-headed ribs of the
plesiosaurs articulate with a projection on each side of the
arch of the vertebra; those of the turtles to the space between
the adjacent vertebrae; nearly all other reptiles have double-
headed ribs, articulating in various ways. This character, it is
seen, though apparently a simple one, immediately distinguishes
a lizard or a snake from all other animals, except the thalattosaurs
and protorosaurs.

There is much difference of opinion among naturalists as to the
proper classification of the different groups of this order of reptiles.
Usually it is divided into four suborders, the Lacertilia or lizards;
the Dolichosauria or long-necked lizards of the past; the Mosa-
sauria, or extinct swimming lizards; and the Serpentes or Ophidia,
the snakes. It matters very little which classification one accepts
so long as it is remembered that the first three groups are closely
related to each other.
140 WATER REPTILES OF THE PAST AND PRESENT

LIZARDS

Popularly a lizard is any four-legged reptile covered with
scales, but such a definition is not strictly correct, since some
lizards are legless and some other four-legged reptiles are covered
with horny scales, notably the tuatera or Sphenodon of New
Zealand, a reptile long classed with lizards, but now known to
belong to quite a different order. Bearing in mind those characters
given as characters of the order, it will be necessary to mention
only those distinguishing the lizards from the snakes.

It is true that the great majority of lizards have four legs, while
the snakes are always functionally legless, but there are some

 

f

 

 

 

 

Fic. 65.—Iguana. (By permission of the New York Zodlogical Society)

lizards, like the glass snakes and the amphisbaenas, or slow lizards,
which are quite legless and there are some snakes which have small
but functionless hind legs. As usual, more important differences
are found in the skull. The brain-case in all snakes is surrounded
on all sides by bone, for the better protection of the brain, with the
head resting quite prone on the ground. The brain of the lizards,
for the most part, is protected on the sides and in front by a simple
membrane. Nearly all lizards have movable eyelids, while snakes
do not; snakes have a single lung, and a protrusible tongue, which
very few lizards possess; and the lower jaws in front are united
in the snakes by a ligament only. Notwithstanding these differ-
ences, the snakes and lizards are closely related animals, and must
SQUAMATA 141

have come from a common ancestry; among all reptiles the known
geological history of the snakes is shortest.

Lizards, on the other hand, have a very high antiquity, begin-
ning, as we now know, at least as long ago as early Triassic times.
They still have many primitive characters in their structure and
are the least advanced type of reptiles now living, with the excep-
tion of the tuatera. Their remains are seldom found in the rocks,
probably because they have always been so strictly terrestrial in
habit, for the most part seldom frequenting even the vicinity of
the water. The true lizards now living number about eighteen
hundred kinds, classified into about twenty families, divided among
four chief groups, of which the chameleons, the amphisbaenas, our
common lizards, and the monitors are representatives.
some ud rather far north in the temperate zone. With the
exception of New Zealand, and the polar and subpolar regions,
lizards are found in all parts of the world. The great majority
live only in high and dry places, though some are denizens of low
and marshy places, a few even not being averse to the water.
They are, for the most part, spry in their movements, some little
ones scarcely six inches in length taxing a vigorous man’s speed
to capture; and many are expert climbers. of cliffs, trees, and
even the ceilings of residences. Some, the remarkable little flying
dragons of Ceylon, have an extraordinary development of the
skin on the sides of the body, supported by the expanded ribs,
forming a sort of parachute whereby the creatures can sail con-
siderable distances through the air. Nearly all are carnivorous,
feeding upon small mammals, birds, other reptiles, frogs, and
insects; a few only are herbivorous, such as the iguanas, which
are often used for human food. Nearly all lizards are oviparous,
laying from two to thirty eggs. In size the great majority are small,
less than a foot in length; but some, such as the monitors and
iguanas, reach a length of from four to six feet, or even more, and
certain extinct monitors of India are known to have attained a
length of thirty feet. They are, for the most part, slender, grace-
ful, prettily marked, and quite inoffensive creatures. A few are
short, flat, or stumpy in shape, such as the so-called horned toad.
142 WATER REPTILES OF THE PAST AND PRESENT

One or two species only, the ‘“‘Gila monsters,” are reputed to be
venomous.

There is but a single species of lizard now living which is in
any true sense aquatic in habit, the well-known sea-lizard of the
Galapagos Islands, scientifically known as Amblyrhynchus cristatus.
It is a large lizard, with a short rounded head, a flat tail, and webbed

 

 

=
eri

<P MEURERX.A.

Fic. 66.—Amblyrhynchus cristatus, the Galapagos sea-lizard. (From Brehm)

feet. Its specific name is derived from the erect fringed crest
along its back and tail. Its habits are best given in Darwin’s

words:

It is extremely common on all the islands throughout the group, and lives
exclusively on the rocky sea-beaches, being never found, at least I never saw
one, even ten yards inshore. It is a hideous looking creature, of a dirty black
color, stupid and sluggish in its movements. The usual length of a full-grown
one is about a yard, but there are some even four feet in length; a large one
weighed twenty pounds. The tails are flattened sideways, and all four feet
are partially webbed. They are occasionally seen some hundred yards from the
SQUAMATA 143

shore swimming about. When in the water this lizard swims with perfect
ease and quickness, by a serpentine movement of the body and flattened tail—
the legs being motionless and closely collapsed to the sides. A seaman on board
sank one, with a heavy weight attached to it, thinking thus to kill it directly;
but when an hour afterward he drew up the line it was quite active. Their
limbs and strong claws are admirably adapted for crawling over the rugged
and fissured masses of lava, which everywhere forms the coast. The nature
of this lizard’s food (seaweed) as well as the structure of the tail and feet, and
the fact of its having been seen voluntarily swimming out at sea, absolutely
proves its aquatic habits; yet there is in this respect one strange anomaly,
namely, that when frightened it will not leave the island. Hence it is easy
to drive these lizards down to any little point overhanging the sea, where
they will sooner allow a person to catch hold of their tails than jump into the
water. They do not seem to have any notion of biting; but when much
frightened they squirt a drop of fluid from each nostril. I threw one several
times as far as I could into a deep pool left by the retreating tide, but it invari-
ably returned by a direct line to the spot where I stood. It swam near the
bottom, with a very graceful and rapid movement, and occasionally aided
itself over the uneven ground with its feet. As soon as it arrived near the edge,
but still being under water, it tried to conceal itself under the tufts of seaweed,
or it entered some crevice. I several times caught the same lizard by driving
it to a point, and, though possessed of such perfect powers of diving and
swimming, nothing could induce it to enter the water; and as often as I threw
it in it returned in the manner described above. Perhaps this singular piece
of apparent stupidity may be accounted for by the circumstance that this
reptile has no enemies whatever on shore, whereas at sea it must often fall a
prey to the numerous sharks.

These lizards are of much interest as indicating one of the ways
in which true land reptiles have become aquatic in their habits.
Tempted by the abundance of food growing in shallow water a
little beyond their reach, the reptiles ventured farther and farther
to obtain it. The tail gradually became a propelling organ,
though the lizard still retained in large measure its land habits
and land feet, because of the dangers from its water enemies. It
is not at all improbable that, in course of time, were these Galapagos
lizards left unmolested, they would become fleeter swimmers by
the development of a terminal caudal fin and paddle-like legs,
thus competing with their aquatic enemies and no longer needing
recourse to the land for protection. They also serve to indicate
that long tailed aquatic reptiles never used their legs to an appre-
ciable extent as organs of propulsion in the water.
144 WATER REPTILES OF THE PAST AND PRESENT

Flat-headed lizards —Among the living lizards there is one group,
called the monitors, which have so many characters peculiar to
themselves that they seem rightfully entitled to an isolated place
among the lizards of the present time. The group includes about
thirty species, all belonging in the one genus Varanus, and all
living in India, Africa, and Australia. In size, some of the species
of Varanus are the largest of all terrestrial lizards known in the
past or present; in other ways also they have reached the maxi-
mum of specialization among lizards. The head is pointed,
broad, and flat, and the body and tail are long. They have nine

 

 

 

 

Fic. 67.—Varanus, Australian monitor lizard. (By permission of the New York
Zodlogical Society.)

vertebrae in the neck, a larger number than is to be found in any
other terrestrial lizard. Unlike other lizards they have a pro-
trusible tongue like that of the snakes. All are carnivorous in
habit, feeding upon small backboned animals, insects, and especially
upon eggs, which they crush between their teeth while holding
them aloft. Most species live wholly upon the land, and some
are arboreal. Others, especially those of the Nile, live about
water and are excellent swimmers. The terrestrial species have a
round tail and small external nostrils, but the water species have
the tail much flattened, and the nostrils have large cavities,
which, when closed under water, are said to serve as reservoirs of
SQUAMATA 145

air for respiration. Of one of these swimming species Annandale
writes:

Varanus salvator is common in Lower Siam where it is equally at home on
land, in water, and among the branches of trees. The eggs are laid in hollow
tree trunks. When in the water the lizard swims beneath the surface, the legs

being closely applied to the sides, and the tail functioning both as oar and
rudder.

These lizards take to the water to escape from their land
enemies and not for food, a habit also known among certain other
lizards, and one precisely the reverse of that of the Galapagos
lizards. It would seem very probable that animals of such carniv-
.orous habits as are the monitors might easily learn to capture
water animals for food and thus eventually become aquatic in
habit. This inclination toward, and partial adaptation to, water
habits in the monitors is of much interest because in all probability
the instinct is one of long inheritance from those remote ancestors
which gave origin to the truly aquatic members of the order.
Though the known geological history of the monitors does not
extend far back, they are so intimately. allied in their anatomical
structure to the aquatic and semiaquatic lizards of Cretaceous
times that there could seem to be no doubt of the common ancestry.

Dolichosaurs.—About fifty years ago Professor Owen, the famous
English paleontologist, described a peculiar semiaquatic lizard
.from the Cretaceous rocks of England to which he gave the name
Dolichosaurus, in allusion to. the slender form of the body. Just
what relations these slender lizards have to modern lizards has long
been a problem; some have thought that they were their pro-
genitors, but there are very good reasons for doubting this. No
modern lizards, save the monitors, have more than eight vertebrae
in the neck, while these dolichosaurs had as many as seventeen, a
remarkable specialization for aquatic life that could hardly have
been lost by their descendants. For this reason the dolichosaurs
have usually been considered as representing a distinct suborder.
‘But they have many resemblances otherwise to the monitors.
They were semiaquatic in habit, and. never more than six feet
in length. They are yet imperfectly known, and no restoration
of any form has hitherto been attempted. Their peculiar interest
146 WATER REPTILES OF THE PAST AND PRESENT

lies in the elongation of the neck, quite like that of the wholly
unrelated nothosaurs and proganosaurs, which have been described
in the foregoing pages. Doubtless similar habits in each had like
results, but just what these habits were in the slender lizards we
do not yet know.

Aigialosaurs.—Within recent years a number of other lizards
have been made known from the Lower Cretaceous rocks of Dal-
matia which present most remarkable intermediate characters
between the monitors, dolichosaurs, and the mosasaurs, the famous
sea-lizards of Upper Cretaceous age. Some of these lizards had
twelve or thirteen vertebrae in the neck, while others had but
seven—an unusually short neck characteristic of the mosasaurs.
These latter kinds, belonging to two or three genera, are included
in a distinct group. They were long and slender, the head
long and pointed. The teeth, conical and sharp, were attached
in shallow pits, quite as in the mosasaurs. The lower jaws had a
hinge just back of the teeth, as in the mosasaurs, of which the only
trace in modern lizards is found among the monitors. Still more
remarkable, though perhaps not so easily appreciated, is the shape
of the quadrate bone, with a broad flaring rim for the ear cavity,
quite unlike that of land lizards, but quite like that of the mosa-
saurs. In fact, the very peculiar skull is almost identical with that
of the true sea-lizards. The body and tail also resemble those of
the mosasaurs more than those of the monitors, but there is a
firm attachment of the pelvis to the backbone, and the legs are
long and lizard-like, though not as long as those of land lizards.
The feet were webbed in life, and the toes have no claws, conclu-
sively demonstrating their water habits. The vertebrae indeed
have the same peculiar articulations, called zygosphenes, as in
most of the mosasaurs. The largest aigialosaurs were about six
feet in length, that is, of about the size of the smallest known
mosasaurs.

We have then in the aigialosaurs nearly every known inter-
mediate character that we could wish for in a connecting link
between the mosasaurs and the monitors, lizards that were equally
at home on land or in the water, and there can be scarcely a doubt
that they were either the direct ancestors or closely akin to the
SQUAMATA 147

direct ancestors of the strictly marine mosasaurs; and scarcely
a doubt that they were the descendants of the actual forbears

<f

 

 

 

 

 

Fic. 68.—Clidastes, an American mosasaur. Life restoration

of the modern monitors, which, as we have seen, have acquired
partial aquatic habits in escaping from their enemies. The
148 WATER REPTILES OF THE PAST AND PRESENT

dolichosaurs we can now understand were a side branch from these
semiaquatic aigialosaurs which, specializing in another direction,
quickly came to grief, perhaps in competition with their more
agile and skilful short-necked kin.

Taking all these facts into consideration it seems best to unite
the monitors, dolichosaurs, and aigialosaurs into one group of
the Lacertilia, the Platynota, intermediate in place between the
true land lizards and the truly aquatic mosasaurs.

MOSASAURS

At St. Pietersberg, a small mountain in the vicinity of Maes-.
tricht, Holland, there are immense subterranean stone quarries,
which have been worked for more than a thousand years. The
stone quarried from them is a sandy limestone of Upper Cretaceous
age containing many well-preserved remains of extinct animals
that have long been sought by collectors of fossils. In 1776 Major
Drouin—an officer of a near-by garrison, one of much military
importance in those days—secured from one of these quarries
some bones of an extinct reptile, which, though of interest, afforded
but little information concerning the structure and affinities of the
animal to which they had once belonged. In 1780 a very perfect
skull, in excellent preservation, of the same kind of an animal was
obtained from the same quarry by Dr. Hofmann, an army surgeon
of the same garrison, whose interest in such things had been incited
by Major Drouin’s collections. This specimen, so renowned in
science, has had a remarkable and eventful human history, in
part related by St. Faujas de Fond, a French commissary of the
‘Army of the North,” and one of the participants:

In one of the great galleries or subterranean quarries in which the Cre-
taceous stone of St. Pieter’s Mount is worked, about five hundred paces from
the entrance, and ninety feet below the surface, the quarrymen exposed part
of the skull of a large animal in a block of stone which they were engaged in
quarrying. On discovering it they suspended their work and went to inform
Dr. Hofmann, surgeon to the forces at Maestricht, who for some years had
been collecting the fossils from the quarry, remunerating the workmen liber-
ally for the discovery and preservation of them. Dr. Hofmann, arriving at the

spot, saw with extreme pleasure the indication of a magnificent specimen; he
directed the operations of the men, so that they worked out the block without
SQUAMATA 149

injury to the fossil, and he then, by degrees, cleared away the yielding matrix
and exposed the extraordinary jaws and teeth, which have since been the sub-
ject of so many drawings, descriptions, and discussions. This fine specimen
which Dr. Hofmann had transported with so much satisfaction to his collection,
soon became, however, a source of much chagrin to him. Dr. Goddin, one of
the canons of Maestricht, who owned the surface of the soil beneath which was
the quarry whence the fossil was obtained, when the fame of the fossil reached
his ears, pleaded certain feudal rights in support of his claim to it. Hofmann
resisted and the canon went to law. The whole chapter supported their rever-
end brother, and the decree ultimately went against the poor surgeon, who
lost both the specimen and his money, for he was made to pay the costs of the
action. The canon, leaving all remorse to the judges who pronounced the
iniquitous sentence, became the happy and contented possessor of this unique
example of its kind. [Translation by Leidy.]

But the canon was ultimately despoiled of his ill-gotten treasure.
At the siege of Maestricht in 1795, the famous skull to which Hof-
mann had devoted so much anxious thought and labor, fell into
the hands of the French and was carried off as one of the spoils
of war. So widely celebrated had the specimen become during
the fifteen years which had elapsed since its discovery, through
the writings of several noted scientific men, that the French general
commanded his artillerists to spare the house in which it was known
to be. The canon, however, shrewdly suspecting that such an
unexpected and extraordinary mark of favor was not for his own
sake but rather for the sake of the famous fossil, had it removed
and carefully hidden in a house in the city. After the capitula-
tion of Maestricht the eagerly sought-for fossil was not to be found,
and the offer of a reward of six hundred bottles of wine, so the
story goes, was made for its recovery. So tempting was the offer
that, ere long, it was brought in triumph to the house of St. Faujas
de Fond, by a half-dozen grenadiers, whence it was later trans-
ferred to Paris, where it now is.

We may well sympathize with Dr. Hofmann in the loss of his
cherished specimen, since, had it not been for his zeal, money, and
labor, it would never have escaped the usual fate of such things—
complete destruction. But we must remember that St. Faujas
de Fond, the recorder of this history, was a Frenchman, and some-
what interested in robbing the reverend canon of it; possibly there
is another side of the story which has never been told.
I50 WATER REPTILES OF THE PAST AND PRESENT

After peace was declared, one has regretfully to add that the
canon, not Dr. Hofmann, was reimbursed for it, or so it is said.
Cuvier rather naively says that it was ceded to the Garden of
Plants of Paris, perhaps in the way that many other things are
ceded to the conqueror in time of war. The specimen is really
a good one, even when compared with many found in recent years,
and there is little wonder that the cupidity of St. Fond was incited
by it. Casts of it are now or have been in nearly every noted
museum of the world, and pictures of it illustrated nearly every
textbook of geology published during the first three-quarters of the
past century. It had been the subject of considerable contro-
versy even before it came into the hands of Cuvier. Peter Camper
figured and described the skull as that of a whale or ‘breathing
fish’’; while St. Fond himself later called it a crocodile. Crocodile
or alligator skeletons were rare in those days, and St. Fond
made a special trip to the British Museum to study one. But it
was really Adrian Camper, a son of Peter Camper, who deserves
the credit, so often wrongly ascribed to Cuvier, for the recognition ~
of the true nature of the fossil. He insisted that the animal was
a lizard allied to the living monitors, an opinion which it will
be seen has finally been proved to be correct within very recent
years.

In 1808 this famous skull, and all other known remains of a
similar nature, came under the observation of Cuvier, the renowned
French naturalist and paleontologist, who confirmed the views of
Adrian Camper. He fully described and figured all the known
parts of the skeleton that had later come to light, calling the animal
the great lizard of the Meuse, the river near which Hofmann’s
specimen was found. Conybeare, a well-known paleontologist
of England, some years later formally christened it Mosasaurus,
a transliteration of Cuvier’s phrase, from the Latin Mosa, for
Meuse, and saurus, a lizard. For more than half a century Cuvier’s
figure of the skull of the original specimen appeared in works
on geology over the name Mosasaurus hofmanni, or Mosasaurus
camperi. One could wish that the former name for the species
might prevail, in recognition of the zealous doctor who was so
shabbily treated in his possession of the specimen.
SQUAMATA

For some years the few specimens discovered
by Drouin and Hofmann were all that were
known of the mosasaurs. A few others of
related forms were discovered in England, and
some were reported from New Jersey by early
explorers, but there was little published about
the mosasaurs till 1843, when Dr. August Gold-
fuss, a noted German paleontologist, described
and beautifully figured an excellent specimen
from the United States. This specimen also
had a rather eventful history. It was dis-
covered early in the fourth decade by Major
O’Fallen, an Indian agent, near the Great Bend
of the Missouri River, whence it was trans-
ported by him to. St. Louis and placed in his
garden asa curiosity. It happened that Prince
Maximilian of Wied, the famous naturalist, in
his travels through the United States, saw the
‘specimen and secured it, taking it to Germany
on his return. He presented it to the Museum
of Haarlem where Goldfuss saw and described
it. Rather oddly, this specimen was of a
species closely allied to the original one of
Maestricht, a species which has since only
rarely been found. It was called Mosasaurus
maximiliani by Goldfuss, though some time
previously, it has since been found, some frag-
ments of the same species were described by
Harlan, an American author, under the name
Ichthyosaurus ‘missouriensis. Goldfuss’ paper
was strangely overlooked by subsequent
writers, and it was not till the discovery of
numerous remains of mosasaurs by Leidy,
Cope, and Marsh in the chalk of western
Kansas, nearly thirty years later, that much
was added to the world’s knowledge of these
strange reptiles.

 

 

151

Fic. 69.—Skeleton of Platecarpus as mounted in the Paleontological Exhibit, Walker Geological Museum, University of Chicago
152 WATER REPTILES OF THE PAST AND PRESENT

Perhaps nowhere in the world are the fossil remains of marine
animals more abundantly and better preserved than in these
famous chalk deposits: of Kansas. The exposures are of great
extent—hundreds of square miles—and the fossil treasures they
contain seem inexhaustible. Long-continued explorations by col-
lectors have brought’ to light thousands of specimens of these
swimming lizards, some of them of extraordinary completeness
and perfect preservation, so complete and so perfect that there is
scarcely anything concerning the mosasaurs which one might hope:
to learn from their fossil remains that has not been yielded up by
these many specimens. The complete structure and relations of
all parts of the skeleton, impressions of the bodies made in the soft -
sediments before decomposition had occurred, the character of
their food, the nature of the skin covering, and even some of the
color markings of the living animals have all been determined with °
certainty. Not only from Kansas, but also from many other
parts of the world, have remains of these animals been discovered,
until now it may truthfully be said that no other group of extinct
reptiles is better represented by known fossil remains than the
mosasaurs. From England, Belgium, Russia, and France in
Europe; from New Jersey, Georgia, Alabama, Mississippi, Texas,
New Mexico, Colorado, Kansas, Nebraska, the Dakotas, Wyo-
ming, and other places in the United States; from New Zealand
and South America they have. been obtained in greater or less
abundance and perfection.

Their geological history is relatively brief, notwithstanding
their wide distribution over the earth in such great numbers and
diversity. The earliest are known from near the beginning of the
Upper Cretaceous of New Zealand, whence it is believed by some
that they migrated to other parts of the world, appearing in
North America some time later. They reached their culmination in
size, numbers, and variety very soon, and then disappeared forever
before the close of Cretaceous time. The largest complete speci-
men of a mosasaur known measures a little more than thirty feet
in length, but incomplete skeletons of others indicate a maximum
length of about forty feet. The skulls of the largest species are
about five feet long. The smallest known adult skeletons are
SQUAMATA 153

scarcely eight feet in length. There are now known at the present
time seven or eight genera of three distinct types, all belonging
to one family, the Mosasauridae, including about twenty-five
known species. While a few of the genera are widely distributed
over the earth, the species are all of restricted range, indicating,
perhaps, non-migratory habits.

The adaptation of the mosasaurs to an aquatic life was very
complete, though perhaps not so complete as was that of the
ichthyosaurs. The skull is flattened, narrow, and more or less
elongate, but large in proportion to the re-
mainder of the skeleton—nearly one-sixth of
the entire length; that relative size doubtless
is indicative of very predaceous and pugna-
cious habits. The teeth in the typical forms
are numerous, strong, and sharp, conical in
shape, and recurved. Not only are there
numerous teeth in both the upper and lower
jaws, but there are also two rows of strong
teeth implanted in the back part of the
palate, upon bones called pterygoids, the use
of which will be understood later. The teeth
were inserted on large, tumid, bony bases,
rather loosely attached in shallow pits or
alveoli, unlike the teeth of all modern lizards.
Such a mode of attachment of the teeth

 

Fic. 70.—Tooth of
Tylosaurus, two-thirds
doubtless had some relation to the habits of natural size.

the animals concerning which we are not

quite clear. They were easily dislodged, and, in consequence, of
very unequal size, some full grown, some small, and others just
appearing above the surface of the gums in the living animals.
The frequent loss of teeth and their constant and easy replace-
ment by new ones is a peculiarity of predaceous reptiles, thereby
insuring their best functional use.

The external nostrils, of large size, were situated at a consider-
able distance back of the end of the snout, but not nearly so far
back or so near the eyes as were the nostrils of the ichthyosaurs,
plesiosaurs, and phytosaurs. Their size and position suggest a
154 WATER REPTILES OF THE PAST AND PRESENT

use like that of the modern aquatic monitors, as mentioned on a
preceding page. The eyes were of moderate size, those of the less
purely aquatic forms being directed more laterally than those of
species of more distinctly diving habits. They were protected
by a stout ring of bony plates, as were the eyes of all truly aquatic
reptiles of the past. The ears, also, in most if not all mosasaurs,
had a thick cartilaginous ear-drum in place of a simple membrane,
evidently, as Dollo has shown, for better protection under undue
pressure of the water in deep diving.

As in all other lizards, the bones with which the lower jaws
articulate, the quadrates, were loosely attached at the upper end,
permitting great freedom of movement in all directions, more even
than the land lizards have. The lower jaws were long and powerful,
armed with a single row of teeth on each side, from sixteen to

 

Fic. 71.—Clidastes, inner side of right mandible: ang, angular; art, articular;
cor, coronoid; fa, prearticular; swr, surangular.

' eighteen in number. Just back of the teeth, a little beyond the
middle, each mandible has a remarkable joint, quite unknown in
land lizards, though a trace of it is found in the monitors, per-
mitting much movement between the front and back parts, both
laterally and vertically, though chiefly in the former direction.
Furthermore, as in land snakes but not as in land lizards, the
front ends of the two sides of the jaws were somewhat loosely
attached to each other by ligaments. This looseness of the two
sides of the jaws, not only in front but also behind, together with
the joint in each, was of the greatest use in swallowing prey, as
will be explained farther on.

As in most other aquatic reptiles, the neck was short and strong,
the vertebrae being less in number than in most other lizards.
The trunk was long and slender, more especially so in the surface- ~
swimming kinds, with from twenty-two to thirty-four vertebrae.
SQUAMATA 155

The tail was long, no longer than the tail of some land lizards,
but more powerful, and broader and flatter. It was expanded or

 

Fic. 72.—Skulls of mosasaurs. Upper figure, Clidastes, from the side; middle
figure, Platecarpus, from below; lower figure, Tylosaurus, from above: an, angular;
bs, basisphenoid; c¢, coronoid; ep, epipterygoid; fr, frontal; 7, jugal; , lacrimal; m,
maxilla; 2a, nasal; oc, occipital condyle; pa, parietal, palatine; pm, premaxilla;
pf, prefrontal; pt, pterygoid; po, postorbital; g, quadrate; sp, splenial; sg, squa-~
mosal; i, transverse; ¥, vomer.

dilated more or less toward the free end, that is, with the beginning
of a terminal caudal fin, such as the more specialized ichthyosaurs
and crocodiles possessed. The vertebrae were procoelous, that is,
156 WATER REPTILES OF THE PAST AND PRESENT

concave in front and convex behind, like those of most modern
lizards and all modern snakes and crocodiles, but quite unlike the
biconcave vertebrae of all other aquatic reptiles. This kind of
articulation of the backbones gave greater firmness and strength
to the spinal column, but decreased the flexibility, and its posses-
sion by these animals was doubtless due to their descent from
land lizards which had already acquired it. The loss of flexibility,
however, was partly compensated by the loss of the additional
articulating surfaces of the tail.

As in all other aquatic reptiles, it is in the limbs that the most
striking characteristics of these water lizards or ‘‘sea-serpents”
are found. The legs were so completely adapted to an aquatic

: mode of living that the ani-
mals must have been practi-
cally helpless upon land, able
perhaps to move about in a
, serpentine way when acci-

| dentally stranded upon the
7 beaches, but probably never

Le seeking the land voluntarily.
Fic. 73.—Platecarpus; occipital view of The front limbs, like those of
skull: bo, basioccipital; co, exoccipital; *f, all other swimming animals
postfrontal; st, stapes; pt, pterygoid; q, having a powerful propelling
quadrate.

: tail, were larger than the
hind ones, though not very much so. The bones of the first
two segments, that is, the arm, forearm, and thigh and leg
‘bones, were all short and broad, resembling those of the ichthyo-
saurs more than those of any other reptiles, save perhaps the
thalattosaurs, discussed below. The articular surfaces of all the
the limb bones, as in other aquatic animals, were restricted in extent,
indicating limited motion between the joints, though doubtless
having great flexibility. In the most specialized types, such as
Tylosaurus, the wrist and ankle bones were almost wholly carti-
laginous, just as they are in the water salamanders, and in whales
and porpoises. This tendency of the ends of long bones, the wrists
and ankles as well as other bones of the skeleton, to become more
cartilaginous, or less well ossified, in animals purely aquatic in

 
SQUAMATA 157

habit is a marked one. So much is this the case that paleontolo-
gists always suspect water habits in reptiles showing it, even though
but few parts of the skeleton are known.

Increase in the number of bones of the digits is a more or less
conspicuous characteristic of all mosasaurs. In those forms in

 

Fic. 74.—Clidastes; left front paddle: Fic. 75.—T ylosaurus; left front paddle:
c, coracoid; #, humerus; 7, radius; sc, c, coracoid; sc, scapula; #, humerus; 7,
scapula; #, ulna. radius; , ulna.

which the wrists and ankle bones had become cartilaginous in great
part, as many as eleven phalanges have been observed in the longest
toes, though in other forms, those with more completely ossified
wrists and ankles, only two or three additional bones have been
developed in the longest fingers and toes by aquatic habits. The
158 WATER REPTILES OF THE PAST AND PRESENT

pliability and flexibility of the fingers and toes were certainly very
great, but they could not possibly have been flexed or bent so
as to grasp or seize anything; and of course all vestiges of claws
had disappeared. Many specimens have been found with all the
bones of the limbs, that is, the “paddle bones,” in the positions they
occupied when the animals
died. Figures of three such
specimens, made from photo-
graphs or careful drawings by
the writer, are shown here-
with (Figs. 74-76). In several
such specimens very clear
impressions of the smooth
membranes between the
fingers have been observed,
and in. one specimen pre-
served in the collections of
the University of Kansas the
outline of the fleshy parts
connecting the paddle with
the body has been preserved.

It will be seen by com-
parison of the figures of the
mosasaur paddles with those
of the ichthyosaurs and ple-
siosaurs that there was a wide
difference in their structure,
though all have the charac-
teristic shortening of the limb
bones and increase in the
numbers of the finger and
toebones, that is hyperphalangy. It is probable that these differ-
ences mean a more powerful and varied use of the limbs in the
mosasaurs. It is certain that the mosasaurs were much more pre-
daceous and pugnacious in their habits than were any other truly
aquatic backboned air-breathing animals of the past or present.
They were the “land sharks” of the ancient seas, and probably

 

Fic. 76.—Platecar pus; right front paddle:
h, humerus; r, radius; , ulna.
SQUAMATA 159

the only ones among water reptiles that would be dangerous and
offensive to man, were they all living today.

For a long time it was thought that the mosasaurs had no
breast bone, and that, in consequence, the front part of the thorax
was expansible. Under this assumption the mosasaurs would have
been much more snake-like in habit than they really were. The
loose construction of the jaws doubtless permitted the swallowing
of prey of considerable size, and the inference was that they habitu-
ally preyed upon animals of large size. A snake will often swallow
a frog of larger diameter than its own body, the flexible jaws and
loosely connected ribs permitting it to pass to the abdominal
cavity. But the unyielding ring formed by the anterior ribs con-
nected with the breast bone in the mosasaurs, as in other lizards,
conclusively proves that large animals could not have been swal-

 

Fic. 77.—Platecarpus; pelvis, from below: #, pubis; i/, ilium; is, ischium

lowed whole by the mosasaurs. In several instances the fossilized
stomach contents, composed chiefly or wholly of fishes, have been
found between the ribs of mosasaurs, and in none were the fishes
more than two or three feet in length, though the reptiles were
from sixteen to twenty feet long. Possibly the largest mosasaurs
those thirty or thirty-five feet in length, might have captured and
swallowed fishes six or seven feet long, but in all probability their
usual prey was of smaller relative size.

The very loose construction of the pelvic bones, those to which
the hind legs are articulated, is an evidence of more complete
adaptation to water life than was or is the case with any other
water air-breathers except the ichthyosaurs and cetaceans. The
sacrum had entirely lost its function as a support to the pelvis
and had disappeared, that is, the vertebrae composing it had become
160 WATER REPTILES OF THE PAST AND PRESENT

quite like the adjacent ones, by the loss of the ribs connecting them
with the ilium. The small pelvis was suspended loosely in the
walls of the abdomen, or at the most was feebly connected with
a single vertebra by ligaments. It was entirely useless as a support
for the legs. The mosasaurs could not possibly have raised their
bodies from the ground while on land. It is well known that the
land lizards and the crocodiles raise their bodies free from the ground
while running or walking; none drags its body over the surface.
In several instances complete or nearly complete skeletons of
mosasaurs have been discovered with the different bones nearly
all in the positions and relations they had after the decomposition
of the flesh, together with the carbonized remains of the skin and

 

Fic. 78.—Photograph of carbonized remains of scales of Tylosaurus, natural size

impressions of the investing scales and membranes. The nature
of the body covering is therefore known with certainty from nearly
all parts of the body. The body everywhere, save on the mem-.
brane between the fingers and toes, and perhaps on the top of the
skull, was covered with small overlapping scales, very much like
those of the monitors. These scales, however, were small and
smooth in comparison with the size of the animals, those of a
mosasaur twenty feet in length being almost precisely the size
of those of a monitor six feet long. The top of the skull seems to
have been covered with horny plates, as in most lizards. In one
instance parallel dark bars, obliquely placed, and of narrow width,
formed by carbonized pigment, were observed by the writer. As
has been stated, in some instances fish bones and fish scales have
SQUAMATA 161

been observed among the fossilized stomach contents, and it is
quite certain that the food of these creatures must have been com-
posed chiefly of fishes, though of course it is not improbable that
other small vertebrates, birds, pterodactyls, the young of plesiosaurs,
and possibly small mammals, may occasionally have formed a
part of their diet. That the mosasaurs were very pugnacious
in life is conclusively proved by the many mutilations of their
bones that have been observed, mutilations received during life
and partly or wholly healed at the time of death. Bones of all
vertebrates are repaired after injury by the growth of more or less
spongy osseous material about the injured part, forming a sort
of natural splint. This material is more or less entirely removed
by absorption when it is no longer required for the support of the
broken ends. Many such injured bones of the mosasaurs have
been found; sometimes the bones of the hands and feet have grown
together, and not infrequently the vertebrae have been found
united by these osseous splints; occasionally even the skull itself,
especially the jaws, attest extensive ante-mortem injuries. In a
single instance the writer has observed the loss of a part of the tail,
where it probably had been bitten off. It may be mentioned, how-
ever, that the bones of the tail had no such ‘‘breaking points” in
the mosasaurs as have those of many land lizards, whereby a part
or all may be lost as a result of even a trivial injury, and then
regrown. Such a condition in an organ relied upon entirely for
propulsion would have been immediately fatal to the existence of
the mosasaurs. The large jaws and teeth are in themselves suffi-
cient evidence of the fiercely carnivorous propensities of the mosa-
saurs. The constant renewal of the sharply pointed teeth, thereby
preventing deterioration by use or accident, preserved, even in the
oldest-animals, the effectiveness of the youthful structure.

We may now understand how the mosasaurs seized and swal-
lowed their prey. Living constantly in the water, away from all
firm objects, with small, short limbs quite incapable of holding
struggling prey, and the body not sufficiently serpentine to hold
it in its folds after the manner of snakes, the mosasaurs would have
found it difficult or impossible to swallow fishes of even moderate
size, were their jaws of the same construction as are those of the
162 WATER REPTILES OF THE PAST AND PRESENT

land lizards. If they preyed upon small animals only, or if they
tore their prey to pieces after the manner of the alligators, there
would have'been no especial difficulty in deglutition. But it is
certain that the animals which the mosdsaurs devoured were not
always small, and they must have been swallowed whole, since their
teeth were not adapted, like those of the alligators and true croco-
diles, for the rending of bodies. One who has watched a snake swal-
low a frog or another snake will appreciate the difficulties against
which the mosasaurs contended in swallowing fishes a fifth or a
sixth of the length of their own bodies. The ordinary snake, no
matter where or how it seizes its prey, invariably swallows it
head first. Its mandibles are even more loosely united in front
than were those of the mosasaurs, and while there is no joint in
the snake’s mandibles such as there is in the mosasaurs’, the loose
union of the various bones of the mandibles serves the same purpose.
The frog or lizard, while firmly held by the slender teeth, is slowly
moved sideways by the alternate lateral action of the jaws till
the head is reached. Many non-poisonous snakes, if they find it
impracticable or impossible to reverse the position of their prey
in this way, wrap the folds of their body about it, holding it firmly
while they release their mouth-hold and seize it by the head.
An amusing instance of these habits came under the observation
of the writer not long ago, in Texas. A large ‘blue racer” (Bas-
canion), six feet four inches in length, caught an unusually large
bullfrog by one hind leg, but in almost less time than it takes to
relate, the head of the frog had entered the snake’s gullet and the
mouth was closed over it, notwithstanding the vigorous muscular
and vocal protests on the part of the frog. Wishing to secure
the skull of the snake for his collection, the writer seized an ax
standing conveniently by and cut the snake cleanly in two. The
peristaltic action of the deglutitional muscles carried the frog
slowly on about two feet farther to the ax-made orifice, from
which it emerged, and, after a few croakings against such unkind
usage, calmly hopped off into the near-by pool of water! Many
poisonous snakes release their prey after killing it; other snakes
may force their prey down the throat by pressing it against
the ground.
SQUAMATA 163

Even small fishes could not possibly have been swallowed by
the mosasaurs in any other way than head first, since the back-
wardly projecting, and often long, spines would have rendered
any other procedure impossible. Even after the head had entered
the gullet, deglutition could have been effectively completed only
by the aid of some mechanism whereby the fish could have been
pulled or pushed back into the constricting fauces. .The strong
teeth of the upper jaws and palate held firmly the struggling prey,
while the loosely united jaws, bending laterally at the joint back
of the middle, either alternately, or more probably in unison,
steadily forced it far enough back to be seized by. the muscles
of the fauces.

The shape of the mosasaurs, though slender, does not suggest
extraordinary speed in the water; doubtless most of the fishes
that lived in the seas with them could’ swim faster than they.
Their prey was captured, for the most part at least, by sudden
and quick lateral movements, for which their powerful and flexible
paddles admirably adapted them.

It isa rather remarkable fact that, among the thousands of.
specimens of mosasaurs which have been collected during the past
forty years in both Europe and North America, there never has
been found one of a very young animal. Of almost all other
animals occuring abundantly as fossils some specimens are sure
to be discovered of young and even embryonic individuals. It
is quite certain that all such voracious monsters as were the mosa-
saurs did not die of old age. Some specimens, it is true, have been |
found that were evidently not full-grown animals, but the observed
differences in the size of the fossil bones are not great. All are of
adult or nearly adult animals. If the mosasaurs were oviparous,
as were the ichthyosaurs, and probably the plesiosaurs, and as
are some living land lizards, the apparently entire absence of
embryonic bones associated with often nearly complete skeletons
of the mosasaurs is inexplicable; certainly some mosasaurs must
have died a short time before the birth of their young. But
embryos have never been discovered, though numerous skeletons
inclosing fossilized stomach contents have been found. From
this fact it would seem very probable that the mosasaurs were
164 WATER REPTILES OF THE PAST AND PRESENT

oviparous, as are most other lizards. But this, after all, may be
a hasty inference.

No known reptiles lay their eggs in the water. Perhaps there
is some reason why the eggs of reptiles and birds, so different from
those of fishes and amphibians, cannot hatch in water; and there
is no good reason for supposing that the mosasaurs were exceptions
to this rule. Unless carefully hidden or protected by the parent,
the eggs or very young of the mosasaurs would have been subject
to many and grave dangers. Fish eggs are usually small and pro-
duced in great numbers, thousands often being extruded from a
single female. Among so many there is a greater probability that
at least two will hatch and survive to maturity, reproducing their
kind. It is unreasonable to suppose that the lizards of the past
were more prolific of eggs than are their relatives now living; nor
is it possible that their eggs could have been as small as are those
of most fishes. Modern lizards seldom lay more than twenty-five
or thirty eggs at a time; even the turtles, with their greater vicis-
situdes, seldom produce more than one hundred. The eggs of
the mosasaurs were certainly large and few in number, and the
young animals must have begun breathing air immediately after
escaping from the shells. If the mosasaurs were oviparous they
must have laid their eggs upon the shores and beaches, as do the
sea-turtles and the Crocodilia. Nor is it at all probable that the
female mosasaurs gave even that protection to their eggs or
young that the crocodiles and turtles give. The young mosasaurs,
perhaps reaching a foot in length, must have been left entirely

‘to their own devices and their own fate at the very earliest stages
of their independent careers.

The waters in which the mosasaurs abounded swarmed with
many kinds of predaceous fishes, to say nothing of the hordes of
their own kinds, all carnivorous in the highest degree, to all of
which the tender saurians must have been choice food. Possibly
the shallow waters of the bays and estuaries may have afforded
protection to the newly hatched reptiles. It would seem probable
that the female mosasaurs went up the rivers for a shorter or longer
distance to lay their eggs or give birth to their young, and that the
young reptiles remained in such relatively protected places until
SQUAMATA 165

of a sufficient size to cope with the fierce enemies of the open seas.
We know practically nothing of the inhabitants of the lakes and
rivers during all the time in which the mosasaurs existed; and this
perhaps is the real reason why we have never yet found a specimen
of a young mosasaur.

We have seen that many skeletons of ichthyosaurs are found
entire, and but little disturbed in position, suggesting, if not proving,
that the animals as a rule lived and died far out in the deep seas,
away from the disturbing effects of currents of water on their
decaying bodies. Among the thousands collected, the great
majority of the specimens of mosasaurs consist of a few bones
or a part of the skeleton only. Moreover, nearly all specimens

 

 

 

 

 

Fic. 79.—Head of Tylosaurus

show the disturbing effects of currents of water; and the bones
are usually associated with those of turtles, birds, and flying reptiles,
which probably did not often venture far from the shores; all of
which goes to prove that the mosasaurs in general lived in the com-
paratively shallow waters of the seas, and not far from the shores.
That some were excellent divers, descending probably many
fathoms deep in the water, is certain, because of the extraordinary
protective structures of the eyes and ears.

But the various kinds of mosasaurs differed not a little in their
habits. Some, like Mosasaurus and Clidastes, were doubtless
chiefly surface swimmers, as is evidenced by their better ossified
bones, firmer articulation, and the presence of the additional
166 WATER REPTILES OF THE PAST AND PRESENT

zygosphenal articulations of the vertebrae, wanting in other forms,
as also by the structure of their paddles. They had a relatively
long body and short tail, the tail having a more pronounced distal
expansion than in the case of other forms, and the eyes looking
laterally, not at all upward. The feet, as shown in Fig. 74, were
broad and short, with most of the wrist and ankle bones well
ossified, and with but few extra bones in the digits. JTylosaurus
(Fig. 79), on the other hand, had a more slender skull, the nostrils
were situated farther back from the tip of the snout, the tail was
longer and more powerful, and the feet were very highly specialized
(Fig. 75). The wrist and the ankle were almost wholly carti-
laginous, the fifth finger and fifth toe were much longer, and the
number of phalanges was greatly increased. Moreover, the bones
of the skeleton are more spongy, the joints are more cartilaginous,
and the ears were better protected-by a heavy coat of cartilage.
In most of these respects the genus Platecarpus was intermediate
between Clidastes and Tylosaurus (Fig. 76).

Like nearly all other lizards, the mosasaurs had a pineal open-
ing in the skull, but it is not at all probable that they possessed a
functional pineal eye.

Many and varied have been the opinions of scientific men
regarding the relationships of these animals, as has been intimated.
They were thought to be a kind of whale or breathing fish by
Peter Camper; crocodiles, by St. Fond; and aquatic lizards, by
Adrian Camper and Cuvier. The late Professor Cope thought
they were more nearly related to the snakes than to the lizards,
and that they might even have been the ancestral stock from which
the snakes have descended. Because of this belief he gave to them
the name Pythonomorpha, meaning python-like, and ‘this name,
really the first ever applied to them, is yet often used instead
of Mosasauria. A more complete knowledge of the mosasaurs,
however, and especially the recent discoveries of the semiaquatic
connecting links, called the aigialosaurs and described on a pre-
ceding page, have set at rest all doubt as to their real affinities.
They are real lizards, differing less from the living monitor land
lizards than do the monitors from some other land lizards, espe-
cially the amphisbaenas and chameleons. And to Adrian Camper
SQUAMATA 167

is due the credit for the recognition of their real relationship,
though it required more than a century to prove that he was
right.

Very recently, and since the foregoing was written, a remarkable
new type of mosasaurs has been discovered in Alabama and Europe.
Only fragmentary jaws, a few vertebrae, and some skull bones are
known, so that it is impossible yet to decide how closely the new
form is related to the true mosasaurs, but so far as the evidence
goes the only distinguishable character is the teeth. These, instead
of being elongated and pointed, are nearly spherical, as shown in
Fig. 80. Such teeth could have been used only for crushing shell

 

Fic. 80.—Globidens alabamensis. Part of mandible, with teeth, natural size.
(From Gilmore.)

fish, and not at all for the seizure and retention of slippery fishes.
The genus, which was called Globidens by its discoverer, Mr. Gilmore,
includes two known species, from Alabama and Europe, the latter
recently described by Dollo. It has been suggested that this pecu-
liar kind of dentition was a more primitive or intermediate one, a
kind that the first mosasaurs had before they became fully adapted
to the water; but this is doubtful, since Globidens comes from late
Cretaceous, and must be one of the later types. If Globidens is a
true mosasaur, and it seems to be one, its life-habits must have
been remarkably different from those that have long been known.
Possibly when the limbs and more of the skull are found, Globidens
will prove to be of a distinctive type.
168 WATER REPTILES OF THE PAST AND PRESENT

SNAKES

The chief differences between snakes and lizards have already
been given and need not be repeated, save very briefly. Snakes
are always functionally legless, though some have vestiges of the
hind pair; the brain-case is wholly bony; the upper temporal bar
is wanting; the lower jaws are united in front by ligaments only,
like those of the mosasaurs; the vertebrae are greatly increased in
number, and always have the additional zygosphenal articulations
like those of Clidastes and Mosasaurus and some lizards; there is
but one lung, and the eyes are always without free eyelids. But
these characters are really not very important, since every one of
them is found in the lizards or mosasaurs, except the complete
ossification of the brain-case, and even this is partly ossified in
the mosasaurs. It is rather the presence of all these characters
which distinguishes a snake from a lizard.

The number of living snakes is nearly as great as that of the
living lizards, and their distribution over the earth is very similar.
Snakes are for the most part strictly terrestrial in habit. Some
live more or less among trees, and some live in the water, though
with but few exceptions all are fully capable of rapid progres-
sion upon land. They are almost invariably carnivorous in
habit, swallowing their prey whole, and usually alive, as has
been described. Some poison their prey or crush it to death before
swallowing it. Some feed upon eggs which are swallowed whole
and then crushed in their stomachs by projecting bones from the
under side of the vertebrae developed for that purpose. In size
snakes vary from a few inches in length to twenty-five or more
feet, no known extinct forms being larger than the living anacondas
and boas. In geological history the earliest remains known date
from the latter part of the Cretaceous, and it is quite probable that
they have a briefer history than that of the lizards of which they
are the descendants. Venomous serpents are known only from
comparatively recent geological times, and it is probable that
venomosity is the latest and final specialization of importance in
the reptilian class.

Of strictly aquatic snakes there is no known geological history,
and it is improbable that there is any such history. There are
SQUAMATA 169

a few snakes now living—very venomous ones, allied to the deadly
cobras—which have become so completely adapted to life in the
water that they are unable to exist or even move about on land.
These are the well-known sea-snakes of the Indian Ocean and
adjacent waters. Perhaps the most highly specialized and typical
of these is the black-banded sea-snake, Distina cyanocincta, which
reaches a length of four or five feet, and is a rapid and excellent

 

 

Fic. 81.—Hydrus bicolor; sea-snake. (From Brehm)

swimmer. From the figure (Fig. 81) it is seen that the body is
very much flattened from side to side, and lacks or has but a few
vestiges of the transverse scales on the under side so characteristic
of all other snakes, and which enable them to move about on land.
So helpless are these snakes on land that it is said sailors will handle
them carelessly, because of their inability to bite while out of water,
though the bite is very venomous. They never come on land for
any purpose whatever, and their young, unlike those of most other
170 WATER REPTILES OF THE PAST AND PRESENT

snakes, are born alive. There are a number of species of these
sea-snakes, though comparatively little is known of their habits.
They are of especial interest as another example of the ways in
which air-breathing land vertebrates have become adapted to’
water life. The adaptation, however, was simple, for nearly all
snakes swim freely in water by undulatory movements; it would
require not much change to convert an ordinary water snake into
one like these sea-snakes.
CHAPTER XII
THALATTOSAURIA

Millions of years before the first appearance of the mosasaurs
in geological history, another group of reptiles showing many
curious resemblances to them attempted a rather precarious exist-
ence in the water. Its members survived long enough to acquire
many structural adaptations to a water life, long enough to become
diversely modified, but not long enough, apparently, to wander far
from their birthplace, not long enough to attain that security from
their enemies and more ambitious competitors, the early ichthyv-
saurs and plesiosaurs, to insure them a long existence. They were
only a partial success as water reptiles.

It has been only within a few years that we have had any
knowledge whatever of them, and that knowledge is still very
incomplete, too incomplete to justify any attempt to picture them
as living animals, even though we take the liberties that some of
our illustrators of extinct animals feel warranted in assuming.
The first known specimens of these “‘sea-reptiles’—for that is the
meaning of the word Thalattosauria—were discovered and described
by Professor J. C. Merriam less than ten years ago, and all our
knowledge of these animals is due to the same author, who has
studied attentively the known specimens, all of which are pre-
served in the museum of the University of California. The first
discovered fragmentary specimens were confounded with those of
early ichthyosaurs, from the Upper Triassic rocks of northern Cali-
fornia with which they were associated. No specimen has yet been
found that is even approximately complete; some parts of the
skeleton are not yet known, even from fragmentary remains, and
not till other and more complete specimens have been found will
it be possible to determine the real form of the living animals or to
decide what their nearest relationships with other reptiles were.
Professor Merriam thinks that they were related most closely with

171
172 WATER REPTILES OF THE PAST AND PRESENT

the Rhynchocephalia (p. 176) of which the Sphenodon, or tua-
tera, of New Zealand is the only living representative, but whose
direct genealogical history runs back nearly or quite to the time
in which the thalattosaurs lived. On the other hand, there are so
many resemblances to the mosasaurs shown in the remains that
have been discovered, that it is possible the thalattosaurs were only
a short-lived branch of the primitive lizards, which we also know
were in existence at the time when the thalattosaurs lived. How-
ever, even though they resembled the mosasaurs, there could have
been no direct genealogical relationships between them, for it is
quite certain that the thalattosaurs very soon went out of exist-
ence, leaving no descendants. But it matters little which were
the land forbears of the thalattosaurs; they present such distinct
adaptations to water life—characters all their own—that their

 

Fic. 82.—Skull of Thalattosaurus. (After Merriam)

ancestral kinship may well be left to the future researches of the
curious paleontologist. For the present, at least, they may well
be placed in an order of reptiles all their own, as Professor Merriam
has proposed—the Thalattosauria.

No thalattosaurs were large animals. If they had the same
proportions between the lengths of head, body, and tail as the
mosasaurs, none exceeded seven feet in length, and they may have
been even shorter, though probably not much. The figure of the
skull, as restored by Professor Merriam, shows many striking
aquatic adaptations, in the elongated, pointed muzzle, in the large
external nostrils, situated far back toward the eyes, and in the well-
ossified ring of bones surrounding the eyeball. There is a parietal
opening in the roof of the skull, as in the modern lizards and
tuatera; but it is not known for certainty whether there were two
THALATTOSAURIA 173

openings on each side in the roof of the skull, as in the modern
tuatera. While this character may seem trivial, it is really one of
the most important in the reptilian anatomy in determining the
' relationship and classification of reptiles. The teeth are conical
and pointed in the front end of the upper and lower jaws, but
farther back they are rounded, rugose, and obtuse, and could
have been used only for crushing hard objects, like mollusks,
crustaceans, etc. (Fig. 82). And not only was there a row of such
teeth on each jaw (only partly seen in the figure), but similar
teeth covered a large part of the palate. And
the lower jaws, it is seen, are rather massive.
The vertebrae were, of course, of the more
primitive kind, that is, with the ends con-
cave, both in front and behind. It would
have been strange indeed were they of any
other kind, since reptiles with ball-and-socket
joints to the vertebrae, that is, concave on
one end and convex on the other, as in
nearly all living reptiles, did not come into
existence till long after the thalattosaurs had
disappeared from geological history; and it
s. as Fic. 83.—Dorsal ver-
is also a curious fact that such vertebrae Scag Heaibaie:
appear to have originated only among animals (after Merriam.)
crawling on land, so that they would not
have been a character acquired by the thalattosaurs after descend-
ing into the water. It will be seen from the figure of a dorsal
vertebra that the rib was attached by a single articular surface,
almost exclusively to the body of the vertebra, quite like those
of all lizards, snakes, and mosasaurs, and unlike those of other
reptiles. This too may seem to be a trivial character to prove
relationships with the lizards, but it is a curious fact that no two
animals having different kinds of ribs are closely related to each
other. Possibly, however, this looser mode of attachment of the
ribs in the thalattosaurs was one of their peculiar adaptations to a
water life, and may not have been derived from their land ancestors.
Of the limbs, only a few bones are known, but these are very
instructive. ‘The arm bones, as shown in Fig. 84, are strikingly

 
174 WATER REPTILES OF THE PAST AND PRESENT

like those of the mosasaurs, as will be seen by comparing the figure
on p. 157. The humerus is a little more elongated than that of
the mosasaurs, more nearly like the mosasaurian femur. The
shoulder-blade and the coracoid are imperfectly ossified, as is seen
from the figure—another characteristic of aquatic life. What the
fingers and toes were like cannot be said; probably, they were
bound together by membrane, forming
swimming paddles similar to those of the
mosasaurs. Some of the bones referred to
the pelvis are known, but it is not known
whether they are united to the spinal
column by a sacrum, as in land animals.
Nor is anything certainly known of the
hind leg or much of the tail. Since the
front legs show marked aquatic adapta-
tions, it is altogether certain that the hind
legs will be found to be modified more or
Fic. 84.—Thalattosaurus: less, though not so much modified as the
bones of front extremity: front legs, because, as we have seen, the
5, scapula; ¢, coracoid; #, front legs are always more specialized in
humerus; 7, radius; , ulna. Z i ;
(After Merriam.) aquatic animals than the hind ones, even
as the hind legs are more specialized than
the front ones in land animals. Possibly the hind legs will be
found to be more like those of the Thalattosuchia, as shown on
p. 212, that is, partly terrestrial in character. Doubtless the tail
was long and flattened, possibly with a terminal fin-like dilation,
though this is less probable.
As regards the habits and food of the thalattosaurs, no better
summary can be given than that of Professor Merriam, in his own
words:

 

The remains of thalattosaurs are known only in purely marine deposits
containing little or no material of terrestrial origin. They are associated with
a fauna consisting of numerous forms, both vertebrate and invertebrate,
which are not known to have existed away from marine areas. In the struc-
ture of the skeleton we find the abbreviated and broadened proximal segments
of the limbs, the slender snout with prehensile terminal teeth, and the median
superior nostrils, indicating a purely aquatic type. There can scarcely be
room for doubt that the thalattosaurs as a group were typical marine forms.
THALATTOSAURIA 175

The larger and more specialized species comprised in the genus Thalattosaurus
were strictly natatory. They may have visited the shore, but, like the plesio-
saurs, were better fitted for swimming than for crawling. Of the smaller
Nectosaurus we unfortunately do not know the limbs. They may have been
considerably less specialized, and the animal to a correspondingly greater degree
a shore-dweller. Nectosaurus is, however, found in the same deposits with
other forms and appears to be as common as the others; so that it is safe to
consider it as having passed the greater part of its life away from the shore.

From what we know of the vertebral column of Thalatiosaurus it appears
that the animal had a relatively short neck and a long dorsal region, the pro-
portions being nearly those in the vertebral column of some mosasaurs. Only
the anterior portion of the caudal region is known. The slender, rounded-neural
spines with well-developed articulating processes seen here ‘are not such as
commonly appear in forms with a highly specialized sculling tail, and it is
hardly probable that a caudal fin of large size was developed.

The anterior limbs evidently formed paddles of moderate size. The
posterior pair may have been larger, in compensation for lack of a strong scull-
ing tail. It is, however, possible, that as in Geosaurus (of the thalattosuchian
crocodiles) the hind limbs were not typically natatory, and the distal end of the
tail was vertically expanded.

No specimens have yet been found which are well enough preserved to
show any remains of the stomach contents, and we have no definite evidence
concerning the food of the thalattosaurs, more than is furnished by the general
structure of the animal. The character of the paddles, the form of the skull,
and the presence of slender prehensile teeth in the terminal portions of the
jaws would indicate that they fed in part upon some swiftly moving prey
which was caught by a quick snap of the jaws, deglutition being assisted by the
curved teeth of the pterygoids. The heavy vomerine and posterior mandibular
teeth may have been used for crushing the light shells of ammonites, which
existed in vast numbers in the same seas.
CHAPTER XIII
RHYNCHOCEPHALIA

In some of the small islands near the northeast coast of New
Zealand certain small and peculiar, lizard-like reptiles, known as
tuateras, have long been known. For many years they were sup-
posed, even by scientific men, to be real lizards, so much do they
resemble in external appearances and in habits the lizards of other
parts of the earth. It was early observed, however, that they
presented certain remarkable internal differences from the real
lizards or Lacertilia, though it was not till about twenty-five years
ago that the importance of these differences was recognized by the
late Professor Cope, who separated them into a distinct order quite
co-ordinate with the lizards, crocodiles, and turtles. These little
reptiles, seldom reaching a length of two feet, have now become so
scarce that the New Zealand government protects them by law
from unnecessary destruction; nevertheless it will probably be
only a short time before they become extinct, the end of a long
genealogical line. No other living reptiles have retained more of
the old-fashioned or primitive characters than this Sphenodon or
Hatteria, as the animal is called, and because of them it is of peculiar
interest to zodlogists, and especially paleontologists.

The differences of these beaked lizards from the true lizards
are especially noticeable in the skull, and more especially in the
arrangement of the bones which give articulation to the lower
jaws (Fig. 8). In the lizards and snakes the quadrate bone is
loosely articulated at its upper end with the cranium, and has no
inferior bar or arch connecting its lower end with the jugal and the
back part of the upper jaw. Sphenodon, on the contrary, has the
quadrate bone firmly fixed to its adjacent bones at both ends, and
is quite immovable. The vertebrae are biconcave like those of all
early reptiles, not concavo-convex as are the vertebrae of most
other living reptiles. The intercentra or hypocentra, little wedge-
shaped bones between the centra below, are more persistent in

176
RHYNCHOCEPHALIA 177

Sphenodon than in any other living land animals except the gecko
lizards. Upon the whole the tuatera is the most old-fashioned of
living reptiles, and in consequence it has nearly lost out in com-
petition with new things.

_ With these living tuateras we have nothing further to do, since
they are land animals, living about the beaches of the New Zealand
islands, and only occasionally venturing into the water, hiding from
their enemies in the holes in the rocks. But, from some of their
antecedents, from some of their direct forbears perhaps, there have
gone off at different times various branches, whose descendants
wandered into foreign lands or into foreign places, and lived and

 

Frc. 85.—Sphenodon punciatum, or tuatera. (From specimen in the Yale Uni-
versity museum.)

flourished for a brief time and then became extinct. Some of these
went down into the water and became more or less aquatic in
habit; some, indeed, changed their forms and habits so greatly
that they are often, perhaps rightly, segregated into different
orders. Whether or not they should be called Rhynchocephalia
matters little, however. It is merely a matter of opinion as to
how great the changes should be in order to entitle the offspring
to a genealogical tree all its own.. Of these branches there are
two, whose relationships seem to be definite, the Choristodera and
Thalattosauria, though there is more doubt about the latter than
the former. A third group, that included Pleurosaurus, seems, from
178 WATER REPTILES OF THE PAST AND PRESENT

more recent discoveries, to belong to a different line of descent and
has been described under the Protorosauria.

In the direct line of ancestry there is no known form that was
distinctly aquatic. The oldest known of these, perhaps, is that
shown in Fig. 86, Saphaeosaurus from the Jurassic of Solenhofen.
Its resemblance to the modern
tuatera is great, and doubtless its
habits were very similar, though its
rather long tail and rather short neck
possibly indicate subaquatic habits.

 

CHORISTODERA

Among the many reptiles of the
past which have sought a more con-
genial or a safer home in the water
few have had a more interesting his-
tory, or a briefer one, than those to
which the late Professor Cope gave
the name Choristodera in 1876.
Many students of repute consider the
group an order, others a suborder
of the Rhynchocephalia. The group,
whether order or suborder, are inter-
esting because. of their long and
devious migrations from western
North America to Europe, or vice
versa, through rivers and ponds;
interesting also because of the per-

sistence of certain old-fashioned traits
Fic. 86.—Sapheosaurus, an ‘
Upper Jurassic rhynchocephalian. that clung to them long after their
(After Lortet.) disappearance in other animals.
Perhaps these traits were among the
causes of their merely moderate success as animals of the water,
traits that led to their early dissolution. Like the proganosaurs,
which they must have resembled in external appearance not
a little, they wandered from their birthplace in the western
continent, to perish in the eastern; and like them their span of
existence was short.

 

 

 

 
RHYNCHOCEPHALIA

Their history among man-
kind, too, is brief. The first
known specimens, from western
North America, were described
by Professor Cope in 1876,
under the name Champsosaurus.
In the following year Professor
Gervais of Paris made known
another form from Rheims,
which he called Simoedosaurus,
so closely allied to the American
that even yet they have not
been sharply distinguished.
Some years later these European
specimens were more fully de-
scribed by the well-known
Belgian paleontologist, Dr.
Dollo, but it has been only
within the past few years that
our knowledge of the animals
has been made at all complete
by the discovery and description
of several excellent skeletons of
Champsosaurus by Mr. Barnum
Brown of New York.

These semiaquatic reptiles
never grew very large—not more
than four or five feet in length;
nor did they ever succeed in
becoming fully at home in the
water, certainly no more so than
our modern alligators and croco-
diles. They remained to the
end of their comparatively brief
existence essentially land ani-
mals, probably seeking their
food in the water but fleeing to
the land for protection and for

 

 

179

 

 

 

 

Fic. 87.—Champsosaurus; skeleton, as
mounted in American Museum. (Brown.)
180 WATER REPTILES OF THE PAST AND PRESENT

the breeding of their young. Their chief water adaptations are
seen in the elongate face and flattened swimming tail. Their legs
remained essentially terrestrial, and could have been of but little
use in the water for propulsion; the feet even were doubtfully
webbed, or if so, not more than are those of the alligator.
Singularly, like the proganosaurs, their ribs were heavy and
stout, also suggesting bottom-crawling habits, like those of the

 

 

 

Fic. 88.—Restoration of Champsosaurus

living Galapagos lizards. The skull was lightly built, and the face
_was long and slender, like that of the gavials and proganosaurs;
but, like those of the former and unlike those of the latter, the
nostrils were situated at the extreme tip. The hind legs were
firmly attached to the body by the sacrum; and no sclerotic bones
of the eyes have been discovered. The neck was neither unusually
long nor unusually short. The body was probably covered with
horny scales.
RHYNCHOCEPHALIA 181

To the student of paleontology these animals are of interest
because of the retention of several primitive traits which had long

 

Fic. 89,—Champsosaurus; skull from above. (After Brown)

disappeared in other known reptiles. While the vertebrae had
ceased to be perforated by the notochord, as in the-early reptiles,
they were still shallowly biconcave. The first bone of the neck,
182 WATER REPTILES OF THE PAST AND PRESENT

the atlas, had changed but little from that of their very ancient
forbears of Permian times, and the bones of the palate still retained
numerous teeth scattered over it, like those of the same Paleozoic
ancestors. Most primitive and old fashioned of all was the pelvis,
which was so unlike that of all known contemporary or later
reptiles that, were a
paleontologist to see
it without knowing
_whence it came, he
would be almost sure
to say that it belonged
to a Paleozoic, or at
least a Triassic, reptile,
and not only to an
early reptile but a very
primitive one at that.
This peculiarity con-
sists in the absence of
any opening between
the ischium and pubis, which is characteristic of every living verte-
brate with legs. And these and other old-fashioned characters
could not possibly have been new developments; they must have
existed in all the ancestors of the Choristodera from Paleozoic to.
early Tertiary times, though not a single
other reptile is known to have pos-
sessed them, for the greater part of
this time. Perhaps when Asia and
northwestern America have been more
thoroughly explored for vertebrate fos-
sils, some of their ancestors which per- sue aos
ished on their great migration from the pelvic bones. (After Brown.)
western to the eastern continent in

late Cretaceous times will be discovered.

The choristoderans began their existence, so far as is now known,
in North America in late Cretaceous times and died out in both
Europe and North America in early Tertiary times. That is, they
were one of the few branches of reptilian life which not only wit-

 

Fic. 90.—Pectoral girdle of Champsosaurus. (After
Brown.)

 
RHYNCHOCEPHALIA 183

nessed the extinction of the great dinosaurs and plesiosaurs, but
the advent also of the early placental mammals. They lived mil-
lions of years after the proganosaurs became extinct, and, similar
as they are in form, there is no relation between them. Moreover,
in all probability they did not migrate to the eastern continent over
the same route.

The structure of the head and teeth of the Choristodera clearly
indicates a fish-eating habit, or at least a diet of soft-bodied, free-
swimming invertebrates. The legs and ribs, as also the armor of
ventral ribs, like those of the plesiosaurs, point very insistently
toward a bottom-crawling habit while in the water.
CHAPTER XIV
PARASUCHTIA

The first known specimen of the order of reptiles now generally
known as the Parasuchia was found in Wiirtemberg, Germany, in
1826 and very briefly and inadequately described’ two years later
by Professor George Jaeger. The specimen was a sorry one, and
was sadly misinterpreted by Jaeger. It consisted chiefly of casts
of the alveoli or sockets of a number of teeth, more or less con-
nected by corroded or decomposed portions of the jaws. He
recognized the casts as teeth of a peculiar reptile, but mistook the
roots for crowns, and, naturally concluding that such obtuse teeth
would be of use only for the mastication of vegetable food—about
the last kind of food to which the phytosaurs were addicted—
called the animal Phytosaurus, meaning plant saurian. Because of
differences he observed in the shapes of the teeth he thought that
they belonged to two distinct species, which he called cylindri-
codon and cubicodon; but the differences were due simply to the
different positions they held in the jaws.

Fourteen years later Hermann von Meyer, the renowned Ger-
man paleontologist, described and figured other remains of the
same or an allied reptile under the name Belodon plieningeri. In
subsequent papers during the next twenty-three years von Meyer
very fully described and beautifully illustrated the skulls and other
remains of this and other species, all of which he referred to the
genus Belodon, the name by which for many years the animals

t“The author showed drawings and some specimens of two hitherto unknown
reptiles from the white, coarse-grained sandstone, of which one in the form of the skull
resembles the gavial, but is distinguished by the cylindrical form of the lateral teeth
of the jaws; he therefore calls it provisionally cylindricodon, and a second species or
genus, of which, however, so far only fragments of the jaws have been found, because
of the four-cornered form of the teeth, cubicodon, while at the same time for the genus
or family, to which the remains of these animals have belonged, he proposes the name
Phytosaurus, since the teeth seem to be more adapted to a vegetable diet, even though
they have not been worn away, as in Igwanodon.’’—Isis (1828), p. 441 (translation).

184
PARASUCHIA 185

were generally known in scientific literature. Von Meyer thought
that he recognized in Belodon kapfii, the species most often
figured in textbooks, the same animal that Jaeger had previously
described.

Von Meyer was not at all certain about the relationships of his
Belodon, though he recognized its affinity with the crocodiles. It
was Huxley who, in a famous paper on the evolution of the croco-
diles, published in 1875, united Belodon and another genus from the
Trias of Scotland, which he called Stagonolepis, with the Crocodilia
as representatives of the suborder Parasuchia, one of the three into
which he divided the order. Huxley admitted that the relation-
ships between the Parasuchia and the Mesosuchia or Eusuchia, the
other suborders which he proposed, were not as intimate as those
between the latter two, which were separated solely on the structure
of the palate and vertebrae, as has been explained in chap. xv.
As early as 1869 the late Professor Cope recognized certain forms
which had been previously described from Carolina as belonging
to the group, calling them Belodon, but it was not until 1896 that
E. Fraas séparated Belodon planirostris of von Meyer as a member
of a distinct genus, to which he gave the name Mysiriosuchus.

Here, as a part of the order Crocodilia, the phytosaurs remained
till within very recent years, though there have been some mild
protests against the association, especially by Marsh, Zittel, and
Baur. The famous English paleontologist, Richard Owen, located
the ‘‘Belodontia,” as the phytosaurs were often called, in his order
Thecodontia, based chiefly upon the manner of the insertion of
the teeth in sockets. But this has long since been shown to have
little value in the classification of reptiles. Various authors have
written about the phytosaurs in later years, notably Cope, Fraas,
Huene, and Jaekel, but it was J. H. McGregor who first definitely
separated the phytosaurs into a distinct order, in a careful revision
of the American forms. He called the order Parasuchia, after
Huxley, dividing into two suborders, the Phytosauria, after Jaeger,
and the Aetosauria, a group which, for lack of a better place, had
previously been classed with the Crocodilia, either as a member
of the Parasuchia or as an independent suborder by Zittel (the
Pseudosuchia). More recently Huene has shown that certain
186 WATER REPTILES OF THE PAST AND PRESENT

African reptiles from the Lower Trias had certain very definite
characters entitling them to an independent position, for which he
proposed the order Pelycosimia. Upon the whole, however, these
characters seem to be primitive parasuchian, and the group may
provisionally be placed in the order Parasuchia, as a third suborder,
the Pelycosimia. The order Parasuchia, then, until we know much
more about the latter two groups, may be conveniently divided
into three suborders, the Phytosauria, Aetosauria or Pseudosuchia,
and the Pelycosimia, all of Triassic age.

McGregor was quite right in retaining for the suborder the
name Phytosauria, suggested by Jaeger in 1828, inappropriate as
the word is etymologically, but was hardly justified in substituting
the generic name Phytosaurus for the long and well-known Belodon,
because it is quite impossible to say that Jaeger’s very fragmentary
specimen upon which he based the genus Phytosaurus really is the
same as Belodon. Professor Fraas very kindly showed the writer
the original type-specimen of Jaeger, now preserved in the Stutt-
gart Museum, and both are agreed that it is impossible to prove
the identity of Belodon and Phytosaurus from the very fragmentary
and imperfect specimen. It is quite as probable, for instance, that
Phytosaurus and Mystriosuchus are identical as that Phytosaurus
and Belodon are. Unfortunately, this is not the only case in ver-
tebrate paleontology where the fragmentary specimens to which
names have been given are inadequate to determine the species,
or genus, or even the family to which they belong; there have
been very many such instances. The pioneers in paleontology
were often justified in naming small and obscure fragments of
bones, or single bones. One would be justified even yet in giving
a name to an indeterminable fragment of a bird bone from the
Triassic formation, because the discovery of a bird of any kind in
that formation would be very important for science, even if its
precise kind might never be recognized from the specimen.
Nevertheless, the custom is a very reprehensible one when indis-
criminately followed. For these reasons the writer disagrees with
McGregor in substituting the inappropriate name Phytosaurus for
Belodon, the name by which the most typical forms were so long
known.
PARASUCHIA 187

The Aetosauria, which have long been known from a marvelous
specimen found in Wiirtemberg many years ago and described by
the elder Fraas, need not detain us long. They were relatively
small reptiles about two feet long, almost completely incased in a
bony armor, and purely terrestrial in habit. The skull even yet
is not perfectly known, and it is possible that when it is the group
may have to be dissociated from the phytosaurs. The nostrils
were not posterior, and the skull is short. Other specimens of the
same group have been described from the Upper Triassic rocks of
Massachusetts. :

The Pelycosimia of Huene are very interesting as showing
apparently primitive forms with which the true phytosaurs may
have been intimately related ancestrally. They, too, have a rather
short skull with the nostrils in front, and were not at all aquatic in
habit. ‘Not much is known about the single genus that is located
in the group, aside from the skull and a few limb bones.

4

PHYTOSAURIA

The Phytosauria, so far as known, were all reptiles of consid-
erable size, greatly resembling the crocodiles, and especially the
gavials in form and habit, but differing very greatly in having the
external nostrils situated far back near the eyes; in having no
false palate so characteristic of the Crocodilia; in having a more
primitive shoulder-girdle, consisting of a short coracoid, inter-
clavicle, and clavicles; and in having the ordinary type of pelvis,
that is, with the pubis entering into the acetabular articulation
for the femur. They were all, like the crocodiles, covered more or
less by a bony armor; there are two openings on each side of the
temporal region; there is no pineal opening; the vertebrae are
gently biconcave, precisely like those of the early or mesosuchian
crocodiles; there is always an opening of considerable size, called
the preorbital foramen, in front of the eyes, as in some crocodiles,
many dinosaurs, and most pterodactyls; there is also an opening
through the back part of the mandibles as in crocodiles; and the
double-headed ribs are attached exclusively to the transverse
process of the arch, precisely as in the crocodiles, dinosaurs, and
pterodactyls. From all these it is evident that the phytosaurs are
WATER REPTILES OF THE PAST AND PRESENT

188

 

 

AnesoyAyd oissersy, addy ue ‘snyansorasc py Jo uotye10}say— 26 *91,J

 

 

 
related most nearly
to the crocodiles and
dinosaurs, and are
probably an early
branch of the stem
from which they, the
pterodactyls and the
birds, arose, a branch
that persisted only a
short time, geologi-
cally speaking, and
went entirely out of
existence at the close
of Triassic times,
leaving no descend-
ants behind. Never-
theless, in this
comparatively _ brief
life-span they devel-
oped not a few dis-
tinctive forms and
became widely dis-
tributed over the
earth. Their remains
are known from the
Upper Trias of Ger-
many, England, and
Scotland, India,
South Africa, and
from Massachusetts,
North and South
Carolina, and many
places in the Rocky
Mountains. No true
phytosaurs are yet
known from South
America, but in all

PARASUCHIA 189

 

 

 

 

 

Fic. 93.—Skull of Mystriosuchus, a phytosaur: pm,
premaxilla; m, maxilla; na, nasal; f, frontal; , pre-
frontal; /, lacrimal; pf, postfrontal; po, postorbital;
pa, parietal; sg, squamosal; gj, quadratojugal;
pl, palatine; #, transverse; im, interna] nares; en,
external nares; pf, pterygoid; bs, basisphenoid; eo,
exoccipital. (After McGregor.)
i
Igo WATER REPTILES OF THE PAST AND PRESENT

probability they will be discovered there when the Triassic deposits
of that continent have been better explored for fossils. In the
Rocky Mountains, especially, their remains are widely scattered,
they have been found in many localities in Wyoming, Colo-
rado, Oklahoma, Utah, and New Mexico. Though for the most
part their known remains from these localities are yet fragmentary,
not less than four distinct genera have been described from these

         

why

et

i) o

     

Fic. 94.—Dorsal vertebrae of phyto- Fic. 95.—Scapula and coracoid of
saur: az, anterior zygapophysis; pz,pos-  Rutiodon carolinensis, an American phy-
terior zygapophysis; d, ¢, articulations tosaur. (After McGregor.)
of rib.

regions: ‘“‘Belodon,” Angistorhinus, Paleorhinus, and Episcopo-
saurus. From the Carolinas and Massachusetts a single genus,
‘though described under numerous names, has been made known,
originally called by Emmons Rutiodon (Rhytidodon). And from
Europe and India at least as many more different genera are known.
All these genera are, however, so closely allied that they are placed
in the single family Belodontidae.
PARASUCHIA IQI

In Belodon (Fig. 96), the earliest known and most typical
genus, perhaps, the moderately elongated face has a high crest
reaching nearly to its front end, and this type is known both from
Europe and from New Mexico.
Others have the face long and
slender, even longer and more
slender than in the ancient teleo-
saur crocodiles or the modern

 

 

 

 

 

 

 

 

 

Fic. 96.—Belodon; restoration of head, Fic. 97.—Mystriosuchus; restoration
from above. of head, from above.
192 WATER REPTILES OF THE PAST AND PRESENT

gavials. In some forms the teeth are cylindrical and slender
throughout, and there may be as many as fifty on each jaw, or
two hundred in all; while in others only the anterior teeth are
cylindrical and the posterior teeth are flattened and serrate along
their cutting edges. In the body not very great differences have
been observed. Some are more slender than others, and there are
minor differences in the shapes and sizes and numbers of the bony
scutes along the back and on the throat.

But they are all alike in their essential characters, a very long
beak with numerous teeth; the foremost ones on the expanded,
more or less spoon-shaped front extremity, are more or less, some-
times greatly, elongated. The jaws may be likened to a long and
slender pair of tongs with nipping teeth at the front end. The
strong, long, and flattened tail is sufficient evidence that the phy-
tosaurs were excellent swimmers, but, aside from that and the
posterior location of the external nostrils, directly over the internal,
few other aquatic adaptations are observed in the skeleton. There
are no sclerotic bony plates about the eyes, or at least none have
so far been discovered, although among the numerous known speci-.
mens they would confidently be expected were they really present
in the skeleton; and the presence of bony armor negatives markedly
aquatic habits.

Doubtless on the whole the habits of the phytosaurs were not
very unlike those of the modern gavials, which they so strongly
resemble in form, size, and general characters. But they differ
very greatly from the gavials in the extreme posterior position of the
nostrils, and in the greatly elongated teeth of the front end of the
beak, teeth which must have had some especial and peculiar use.
Nor is the position of the nares to be accounted for satisfactorily
by reference to aquatic habits. It has been suggested that the’
creatures used the very long and slender beak in prodding and
probing in the sand and mud for soft-bodied invertebrates, worms
and the like, for which the teeth would be especially fitted; and
that the posterior position of the nostrils may be in part, perhaps
wholly, accounted for by this habit, which permitted the reptiles
to breathe without extricating the beakfrom the mud or shallow
waters. That the animals were wholly and intensely carnivorous
PARASUCHIA 193

in habit is attested by their teeth; although they are called “plant
saurians,” they never had anything to do with plants in the way
of food. Unfortunately so far no specimens have ever been found
showing the remains of stomach contents, nor have any been found
showing impressions of the form of the body or of any of its parts.
Until such specimens are found, as they doubtless will be eventually,
one can be less sure of the precise details in their life reconstructions.
However, the skeleton is now known nearly completely, and this
suffices to give a very approximately correct idea of what the ani-
mals were like when alive.
CHAPTER XV
CROCODILIA

The order of reptiles to which the name Crocodilia is technically
applied comprises less than twenty-five living species, popularly
known. as crocodiles, alligators, caimans, and gavials. They are
often of great size, ugly and repulsive in appearance, cruel and
vicious in habit, wholly carnivorous, and denizens, almost exclu-
sively, of fresh-water lakes or rivers in tropical and subtropical
regions; a few only venture into the sea near the shores. They are
all excellent and powerful swimmers, but are by no means exclu-
sively aquatic in habit, many of them spending a large part of the
time on the shores; and they invariably seek the land for the
deposition and hatching of their eggs. In size they are the largest
of living reptiles, some of the existing species reaching a length of
twenty-five feet, while some extinct species were probably fully
twice that length.

The geological history of the crocodiles is a very ancient one,
reaching back at least as far as the early Jurassic and probably to
the Triassic. The culmination of the order, at least so far as size,
variety, and numbers are concerned, was doubtless before the close
of the Mesozoic. The early crocodiles, however, were of a more
generalized structure in some respects, though specialized in others,
because of which naturalists in the past have usually divided the
order into three or four chief subdivisions, or suborders, two of
which, the Mesosuchia and the Thalattosuchia, became extinct
before or during Cretaceous time. The third suborder, the Para-
suchia of many textbooks, has now been unanimously separated
by paleontologists from the Crocodilia as an independent order.
The fourth suborder of the textbooks, the Eusuchia, a word meaning
true crocodiles, appeared in geological history, so far as we yet know,
shortly before the extinction of the Mesosuchia, and is best known
from the forms now living, all of which belong to it. Although the

104
CROCODILIA 195

modern crocodiles can hardly be called, as a group, purely aquatic
reptiles, we shall find it of interest, because of their intimate rela--
tion to the older and more strictly marine forms, to speak of them
somewhat in detail.

MODERN CROCODILES, EUSUCHIA

The crocodiles of the present—and we use the word in the
technical sense of Crocodilia—because of their general resemblance
to the lizards, or true ‘‘saurians,’’ were classed with them by the
older naturalists, whence comes the popular name alligator, a cor-
ruption of the Spanish el lagarto, or ‘‘the lizard,” given to some of

 

 

 

Fic. 98.—Senegal crocodile. (By permission of the New York Zodlogical Society)

the South American forms by early explorers. But this resem-
blance is a superficial one only, as was early recognized by com-
parative anatomists. The crocodiles, indeed, are only remotely
related to the lizards.

The head or cranium is flattened and broad, the facial part or
snout sometimes greatly elongated and slender, and the external
nostrils are always situated at the front end. The bones of the
upper surface of the cranium and face have many pit-like depres-
sions. The neck is short and stout, and but little movable. The
body is somewhat depressed and flattened, not cylindrical and
slender, as in the more typical water reptiles. The tail is much
elongated and compressed, forming a powerful means of propulsion
196 WATER REPTILES OF THE PAST AND PRESENT

in swimming, its breadth being increased by a vertical row of horny
plates above. The limbs are of the ordinary elongated type—
ambulatory rather than swimming legs—and are not of much use
for propelling the body in the water; the front legs indeed are
usually held close to the body while the animal is swimming.
The toes, however, are partially connected by webs, to a slight
extent only in the alligators and crocodiles, but much more so in
the long-snouted gavials. The feet have five toes in front and
four behind; and the loss of the fifth toe can only be ascribed
to terrestrial habits. The body is covered more or less with horny
scutes or scales, beneath which are several rows of thickened,
pitted, bony plates on the dorsal side, and sometimes also on the
under side, forming a more or less extensive bony armor. The
eyes have movable lids, as in most lizards, and the ear-opening is
small.

But the external appearance of these reptiles is not sufficient
to distinguish them widely from other groups, and we must resort
to the internal structure, especially that of the skeleton, for the
more essential differential characters. The most crucial of these,
the one which more than any other determines their relationships,
consists in the position and shape of the bone with which the lower
jaw articulates, the quadrate bone, so characteristic of reptiles.
As in the plesiosaurian and ichthyosaurian skulls, it is firmly united
with the adjoining bones, not articulating freely with them, as in
the lizards and snakes. But this fixed relation of the bones is very
unlike that of the plesiosaurs, ichthyosaurs, and turtles, in that it
is held in place by two bony bars or arches, the upper extending
forward to unite with the bones at the back part of the orbit, the
lower, with the hind extremity of the upper jaw. The lower jaws
are rigidly united in front, sometimes for a long distance; they have,
almost always, a hole or opening through the hinder part, known
in but few other reptiles. The bones of the palate are all firmly
united, forming a nearly complete roof, very unlike the condition
in the mosasaurs and lizards. The palate also is very peculiar
in the development of a plate of bone below the nasal, chambers,
forming a complete bony canal on each side through which the
respiratory air passes far back to the internal opening of the nostrils
CROCODILIA 197

above the pharynx, and not, as in other reptiles—save the imme-
diate ancestors of the mammals—entering the mouth at the front
end. This peculiar arrangement of the air-passages, so like that of
ourselves, has much to do with the water habits of the crocodiles,
as we shall see.

The teeth are conical in shape, and are always restricted to the
edges of the jaws, above and below. They are inserted deeply and

\ |

eh

Fic. 99 Fic. 100

 

Fic. 99.—Skull of Alligator mississippiensis, from below.

Fic. 100.—The same, from above: bo, basioccipital; bs, basisphenoid; f, frontal;
j, jugal; 1, lacrimal; m, maxilla; 1, nasal; ~, parietal; pa, palatine; pm, premaxilla;
pf, prefrontal; pr, postfrontal; pt, pterygoid; g, quadrate; qj, quadratojugal; i,
transverse.

firmly in sockets, and are replaced frequently by new ones growing
beneath them, pushing the older ones out as their usefulness becomes
impaired by injury or by use. In some species there are as many as
thirty teeth in each side of the jaws, above and below, although the
broad-headed kinds have a smaller number.

The neck is short, as has been stated, but it always includes
in living forms nine vertebrae, a number probably slightly in excess
of that of their terrestrial forbears. By the peculiar mode of
198 WATER REPTILES OF THE PAST AND PRESENT

attachment of the short ‘‘hatchet-shaped” ribs, much lateral
movement of the neck is prohibited, nor is any very great vertical
movement possible. The vertebrae of the whole column, save the
atlas, the second sacral, and the first caudal—which is a very re-
markable anomaly—are concave in front and convex behind, agree-
ing in this respect with those of all other living reptiles, save the
turtles, the tuatera, and some lizards. The ribs of the neck have
their two heads attached, one to the body of the vertebra, the
other to‘the arch, but those of the dorsal region, though double-
headed, have both become attached to the transverse projection of
the arch, a seemingly trivial character, but one which immediately
distinguishes all crocodiles from all other water reptiles, and from all

 

Fic. 101.—Vertebrae of gavial from the side (cervical), and from-in front (dorsal) :
az, anterior zygapophysis; 2, posterior zygapophysis; d, diapophysis; 7, cervical rib;
¢, articulation for head; #, for tubercle of dorsal rib.

terrestrial reptiles, indeed, save the Parasuchia, Pterosauria, and
Dinosauria. The pelvis is firmly attached to the spinal column by
two sacral vertebrae.

The collar-bones, or clavicles, are wanting in crocodiles; there
is a slender interclavicle; and the shoulder-blade and coracoid are
well developed (Fig. 102). The bones of the pelvis are loosely
united with each other as they are in most reptiles (Fig. 104). The
pubes, the anterior bones below, unlike those of all other reptiles,
do not help to form the acetabulum or socket for the articulation of
the thigh bone, nor do they articulate with each other. This
single character sharply distinguishes a crocodile from all other
reptiles, living or extinct, and is almost the only character that
CROCODILIA 199

separates the order from the dinosaurs, aside from the peculiar
structure of the nasal passages in the skull. On the under side of
the body, connected with the front end of the pubes, there are seven
or eight pairs of abdominal ribs, corresponding to the plastron of
the turtles and similar to those of the ichthyosaurs and plesiosaurs.
The mosasaurs have no such ribs.

  

Fic. 102

Fic. 102.—Scapula (sc) and coracoid (cor) of gavial.
Fic. 103.—Front foot of crocodile: ~, ulna; 7, radius; re, radiale; we, ulnare;
?, pisiform.

Furthermore, the crocodiles differ from all other living reptiles
in having a four-chambered heart, like that of birds and mammals,
that is, a heart with two auricles and two ventricles. This more
perfect structure of the circulatory organs does not, however,
insure at all times a complete separation of the pure or arterial
blood from the impure or venous blood, since the blood may be
more or less intermixed outside of the heart by a connection between
the venous and the arterial systems. Whether these imperfectly

5
200 WATER REPTILES OF THE PAST AND PRESENT

developed organs, so suggestive of a higher and more perfect mode
of respiration, are the vestiges of what were once among some
reptiles functional structures, or whether they are rudiments of a
higher organization, developing independently in these creatures,
cannot be positively determined, but it seems very probable that,
far back in geological times, some reptiles, especially the pterodactyls
and dinosaurs, had their respiratory and circulatory systems more
like those of the birds and mammals of today. Unfortunately,
however, if such was the case, we may never be able to prove it,
* although proof would not be impossible; stranger things than
fossil hearts have been found by
paleontologists!

The stomach, moreover, in
the crocodiles is fashioned some-
what after that of the birds,
with an imperfect division into
crop and gizzard. Some croco-
diles of today have the habit of
swallowing hard pebbles, as do

Fic. 104.—Pelvis of crocodile: i, ilium; many birds. There is an old
is, ischium; pu, pubis. myth that the crocodile of the
Nile swallows a pebble on each
of its birthdays, thus giving reliable information as to its age by
the number found in its gizzard at its death! And this habit has
been suggested for some of the most ancient crocodiles, the teleo-
saurs, by the recurring presence of siliceous pebbles found with
the remains of their skeletons. And we have seen this pebble-
swallowing habit was also characteristic of the plesiosaurs, with
whose remains ‘‘stomach-stones,”’ or gastroliths, as they have been
called,‘are often found.

All of these various characters of the skeleton and fleshy parts
are pretty conclusive evidence that the crocodiles, ugly creatures
that they are, today enjoy the highest rank among cold-blooded
animals. They are perhaps in some respects of not so high a type
of reptiles as were some of the extinct reptiles, but that they have
survived so long, so many millions of years, is pretty good evidence
of endurance, to say the least.

 
CROCODILIA 201

Living crocodiles belong to three distinct groups or families:
the true crocodiles and alligators; the long-snouted crocodiles or
Borneo gavials; and the true gavials of India. Members of the
first of these families are really only subaquatic, or amphibious in
habit; they move about on land with entire freedom, and often
seek their food there. Certain marked aquatic characters they do
possess, in the skull and tail, as we shall see. They are indigenous
to southern China, India, Africa, Madagascar, the southern part
of the United States, Central America, and the northern part of
South America. The members of this family are distinguished.
by the more or less broad and flat head, the possession of com-
paratively few teeth of large size, and by having the toes less
completely webbed. The crocodiles proper differ from the caimans
and alligators especially in the arrangement of the teeth. During
later geological times, that is, during early Tertiary times, the
geographical range of the Crocodilidae was much more extended
than it is at present, the remains of many often very large species,
being found in the lake deposits of the northwestern parts of the
United States, Great Britain, Germany, France, etc. Yet earlier,
in the late Cretaceous rocks of the United States, in Texas, and
Wyoming especially, there have been found rather scanty remains
of a gigantic crocodile which must have been nearly fifty feet in
length when living.

The second family, the Tomistomidae, or long-snouted croco-
diles, comprises but two living species, both restricted at the
present time to Borneo. These crocodiles have a moderately
slender snout, because of which they are sometimes called gavials,
though it is not nearly so slender as that of the true Gangetic
gavial. This family is probably older than either of the other
living ones, and is the only one known with certainty to have
lived during much of the Cretaceous times, several species of
considerable size having been found in New Jersey and Europe.
Their feet are better webbed than are those of the true crocodiles
and alligators, the front feet partly, the hind feet wholly so.
In general structure they seem to be the most primitive of the
living Crocodilia, and may have been the ancestors of all modern
forms.
WATER REPTILES OF THE PAST AND PRESENT

202

(Aya190G [ed1B0]90Z FIOA MON 9q} Jo uorsstuszed <q)

‘Telavg— Sor

‘Oly

 

 
CROCODILIA 203

The third family, the Gavialidae, also comprises but two living
species, both restricted in habitat to the rivers of India. Of these
the famed gavial of the Ganges is the better known and the more
highly specialized. The skull of this species has an exceedingly
long and slender snout; the teeth are numerous, small, and slender;
and the feet are more fully webbed than are those of other members
of the order. In habits the gavials are more distinctly aquatic
than are the crocodiles and alligators. They feed almost exclu-
sively upon small fishes, for the seizure and retention of which their
small and sharply pointed teeth are admirably adapted. The
hind feet are relatively long, a character that will be better under-
stood when comparison is made with those of the Thalattosuchia.
Although attaining a large size, fully twenty-five feet in length,
they are comparatively harmless animals, never attacking human
beings or other large animals, as do some of the crocodiles proper.
The gavials have lived a long time in the Indian regions, the
Gangetic gavial itself having been found in deposits of Pleiocene
age, perhaps the oldest known of all living species of air-breathing
vertebrates. Some of the extinct gavials of the same region
attained a length of nearly or quite fifty feet, possibly the longest,
if not the largest, of all swimming reptiles of ancient or modern
times. Extinct gavials have been reported from South America,
but are not yet fully known.

While the fish-eating gavials swallow their prey whole, the
crocodiles, caimans, and alligators prey upon all living animals that
come within their reach, whether large or small, and they will often
leave the water to seize their intended victims, such as pigs, sheep,
birds, or even human beings. Their teeth, as has been already
stated, are much larger, longer, and more irregular in size than
those of the gavials. Their victims are often drawn under the water
and drowned, the peculiar posterior position of the internal nos-
trils permitting the animals to breathe with the mouth and to
firmly hold their prey under water, while the extremity of the snout
and the external nostrils are above the surface.

As the firm, unyielding bony palate, the fixed position and
articulation of the lower jaws, and their rigid attachment to each
other in front do not permit creatures of large size to enter the gullet
204 WATER REPTILES OF THE PAST AND PRESENT

whole, the crocodiles and alligators must tear their food to pieces,
which they do by quick, strong jerks from side to side, aided by the
powerful tail; or they may twist off a limb or some other part of
their victims by a rapid rotation of the whole body, two assisting in
this operation, rotating in opposite directions.

Living crocodiles lay from twenty to sixty eggs, according to the
species; these eggs are sometimes the size of a goose egg, and are
covered with a hard shell. They are laid either in a deep excava-
tion in the sand and covered over by the parent; or under leaves
and straw. The female remains on -guard until the eggs are
hatched, of which she is apprized, it is said, by a peculiar noise
uttered by the partly imprisoned young. She thereupon reopens
the nest, and guides her liberated infants to the water, where she
leaves them to their fate. Whether this remarkable habit is one
that has been acquired in recent times or not is uncertain, but
because it has been observed in a number of unrelated forms, it is
probable that the instinct is of long inheritance, and may account
for certain peculiarities of structure in some of the ancient members
of the order. Doubtless the habit arose because of the unpro-
tected places in which the eggs are necessarily laid on the shores and
beaches, and because the eggs are comparatively so few in number.
The sea-turtles likewise lay their eggs in hollows scooped out of the
sand of the beaches, but the parents give no further care to their
eggs, nor to their newly hatched offspring, a neglect which is com-
pensated for by the much larger number of eggs they lay, because
of which the chances are much greater that a few will survive the
more numerous vicissitudes to which the eggs and young turtles

are exposed.
ANCIENT CROCODILES, MESOSUCHIA

The name Mesosuchia, meaning ‘middle crocodiles,’ by which
the ancient members of the Crocodilia have generally been known,
was given by Huxley in the belief that they were intermediate
between the “true” or modern crocodiles and an ancient group
which he united with the order under the name “‘Parasuchia.” A
fuller and better knowledge of the members of this last group has
proved very conclusively that they are really less allied to the croc-
odiles than are some other orders of reptiles, the dinosaurs for
instance, and should be properly classed by themselves as a distinct
CROCODILIA

order. And, more recently, it has
also become quite apparent that the
old crocodiles should not be separated
so widely from the modern ones as
Huxley proposed; that the differences
distinguishing them from the recent
members of the order are really not
of more than family importance. We
thus have left but two chief divisions
of the Crocodilia, the Eusuchia and
Thalattosuchia; and the latter group
even, bysome authors, perhaps rightly,
are included under the true crocodiles
as a family only.

These older crocodiles, the Meso-
suchia of Huxley, comprise a con-
siderable number of extinct forms
which lived as far back as the early
part of the Jurassic, and continued
nearly to, if not actually into, Ceno-
zoic time, that is, to the Eocene.
They differ from all living forms,
chiefly in having, not concavo-convex
but biconcave backbones, that is, the
more primitive vertebrae with which
all reptiles began. Nor was the inter-
nal opening of the nasal passages so
far back in the mouth as in the later
forms. In other respects they did
not differ very greatly from some of
those now living. All the earliest
kinds that we know of—the teleosaurs
—had a long, slender snout, resem-
bling very much that of the modern

gavials. And they were, for the most .

part, incased in a more complete bony
armor, on both the dorsal and the
ventral sides; and the front legs were

 

205

 

 

 

Fic. 106.—Teleosaurus; skull,
from above.
206 WATER REPTILES OF THE PAST AND PRESENT

smaller than those of the gavials even. The resemblance of the
living teleosaurs to the modern gavials must have been very
great, although the heavier bony armor indicates a less exclusively
aquatic lifé. They probably lived more in the shallow waters of
the seas near the shores.

Near the close of the Jurassic appeared for the first time, so
far as we now know, broad-headed mesosuchian crocodiles, forms
having less numerous and stronger teeth, and resembling closely
modern alligators. It has been believed that these broad-headed
kinds were of later origin than the more slender-nosed teleosaurs,
but a moment’s consideration will make it evident how improbable
such an evolution must be. The crocodiles must have descended
from strictly terrestrial reptiles, and no terrestrial reptiles have
a slender nose. That they should have acquired a slender face in
adaptation to water habits and then returned to the more primitive
land type with a broad face and less strictly aquatic habits is con-
trary to all our experience in paleontology. From this it is alto-
gether probable that broad-faced crocodiles of later times must
have been the descendants of broad-faced kinds that were in exist-
ence during all the Jurassic times, but of which we as yet have no
knowledge. These broad-faced Jurassic crocodiles were, for the
most part, small creatures, much smaller than the teleosaurs even,
and smaller than any species of crocodiles now living. Their
remains are known only from fresh-water or shore deposits, and are,
for the most part, associated with those of land and fresh-water
animals. About the time of their first known appearance in geo-
logical history, the small mammals and birds had also become more
or less abundant, and it was suggested by Owen that these land
animals had something to do with the development of the ancient
amphibious crocodiles. Perhaps this was the case with respect to
their greater abundance and development, and with certain pecu-
liarities of their structure, but that the gavial-like teleosaurs should
have come back to the land and reverted to a more primitive form
seems quite improbable.

During Cretaceous times, especially in America, numerous forms
of these old mesosuchian crocodiles were doubtless in existence, both
slender-nosed and broad-nosed, and some of them must have been
CROCODILIA 207

of considerable size, though none known was as large as some of
the late crocodiles. This type, with biconcave vertebrae, con-
tinued to live on, in both North and South America, to the latter
part of Cretaceous times, and it is even possible that some con-
tinued on into the Tertiary. But long before the close of the Cre-
taceous, the modern kind appeared, those with concavo-convex
vertebrae, and more posterior internal nostrils. The earliest are
known from New Jersey (Thoracosaurus, Holops), so like the Borneo
gavials of today that they are properly classified in the same family,
the Tomistomidae or Gavialidae. If all the later, procoelian type,
that is, those with concavo-convex vertebrae, originated from a
single form when the amphicoelian or mesosuchian type became
extinct, Huxley’s classification into the Mesosuchia and Eusuchia
would perhaps be proper, but we have much reason to suppose
that the change in the kinds of vertebra and in the position of
the nostrils was only incidental, and may have occurred in more
than one line of descent, that is, it may have occurred in the broad-
headed kinds of the Jurassic to the broad-headed crocodiles of today,
as also in the gavial-like forms of the Cretaceous to the gavials of
the present. And this is the reason why naturalists no longer
recognize the classification of Huxley, which, partly perhaps because
of the prestige of his name, has so long been accepted in our chief
works on natural history.

MARINE CROCODILES, THALATTOSUCHIA

While the ancient crocodiles of which we have spoken resembled
the modern ones so closely in form of body and probably in habits,
there were certain others of the old Jurassic seas which departed
so widely both in structure and in habits, from their associates that
they are by some authors given a place wholly by themselves
as a distinct group. This has been called by Professor Fraas *
the Thalattosuchia, a word meaning ‘‘sea-crocodiles.” They were
a very early side-branch from the great genealogical tree of the
Crocodilia, a branch which departed so widely from their asso-
ciates in adapting themselves to a peculiar and aberrant mode of
existence that they cannot be considered as typical crocodiles,
although so closely related to them in other respects that there
WATER REPTILES OF THE PAST AND PRESENT

208

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CROCODILIA 209

cannot be the least doubt regarding their ancestry. None of the
crocodiles which we have considered, whether ancient or modern,
can truthfully be called purely aquatic. They never ceased to use
their limbs for locomotion on land, more or less of the time, or for
the support of the body; and many of them have subsisted, in
part at least, on land animals. How easy it may have been for
some of them to become almost wholly emancipated from land
habits we may easily conjecture. The gavials, as we have seen,
are more at home in the water than upon land; their food is chiefly
found in the water; but, so long as their habits restrict them chiefly
to fresh water, or to the vicinity of the shores, their limbs continue
to be used as much for crawling as for swimming. Were the gavials
to be driven out to sea by the stress of fresh-water conditions or
attracted thereto by a greater abundance of more easily obtainable
or better food, so far from land that they no longer would have much
use for their legs for the support or propulsion of their bodies,
in the course of time they would doubtless change to.a more purely
aquatic type. And in that change there would be material modi-
fications of their structure: their limbs would become better
adapted to movements in the water; the skin would become
smoother, and the bony and horny scales would be lost, since they
would be not only useless in the water, but actually detrimental to
the well-being of the animals; and the tail would develop into a more
powerful organ of propulsion, as a means of increasing their speed
in obtaining food or in escaping their enemies, such as the sharks.
In fact, we can only imagine that in the transformation precisely
those modifications would occur which we actually find in these
old sea-crocodiles, the Thalattosuchia. And they are of especial
interest to us here because nowhere do we find a better example of
Nature in the act of transforming a terrestrial or subterrestrial
animal into a truly aquatic one.

The. group comprises only a few forms, so far as known. All
were of modest size among extinct reptiles, from ten to twenty feet
in length, and all are from the Upper Jurassic deposits of Europe.
They did not exist very long, probably because they found it im-
possible to discard old habits and old structures entirely and
become absolutely emancipated from the land; their breeding habits
210 WATER REPTILES OF THE PAST AND PRESENT

possibly were too deeply impressed into their structure readily to
change, as did those of other sea-reptiles. Some of their remark-
able aquatic adaptations have long been known, but only within
a dozen years has our knowledge of them become at all complete.
Three or four genera have been described, but only a few forms are
well known, of which Geosaurus may be taken as most typical.
To this we shall confine our descriptions.

The skull of Geosaurus is rather small in comparison with the
length of the body, smaller proportionally than in any living croc-
odile, but not much smaller than that of the teleosaurs. The
snout is long and slender, much like that of the teleosaurs and
gavials, but the bones of the whole upper surface are quite smooth,
not roughened and pitted like those of modern forms. The skull

 

Fic. 108.—Geosaurus; skull from side and from above. (After Fraas)

of Dakosaurus, another genus of thalattosuchians, is much less
elongate than that of Geosaurus, but has the other characteristics
of Geosaurus. ‘The eyes are provided with a stout ring of sclerotic
bones, with a pupillary opening of less than one inch. We have
seen that all other strictly aquatic reptiles have similar eye bones,
but no other crocodiles have them. The internal openings of the
nostrils are large and long, but they are not situated far back, as in
the modern crocodiles, not even so far back as in the early teleo-
saurs. They had no need of the peculiar breathing apparatus of
the amphibious crocodiles, since all their prey must have been
water-breathing creatures. Their eyes were directed laterally,
not more or less upward, as in their nearest relatives. Nearly all
other crocodiles have an opening through the hind end of the lower
CROCODILIA 211

jaw, but the thalattosuchians did not. The teeth were about as
numerous as in the modern gavials, but they projected freely only
a short distance above the gums in life, and they were very slender
and sharply pointed, excellently well adapted for catching smooth
and slippery fishes. Their vertebrae, like those of all other reptiles
of their time, were biconcave. Those of the neck resembled those
of the teleosaurs, save that there were only seven, fewer than is the
case with any other members of the order. In becoming adapted
to their peculiar mode of life these crocodiles lost two vertebrae
from the neck. All modern crocodiles have two ribs attached to the
first vertebra; the thalattosaurs had but one, another evidence of

 

Fic. 109.—Tail, scapula (sc), and coracoid (c) of Geosaurus. (After Fraas)

primitive characters. While the number of vertebrae in the neck
was reduced, in the back it was increased to eighteen; all other
crocodiles have but fifteen or sixteen. The trunk was long, another
adaptation to water life. There were two firmly united vertebrae
in the sacrum, as in the modern forms. The reason for the per-
sistence of this terrestrial character we shall see later.

The tail was very long and strong, nearly as long as all the
remainder of the body, and relatively much longer than in other
crocodiles. It is of interest to observe that the head, neck, body,
and tail had almost the same relative proportions as those of the
great sea-lizards, the mosasaurs. The terminal bones of the tail
212 WATER REPTILES OF THE PAST AND PRESENT

are very peculiar, and very different from the corresponding bones
of other crocodiles. While the spines of the tail bones along the
anterior part are only moderately stout and long, and are directed.
obliquely backward, near the
terminal part they become
suddenly much broader and
are directed upward, and, a
little farther along, obliquely
forward. The chevron bones
on the under side also here
become broader and longer.
The end of the tail curves
markedly downward to end
in a slender point. It will
be remembered that a similar
downward curvature of the
end of the -tail observed in
nearly all specimens of ich-
thyosaurs induced in Owen
the belief that the animals
had a fleshy terminal fin, a
belief which later discoveries
of the carbonized remains of
the flesh confirmed. The
peculiar structures observed
in various specimens of these
sea-crocodiles, even though
no impressions or remains of
the fleshy parts have been
discovered, is quite con-
clusive evidence that these
animals also had a broad,
fleshy, terminal fin. No other explanation of the structure is
possible.

The ribs are not at all stout and are not much curved. They
are directed posteriorly in the known specimens preserved in the

 

Fic. 110.—Geosaurus. Elongate hind leg,
and paddle-like front leg. (After Fraas.)
CROCODILIA 213

matrix in such a way as to indicate a slender thorax and
abdomen, not the broad body of the modern crocodiles. The
abdominal ribs, that is, those protecting the region on the
under side of the body between the breast bone and the pelvis,
are strongly developed in Geosaurus. The sternum, always present
in other crocodiles, is wanting in Geosawrus. The shoulder-
blades and coracoids, often changed in shape in water reptiles,
are not unlike those of the amphibious crocodiles, but are smaller
and flatter.

The fore limbs, to use Professor Fraas’s words, “‘are among the
most interesting of all the peculiarities of Geosaurus,” and show very
clearly that these animals were excellent swimmers. The humerus
is remarkably short and broad; the two bones of the forearm, the
radius and ulna, are broad, rounded, or angular plates, not long
bones, as in other crocodiles; the wrist bones also are broad and
plate-like. The three bones of the thumb, that is of the digit which
received most strongly the impact of the water in swimming, are
also broad and flat. All of these bones are marvelously aquatic in
type, as will be evident from a comparison of them with the cor-
responding bones Of the ichthyosaurs and mosasaurs. The bones
of the other fingers, however, were not much changed from the
ordinary crocodilian form, as a further comparison of them with the
fingers of a land crocodile will show. Furthermore the whole limb
or paddle was very small in comparison with the hind leg, and it was
attached very near to the head. The relative proportions of the
front and hind limbs in the geosaurs, gavials, and alligators are
instructive as showing the progressive decrease in size of the front
legs from the subaquatic, through the semiaquatic, to the almost
purely aquatic type. The hind legs, strangely enough, were not
very different in size and structure from those of the gavials or teleo-
saurs. The thigh bone is long and slender, though the bones of the
leg and ankle are somewhat shortened and flattened, as are also
those of the first toe. There were no claws on the hind feet, a
distinctly aquatic adaptation, and the toes were certainly webbed.
The pelvis, while not especially stout, is of good size, and was firmly
attached to the sacrum.
214 WATER REPTILES OF THE PAST AND PRESENT

Perhaps all these characters may best be summed up in the
words of Professor Fraas, as translated:

We recognize in Geosaurus an unusually slenderly built crocodile, in
appearance very different from all true crocodiles. The smooth, rounded
skull, with its greatly elongated and slender snout, and the deep-lying, small
eyes, reminds one most of the ichthyosaurs. The skull merges into the slender,
elongated trunk without a visible neck, and the body was provided neither
above nor below with horny or bony armor, but was, probably, as in the whales,
covered with a smooth, soft skin. The anterior extremities, attached far
forward, are developed as paddles, and served rather as organs of equilibration
than as a means of propulsion, which was the function of the elongated hind
legs and the extraordinarily strong and powerful tail, which supported at its
endalargefin. The entire impression given of the animal is that of an excellent
swimmer, with all the peculiar aquatic adaptations. In the skeleton, however,
all the characters of the original crocodiles are preserved. Most remarkable
are the laterally placed eyes, protected by the stout sclerotic bones, and the
overhanging bones of the orbits. So, too, the large temporal openings of the
skull, doubtless due to the absence of the bony plates in the integument, give
to the animal a strangely abnormal appearance for a crocodile.

We have observed that all the truly aquatic air-breathing ani-
mals, save the plesiosaurs, have either lost the hind legs or else
have them greatly reduced in size, and the disproportionately large
size of these members in Geosaurus seems inexplicable. But an
explanation is not, I think, hard to find. In the adaptation to
water life the first to become modified for the control of the body are
the front legs. The hind legs never have any really important use
when the tail is a powerful propeller. The hind legs of the geosaurs
are still essentially legs and not paddles, and they were doubtless
used either occasionally for propulsion on land, or perhaps for
pushing the body about on the bottom of shallow waters. And'the
presence of a well-developed ventral armor of bony ribs possibly
also indicates more or less of the terrestrial crawling habit. As
soon as the hind legs cease to be used for crawling they take on only :
a feeble use for the equilibration of the body, and speedily become
small, until finally they disappear. That the hind legs of these
creatures were of some use in the water is certain, because of the
modifications in their structure, and especially because of the loss
of the claws; but that they were of important use as propellers is
CROCODILIA 215

hardly probable. We may therefore infer that the thalattosu-
chians, while distinctively sea-reptiles, had not entirely lost their
land habits. Moreover, it is highly probable that their egg-laying
habits, which would hardly change with a greater adaptation to
water life, compelled the animals recurrently to visit the shores.
To have finally lost their hind legs they must have become vivip-
arous in habit, since it seems to be impossible for any true air-
breathers to be hatched in water. Perhaps this insurmountable
habit was the final cause of their extinction in competition with the
truly viviparous aquatic flesh-eaters. The thalattosuchians had
but a brief existence in geological history, during the latter part of
' the Jurassic period only, so far as certainly known, nor did they
become widely dispersed over the earth; they are known from
Europe, possibly from Brazil.
CHAPTER XVI
CHELONIA

No order of reptiles of the past or present is more sharply and
unequivocally distinguished from all others than the Chelonia
or Testudinata. No order has had a more uniformly continuous
and uneventful history. None now in existence has had a longer
known history, and of none is the origin more obscure. The first
known members of the order, in Triassic times, were turtles in all
respects, as well or nearly as well adapted for their peculiar mode
of life as are those now living, and were they now living they would
attract no especial attention from the ordinary observer and but
little from the naturalist.) From time to time some have gone
after better things, and have come to grief, but the main line has
remained with fewer improvements, fewer evolutional changes,
than any other group of higher “vertebrates. The turtles seem
very early to have adapted themselves so well to their peculiar
mode of life, to have intrenched themselves so thoroughly in their
own province, that no other creatures have been able to overcome
them, or to drive them from it. The remains of no other air-
breathing vertebrates are so omnipresent in the rocks as those of
the turtles; they may be expected wherever fossils of air-breathing
animals are found, though unfortunately often only in scattered
and broken fragments. The loose union of their skeletal bones
and their general habits of life in shallow waters left their bodies
as food for scavengers, or for dismemberment by the tides and
currents. :

Relationships with other reptiles they really have none. Some
have thought that the plesiosaurs were their first cousins, others
the Placodontia, an indeterminate group of extinct reptiles usually
placed with the Anomodontia. But their relationship with neither
of these is closer than with the crocodiles, dinosaurs, or ptero-
dactyls. They are the only reptiles that we know, besides the

216
CHELONIA 217.

cotylosaurs, which have no holes in the temporal roof of the skull,
and as the cotylosaurs were the most primitive and the oldest of
reptiles, this fact incontestably proves that the turtles had a very
ancient origin, though we know them no farther back than the
later Triassic. They are the only order of reptiles of which not
a single member is known to have teeth, or even vestiges of
them. Until recently only a single specimen has been known
from the Trias, and of that only the casts of the shell; but the
shell was as fully developed and as complete as that of a modern
alligator snapper, which it resembled much in form and in size.
And doubtless the habits of this ancient Proganochelys were similar
to those of the alligator snapper. The early cotylosaurian reptiles
were all littoral- or marsh-loving animals, and more or less aquatic,
and doubtless the early turtles continued in the same environments
and with the same habits after acquiring a shell for protection and
losing their teeth, which for some inexplicable reason they seemed
no longer to need. Until near the close of the Jurassic period
probably all turtles were amphibious animals of the marshes,
spending ‘much, perhaps the larger part, of the time in the water,
good swimmers, and yet good crawlers. With the beginning of
the Cretaceous, however, some of them became ambitious for new
and untried modes of life. Various ones went down into the sea
and became marine animals, reaching the zenith of their prosperity
and the maximum of size before the close of the period, but con-
tinuing in diminished size and numbers to the present time, if
we may consider the leather-back turtle as really their descendant.
Others in the Cretaceous took to the rivers and ponds, and became
almost as thoroughly aquatic in their thin shape and soft covering;
and their lineal descendants still continue in the rivers of the
Northern Hemisphere. Still others, in the Age of Mammals, took
to the upland, and competed with the mammals in the open places
and prairies, reaching their maximum in Miocene-Pliocene times,
when for some unknown reason the giants among them were driven
from the mainlands to continue a precarious existence to the present
time in some of the larger islands.

Were there no turtles living we should look upon the fossil
forms as among the strangest of all vertebrate animals—animals
218 WATER REPTILES OF THE PAST AND PRESENT

which had developed the strange habit of concealing themselves
inside of their ribs, for that is literally what the turtles do. The
box or shell of an ordinary turtle is composed of the backbones and
ribs, to which are soldered a shell of bony skin plates above, with
the clavicles, interclavicle, and ventral ribs below. Except in

 

 

Fic. 111 Fic. 112

Fics. 111 and 112.—Grapiemys. (From Hay)

Fic. 111.—Carapace: cpr, cp2, etc., costal plates; cs1, cs2, etc., costal scutes,
horny; 21, 2, etc., neural bones; up, nuchal bone; us, nuchal scute; py, pygal
bone; spy, suprapygal; spy 2, second suprapygal, or postneural; si, vs2, etc., verte-
bral scutes; 1, 2, 3-12 on right side, marginal scutes; 1, 2, 3-12 on left side, peripheral
bones. ‘

Fic. 112.—Plastron: ab, abdominal scutes; am, anal scutes; et, entoplastron
(interclavicle); epi, epiplastron (clavicle); fem, femoral scute; g, gular scute; hum,
humeral scute; /yo, hypoplastron bone; hypo, hypoplastron; im, inguinal scute;
py, pygal bone; xiph, xiphiplastron.

the strange leather-back turtle described farther on, these plates
form definite series. Ten of them cover the spines of the dorsal
vertebrae, in the midline, one over each, of which the turtles have
the smallest number of any known reptiles. There are eight on
each side over the ribs, united by suture with each other and with
the middle series; and, in addition, there are twenty-six bones
CHELONIA 219

surrounding them and attached to them. All these bones com-
pose what is called the carapace, which forms a complete roof in
the more terrestrial types, more or less imperfect, with vacuities
between the bones in the marine forms. On the under side, in
addition to the clavicles and the interclavicle, there are three
pairs of enlarged ventral ribs that go to form the plastron, solid
and complete in land turtles, with openings in the water forms.
And in the land forms
the plastron is more or
less firmly united with
the carapace.

In the skeleton con-
tained within the box
thus formed is the very
peculiar pectoral girdle,
composed of scapula
and coracoid, the scap-
ula so peculiar that
the controversy as to
its homologies is not
yet quite settled. Most
authors, until recently,
have believed that its peculiar shape (Fig. 113) is due to the
co-ossification of the procoracoid with the scapula instead of as
usual its loss or union with the true coracoid, so called. We are
now pretty sure that this is not true, since in reality there is no
such bone as the procoracoid, the bone so called being the real or
true coracoid; and because, in the second place, the long anterior
projection called the procoracoid is really only an outgrowth of the
scapula itself and not a fused, separate bone. Hence the bone is
properly called the scapula-proscapula, and not the scapula pro-
coracoid, as it usually has been. The coracoids are elongate and
flattened and without the usual supracoracoid foramen, so gener-
ally present in reptiles. The only other reptiles having a simi-
lar structure of the scapula are the plesiosaurs, and it has been
because of this apparent resemblance that some good paleontologists

 

Fic. 113.—Toxochelys; coracoid and scapula
220 WATER REPTILES OF THE PAST AND PRESENT

have thought the turtles and plesiosaurs were allied. The sacrum
is composed of two vertebrae only, and the pelvis of the usual
three bones, the ilium, the ischium, and the pubis, all covered over
by the shell.

In every known turtle the neck is composed invariably of eight
vertebrae, but they are peculiar in many respects. In the earliest
known turtles the neck vertebrae were, as would be supposed,
biconcave, but they soon became very variable in all; in each neck
some are biconcave, some
biconvex, some opisthocoe-
lous, and some procoelous.
And Dr. Hay tells us that
the neck has increased in
length in the later forms.

The skull also is very
peculiar in that it has
some very primitive char-
acters and others very
aberrant. The temporal
roof, as has been said, has
no holes through it, though
it is often reduced by the
emargination of the
borders, whether from be-
low or behind, until in
some the whole temporal

Fic. 114.—Pelvis of Chelone, from below: region is exposed, and not
pu, pubis: is, ischium; i, ilium (in acetabulum). at all covered over. There

is no parietal foramen, so
constantly present in all the early reptiles and in the lizards and
the tuatera of modern times. There are no teeth or vestiges of
teeth, but the jaws have usually a horny cutting edge, which seems
to be quite as serviceable; in the river turtle the lips are fleshy.
There is no transverse or transpalatine bone. There is a single
vomer only, not paired as in other reptiles, whence comes the
doubtful theory that the vomers of other reptiles are not the real
vomers originally so named in mammals, and hence often called

 
CHELONIA 221

prevomers. The vomer of the turtles under this theory is believed
to be the real homologue of the mammalian bone. The palate is
always slightly, sometimes nearly wholly, underfloored, as in mam-
mals, carrying the internal nostrils far back in the mouth. In the
occipital region of the skull there is a separate bone on each side
called the paroccipital or opisthotic, which has been indistinguish-
ably fused with the exoccipital in all other reptiles except the ich-
thyosaurs since Triassic times.

   

Fic. 115

Fies. 115 and '116.—Trachemys. (From Hay)

Frc. 115.—Skull from above: jr, frontal; ju, jugal; pa, parietal; paoc, paroc-
cipital; pfr, prefrontal; pof, postfrontal; pro, prodtic; gu, quadrate; sq, squamosal;
_$oc, supraoccipital.

Fic. 116.—Skull from below: av, alveolar surface of maxilla; boc, basioccipital;
bap, basisphenoid; exoc, exoccipital; mx, maxilla; pal, palatine; paoc, paroccipital;
pmx, premazilla; pro, prodtic; pt, pterygoid; qu, quadrate; gj, quadratojugal;
5g, squamosal; vom, vomer.

In the feet the numbers of phalanges—that is, the bones of the
free digits—are like those of mammals, that is, two in the first
cand three in each of the other four digits. The land tortoises have
lost some of these, while the river turtles have either gained one
or two in the fourth finger and fourth toe, or else have enjoyed
an uninterrupted descent from the primitive reptiles which normally
222 WATER REPTILES OF THE PAST AND PRESENT

possessed that number. All other reptiles, save those phylogeneti-
cally allied to the primitive mammals, that is, the Theriodontia
and their allies, have normally the phalangeal formula 2, 3, 4, 5, 4.
It was partly because of this similarity of the numbers of toe bones
that the turtles have been classed in the great group of reptiles
that includes the ancestors of the mammals; that is, under this
theory, the turtles would enjoy a nearer relationship to the mam-
mals and to man himself than any other living reptiles! But this
classification has been shown to be quite artificial.

 

Fic. 117.—Limbs of Colpochelys, a recent sea-turtle: H, humerus; R, radius;
U, ulna; 7, radiale; z, intermedium; w, ulnare; 4, pisiform; c, centrale; T, tibia;
F, fibula; a, astragalus; m, fifth metatarsal. (From Wieland.)

From what has been said, it will be surmised that the Chelonia
represent in themselves one of the primary subdivisions of the class
Reptilia, and that, unlike most others, the order has enjoyed a most
remarkable longevity. And doubtless they are one of the primary
branches of the reptilian stock, which has remained distinct since
Permian times at least, if not since Carboniferous, isolated and
remarkably homogeneous, giving off no branches which departed
far from the main stock, and on the whole leading a singularly
placid existence for ten or more million years.

In most textbooks the order Chelonia is divided into three
suborders, the Pleurodira, the Cryptodira, and the Trionychoidea.
CHELONIA 223

In recent years, however, the earlier members of the older group
of Pleurodira have been separated into a fourth suborder, the
Amphichelydia, a group characterized by some not very impor-
tant differences in the plastron and skull, and including those
forms in which the cervical vertebrae are amphicoelous. This
group continued to Eocene times before it became extinct, and
consisted of archaic forms which persisted after all the other sub-
orders had come into existence. The Cryptodira, especially char-
acterized by the manner in which they withdraw the head and neck
within the shell by an §-like vertical flexure, are known from the
Lower Jurassic and are still the dominant group of today, with more
than one hundred and forty living species. The Pleurodira in the
narrower sense are first known from their remains in the Upper
Cretaceous of North America and are still represented by about
forty species, living in the Southern Hemisphere. They are dis-
tinguished from the other groups by the manner in which they with-
draw the neck and head into the shell, by a horizontal, sidewise
flexure. The third suborder, the Trionychoidea, also began in
Cretaceous times, so far as we know, and are represented by about
seventy living species, chiefly in the Northern Hemisphere. They
are especially characterized by the absence of bony marginal
plates and the soft epidermis.

With the exception of the land erie all turtles from the
beginning of their career as an order to the present time have been
more or less at home in the water. In some, like the marine forms,
the adaptation to aquatic life has produced marked changes in
structure: in the loss of the horny dermal shields and in the loss
of bone tissue; in the flattening of the shell, and in the development
of the front legs into swimming flippers, with.a loss of the claws.
In the absence of a guiding tail, which is always small in the marine
turtles, propulsion must of course be wholly by the aid of the limbs.
As oar propellers the marine turtles show some of the peculiar
characters of the plesiosaurs. With a like short and broad body,
a more or less elongated and flexible neck, there could be no sinuos-
ity of the body in swimming. As an oar-like organ the humerus
became flattened, and its muscular attachments, as in the plesio-
saurs, descended far down the shaft, giving greater mechanical
224 WATER REPTILES OF THE PAST AND PRESENT

advantage. Unlike all other aquatic vertebrates, the turtles never
developed real hyperphalangy. Only in the river turtles is there a
possibility of an increase in the bones of the fourth digit.

To discuss in general the structure and habits of the living
chelonians would extend this chapter to an undue length, and would
add nothing to the many excellent works on natural history
accessible to the student. We have therefore contented ourselves
with a brief outline of the geological history of the order, with
especial reference to their aquatic habits.

SIDE-NECKED TURTLES. PLEURODIRA

The suborder of Chelonia, generally known as the snake-necked
or side-necked turtles or tortoises, comprises about forty living spe-
cies, confined to South America, Africa save the northernmost part,
Madagascar, New Guinea, and Australia. In Australia they are
the only members of the order known—another instance of the
peculiar isolation of the fauna of that region. In the past they
lived in North America during Upper Cretaceous times, the earliest
known forms of the group in its restricted sense, of which seven
species are described by Hay. In Eocene times they are also
known from Europe and Asia, from both of which regions they have
long since disappeared.

The Pleurodira, as the term indicates, are easily distinguished
from all other turtles by the way in which they withdraw the head
within the shell. Instead of withdrawing it by an S-shaped flexure
of the neck between the shoulder-blades, as do other turtles, these
bend the neck laterally in a horizontal plane, bringing the head
within the margins of the shell in front of one or the other foreleg;
and the margins of the shell are produced here in an eave-like
fashion for the greater protection of the head. In the structure of
the shell, which is always fully developed into a box, these turtles
do not differ very much from the Cryptodira, though there may be
some extra bones in the plastron, as also in the skull. The nasal
bones are always, the lacrimals sometimes, well developed; the latter
never, the former rarely, found in other groups. The lower jaws
articulate a little differently, and the external ear is always fully
surrounded by bone. Very characteristic is the bony union of the
CHELONIA 225

pelvis with the plastron below, which never occurs in other turtles,
unless it be the Amphichelydia.

The side-necked turtles are all of fresh-water habit, similar to
that of the fresh-water tortoises spoken of farther on. The neck
is often very long and snake-like, which accounts for one of the
names given to these turtles; because it is withdrawn into the
shell sidewise, it has more distinctively ball-and-socket joints
between the vertebrae, with distinct transverse processes for the
attachment of the necessary side-moving muscles. The feet in all
are more or less webbed and armed with strong claws.

The largest and perhaps the best known of all living side-
necked turtles is the giant Amazon turtle of South America, which
sometimes has a shell nearly three feet in length. Its feet are
broadly webbed, and the shell is rather flat in the adult; it is an
excellent swimmer in the waters of the Orinoco and Amazon. Six
or seven species of the genus to which it belongs are known, all
of them South American except one that lives in Madagascar
and one fossil found in the Eocene of India. This remarkable
distribution is but one more of the many instances known in
zodlogy and paleontology that seem to prove an early land con-
nection between India and South America. Had the migration
between the two continents occurred by way of Asia and Bering
straits, as did that of hosts of mammals, one would certainly expect
to find some evidence of it in the North American Tertiary rocks,
which, so far, is lacking.

CRYPTODIRA

The chief families of the Cryptodira turtles are the Chelydridae,
or snappers; the Emydidae, or marsh tortoises; the Testudinidae,
or land tortoises; the Chelonidae, or sea-turtles; the Protostegidae,
or ancient sea-turtles; and the Dermochelydidae, or leather-backs.
Other doubtful or smaller groups, both living and extinct, may be
omitted, or incidentally mentioned. .

SNAPPING TURTLES

The family of snapping turtles, the Chelydridae, are of interest
because of their peculiar geographical distribution at the present
226 WATER REPTILES OF THE PAST AND PRESENT

time. Only four species are known, three of them from North
America, the fourth from New Guinea. ‘The family is one of the
most primitive of living turtles, though no members of it are known
with certainty from earlier rocks than the Oligocene. In all prob-
ability, also, they have retained, more than have any other group
of turtles, unless it be some of the fresh-water tortoises, the primi-
tive habits of the earlier or earliest turtles, though of course there
have been modifications, both in structure and in habits. The
three species of the United States include two of the snapping
turtles proper and: the alligator turtles of the southern states,
which sometimes reach a length of three feet. All the species are
largely aquatic in habit, powerful and active swimmers, with
webbed feet and strong claws, and both on the land and in the
water they are bold and fierce. They have a relatively large head
and very strong jaws. Agassiz saw one bite off a piece of a plank
an inch in thickness, and they can usually be raised from the ground
by any object which they seize. The carapace and plastron are
much reduced, and are rather loosely united. The shell is not
large enough for the complete withdrawal of the head and legs
within it, and the tail is unusually large and strong. The common
snapping turtle, Chelydra ser pentina, is found from Canada to Ecua-
dor, and its remains have been found with those of the mammoth
and mastodon in Pleistocene deposits; and related species of the
same genus have been reported from the Miocene of England.

FRESH-WATER OR MARSH TORTOISES

The family of turtles or tortoises (Emydidae) represented at
the present time by the common terrapin, painted tortoise, and
box tortoise of the United States, and commonly called fresh-
water turtles or tortoises, comprises the largest group of living
chelonians—nearly a third of all existing members of the order.
They are widely distributed over all parts of the earth except
Australia, and are of very varied habits. Some are almost exclu-
sively aquatic; others, like the painted tortoise, are partially so-
while others, especially the common box tortoise, are almost as
exclusively terrestrial as the true land tortoises, dying even, if
forced to live long in water.
CHELONIA 227

The shell in the more aquatic forms is depressed or flattened,
but in the terrestrial kinds may be as highly arched as in the true
land tortoises. The feet are adapted primarily for walking, but
nearly always have the toes webbed, and the digits are longer
than are those of the land tortoises. Only the'two or three middle
toes have claws. Some species have developed hinges in the plas-
tron, whereby they may be completely closed up after the head
and legs are withdrawn within the shell. Most of the species are
carnivorous in habit, but a few, like the box tortoise, are strictly
vegetarian.

Geologically the fresh-water tortoises have a not very ancient
history, going back no farther than do the land tortoises, that is,
to the beginning of the Cenozoic or Age of Mammals. Fully
fifty species are known from the Tertiary rocks of North America,
or more than three-fourths as many as are now living upon the
earth.

The family at most can be said to be only amphibious in habit,
and has no striking aquatic adaptations, since the shell is well
developed and is covered with horny shields. The flattened shell
of the more aquatic forms is characteristic, as is also the greater
degree of webbing between the toes.

LAND TORTOISES

Perhaps the last of the more noteworthy specializations of the
Chelonia, and indeed among the last of the more important speciali-
zations of the Reptilia, are the upland tortoises, of which the com-
mon ‘‘gopher”’ of the southern states is almost the only remnant
in North America. They formed a part of the great hegira of
forest and marsh animals to the open prairies, away from the low-
lands and water which the turtles had inhabited almost exclu-
sively for millions of years.

They began their career, Dr. Hay thinks, at about the begin-
ning of the Cenozoic, that is, with the great development of the
mammals, and reached the maximum of their development in the
Miocene; and they have been on the decline ever since. In the
Northern Hemisphere, at least, the slowly cooling climate through-
out the Eocene, and a decided decrease in moisture, brought about
228 WATER REPTILES OF THE PAST AND PRESENT

the prairies and prairie plants before its close. Just as the horses,
rhinoceroses, camels, and other herbivorous mammals took to these
open places for the better and more abundant food found therein,
so also the lowland tortoises found better food and fewer enemies
there, for they are all strictly herbivorous in habit. The mammals
became more conspicuous to their enemies when they went into
the open, and it was only by the development of speed, more sober
coloration, and perhaps greater cunning that they found safety
from them. The tortoises were handicapped by low intelligence,
and they could not develop speed, for they were not constructed to

        

Es Zs 7
ae WD) Pn
EG ACY

Fic. 118.—Testudo sumeirei, a giant upland tortoise. (From Hay, after Roth-
schild.)

that end. But they did find protection in their bony shell, which
became thicker, higher, and more convex, and with smaller open-
ings. To quote Dr. Hay: ‘‘We may suppose that it would be
much more difficult for a carnivorous animal to effect an entrance
into such a shell than into one depressed, and whose borders may
be spanned by the jaws of their enemies.” Perhaps also the highly
arched form of the shell gave greater capacity for the lungs, and
the tortoises in general, it is said, do have better lung capacity
than the more aquatic or lowland types of turtles. Possibly, also,
the heavier shell lessened the evaporation of the body fluids, and
made the tortoises less dependent upon the vicinity of water.
CHELONIA 229

Certain it'is that the common box tortoise, of like form and habits,
occurs not rarely on the arid plains, far from water. ;

The neck and legs became fully retractile within the shell;
the digits were shortened up, without a vestige of webbing mem-
brane between them; the phalanges were reduced in number to two
in each toe, and nearly all the toes have well-formed claws. The
feet are placed squarely upon the ground, and the body is elevated
in walking. They can swim, when by accident they are thrown
into the water, only as any terrestrial mammal can.

About forty species of land tortoises are known throughout
the world at the present time, though North America, the probable
original home of the tribe, has but three, all small. The larger
species are all now denizens of islands, especially the Galapagos
Islands, where the giant tortoises have long been famous. And
many of our living forms have changed but little since Eocene
times. In the Oligocene and Miocene they inhabited western
North America in enormous numbers. In the Bad Lands of South
Dakota one can often see the remains of a dozen or more of these
giant tortoises at one time, specimens varying from one to three
feet in length of shell. In river deposits, those of the late Miocene
or early Pliocene, the writer has seen areas of an acre or more
literally strewn with their remains, as though droves of them had
been overwhelmed and perished together. About fifty species of
these land tortoises are known from the American Tertiary, thirty-
two of them belonging to the modern genus Testudo, which com-
prises the giant tortoises of the Galapagos. The largest known
species of the group is one of Testudo from the Pliocene of India,
which had a shell six feet in length. Why the larger species became
extinct in Pliocene times on the mainland to survive only in the
islands is not known; possibly their carnivorous enemies became
too cunning and too numerous.

SEA-TURTLES. CHELONIDAE

The sea-turtles, or Chelonidae comprise five or six living species,
inhabitants for the most part of tropical and subtropical oceans,
of which the green or edible turtle (Chelone), the hawksbill turtle
230 WATER REPTILES OF THE PAST AND PRESENT

(Caretta), and the loggerhead (Eretmochelys [Fig. 119]) are the best
known. They are all thoroughly aquatic in habit, and of large
size, from three to five feet in length. The carapace is heart-
shaped, and reduced, that is, with large openings between the
ribs; the plastron also is reduced and loosely united to the carapace.
The neck is short and the head is not retractile within the shell.
The temporal region of the skull is roofed over. The four legs
form large and powerful flippers, and the hind legs are relatively
small. The body is flattened and the tail is small. The aquatic

 

 

 

 

Fic. 119.—Eretmochelys, loggerhead turtle. (By permission of the New York
Zodlogical Society.)

characters of the limbs are seen especially in the broad and strong
humerus, with the radial crest for the attachment of powerful
muscles situated far down on the shaft; in the relative shortness
of the radius and ulna, and the large size of the latter bone; in the
flattened carpal bones; and in the great elongation of the digits
and the absence of all but one or two of the claws. Unlike the
leather-back turtle and the Cretaceous sea-turtles, the carapace
and plastron are completely covered with horny shields, from which
indeed the tortoise shell of commerce is derived. Except the green
turtle, all members of the family are carnivorous.
CHELONIA 231

Extinct members of the family are known from scanty remains
in Cenozoic and late Cretaceous rocks. From the earlier Cretaceous
deposits of the plains more primitive allied forms occur, often
classed in distinct families of which Toxwochelys (Fig. 120) and
Desmatochelys are the more noteworthy. The latter genus, espe-
cially, might well have
been an ancestor of all
the modern forms.
About three feet in
length, it had all the
essential characteristics
of the sea-turtles, in its
thin form, roofed-over
skull, reduced carapace,
loose plastron, and
flipper-like limbs. The
single known speci-
men, preserved in the
museum of the Uni-
versity of Kansas, came
from the lower rocks of
the Upper Cretaceous

of Nebraska. Yet

earlier, at the close of Fic. 120.—Carapace of Toxochelys bauri, an
; Upper Cretaceous sea-turtle: ep, epineural. (After

Wieland.)

 

 

 

 

 

the Jurassic, there were
shore turtles of con-
siderable size that had begun to develop a fondness for the open
seas; to acquire a depressed form and lightened shell, the limbs
still retaining, however, more of the terrestrial or crawling form.
They are grouped as a separate family, the Thalassemydae, and
include the first of the Chelonia to depart from the marsh and
fresh-water habits which for long ages, perhaps, had limited the
activities and evolution of the turtles.

ANCIENT SEA-TURTLES. PROTOSTEGIDAE

Forty-four years ago the late Professor E. D. Cope, one of the
greatest naturalists America has ever produced, in almost the
232 WATER REPTILES OF THE PAST AND PRESENT

earliest exploration of the great Cretaceous fossil deposits of western
Kansas, discovered and collected a remarkable specimen of one

 

Fic. 121.—Toxochelys latiremis; front leg: hum, humerus; rad, radius; ul, ulna;
int, intermedium; win, ulnare; , pisiform; cen, centrale. (From Wieland.)

 

Fic. 122.—Desmatochelys lowii: skull from above and below

of the most extraordinary turtles that is known even yet. By an
error somewhat natural for those times, when the theory of evolu-
tion was just beginning to attain acceptance by naturalists, he
CHELONIA 233

thought that the specimen, notwithstanding its monstrous size,
represented a very primitive kind of turtle, and gave to it the name
Protostega gigas, meaning gigantic first roof! The late Professor
George Baur, to whom paleontology owes so much, showed that,
far from being a primitive turtle, Protostega was really one of
the most specialized types of the order. Professor Cope’s account
of the discovery of the specimen is of so much interest that it
may be quoted here:

“In the very young tortoise or turtle the ribs are separate, as
in other animals. As they grow older they begin to expand at the
upper side of the upper end, and with increased age the expansion
extends throughout the length. The ribs first come in contact
where the process commences, and in the land tortoise they are
united at the end. In the sea-turtles the union ceases a little
above the ends. The fragments of the Protostega were seen by
one of the men projecting from a ledge of a low bluff. After
several square feet of rock had been removed, we cleared up the
floor and found ourselves well repaid. Many long, slender pieces
of two inches in width lay upon the ledge. They were evidently
ribs, with the usual heads, but behind each head was a plate like
the flattened bowl of a huge spoon, placed crosswise. Beneath
these stretched two broad plates, two feet in width, and no thicker
than binder’s board. The edges were fingered and the surface
was hard and smooth. All this was quite new, among fully grown
animals. Some bones of a large paddle were recognized, and a
leg bone. The shoulder-blade of a huge tortoise came next, and
further examination showed that we had stumbled on the burial
place of the largest species of sea-turtle yet known. But the ribs
were those of an ordinary turtle just hatched, and the great plates
represented the bony deposit in the skin, which, commencing
independently in modern turtles, unite with each other at an early
day. But it was incredible that the largest of known turtles should
be but just hatched, and for this and other reasons it has been con-
cluded that this ‘ancient mariner’ is one of those forms, not un-
common in old days, whose incompleteness in some respects points
to the truth of the belief that animals have assumed their modern
perfection by a process of growth from more simple beginnings.”
234 WATER REPTILES OF THE PAST AND PRESENT

Later studies by Doctors G. Baur, E. C. Case, O. P. Hay, and
especially G. R. Wieland, of the abundant and excellent material,
preserved in the museums of Yale and Kansas universities and
the Carnegie Institution, and especially the discovery by Wieland
in 1895 of an allied and yet larger form which he called Archelon,
have determined practically every detail of the structure of this
remarkable group of sea-turtles. A surprisingly complete speci-
men of Archelon is mounted in the museum of Yale University.

 

Fic. 123.—Archelon ischyros; skeleton from above: n, nuchal, r, 7,7, ribs; m, m,
peripheral bones; /, humerus; r, radius; 7, ulna; #, tibia; fi, fibula. (From Wieland.)

About a half-dozen species and two genera of the family have
so far been described, all coming from the Upper Cretaceous
deposit of Kansas and South Dakota, the genus Archelon from later
rocks than those which have yielded Protostega.

The general form and structure of Archelon will best be under-
stood from the accompanying figures after Wieland (Figs. 123,
124, 125) and the restoration of the living animal as interpreted
by the writer (Fig. 126). If the leather-back turtle, described
CHELONIA 235

farther on, is really the descendant of these or allied turtles, as many
authors believe, it of course represents the very highest aquatic
specialization of all Chelonians. If, on the other hand, as some
believe, the leather-back is the end of a long and independent line
of descent, then Archelon represents the highest aquatic specializa-
tion of all other turtles.

In size, at least, Archelon attained the maximum of the order,
reaching a length of more than twelve feet, and a weight of more

 

Fic. 124.—Archelon from below, without plastron: 4, humerus; r, radius; u, ulna;
sc, scapula; c, coracoid; #, pubis; 7, ischium. (From Wieland.)

than three tons. Except that the shell was not heart-shaped or
elongated as in all modern sea-turtles, but nearly circular in out-
line, it had all the aquatic adaptations of the sea-turtle in a yet
higher degree.

The shell was depressed; the dermal plates covering the ribs
had almost entirely disappeared, remnants only of their upper
ends remaining; the skull (Fig. 127) had the temporal region
wholly roofed over; the neck was short and not retractile. The
236 WATER REPTILES OF THE PAST AND PRESENT

front legs were strong flippers, the humerus was long and stout,
with the crest for the attachment of muscles far down on the
shaft; the digits were greatly elongated and clawless, etc. The
plastron only was less reduced than in the case of the modern sea-
turtles. No traces of horny shields have been discovered. As to
the nature of the covering and the general appearance of the

 

Fic. 125.—Archelon; skeleton from below: hy, hyoplastron; pp, hypoplastron.
(From Wieland.)

turtle when alive, Dr. Wieland has kindly given the writer his
views, as follows:

“After direct study or fairly close examination of all the fossil
material of importance thus far collected representing the Pro-
tostegidae, it seems certain that in all the members of the group
an external leathery layer was well developed. In no instance is
there the slightest trace of horny shield sulci, or grooves; though
it seems probable that there was some gradation toward a thin and
perhaps even slightly horny hide. In Archelon ischyros the re-
duced condition of the carapace and the presence of the continuous
CHELONIA

eJOYVC YIMNOG jo snoaoeyaig siaddy ay} wor apinj-eas oUeBIB v ‘soukyose UO[aYIAP.

 

“QzI “OLY

 

 

 
238 WATER REPTILES OF THE PAST AND PRESENT

row of largt, median, supraneural elements render it quite certain
that there was a development of leathery hide comparable to
that of Dermochelys. The same may be said of Protostega gigas.
But Archelon Marshit had aless reduced carapace, and the leathery
skin was probably less well developed; and Protostega Copei, in
which no trace of supraneurals remains, must have made some
approach to the horn-shield condition. A more distinct suggestion
of transition from the leathery to the horny shield covering may be
seen in the very different contemporary Cretaceous form, Toxo-
chelys Bauri, where ossified epi- or supraneurals occupy quite

 

Fic. 127.—Skull of Archelon ischyros: pa, parietal; f, frontal; pm, premaxilla;
pf, prefrontal; pif, postfrontal; m, maxilla, 7, jugal; gj, quadratojugal; sur, surangu-
lar; d, dentary; am, angular. (After Wieland.)

exactly the nodal relation of the five vertebral horn shields of later
turtles, like Lytoloma, though there are not the slightest traces of
sulci.

“From a purely anatomical standpoint I have suggested that
Archelon had seven dorsal keels corresponding to those of Dermo-
chelys. There is much excellent reason for regarding dermogene
ossification as essentially double-layered throughout the Reptilia.

“Tn any restoration of Archelon ischyros only the mid-line should
be accentuated as a series of rather sharp supraneural crests. These
are shown to have been present by the characteristic groove-like
median pits with radiating striae, which are such a prominent
feature of epineurals. It is reasonable to believe that the pits
mark the attachment of horny crests developed in the leathery
hide. Such were doubtless projected, more or less keel-like, to
CHELONIA 239

a height of one or two inches, and thus gave to the mid-line of the
carapace, when seen laterally, a distinctly sinuous outline not
unlike that of Toxochelys.”

As regards the habits of these ancient sea-turtles, we may offer
tolerably certain conjectures. In the opinion of the writer, the less
reduced plastron indicates a bottom-feeding habit, a view that is.
strengthened by the more rounded form of the shell, like that
of the river turtle. All in all it would seem that Protostega and
Archelon lived habitually on the soft bottoms of the shallower seas,
feeding upon the hordes of large shell-fish, for which their powerful
parrot-like beak was admirably adapted. That the species of Proto-
stega did not commonly frequent the deeper oceans is indicated by
the general absence of their remains in‘the deeper water deposits.
The writer, in a long collecting experience, always found their
remains associated with those of the smaller Toxochelys, toothed
birds, pterodactyls, and the smaller mosasaurs.

Perhaps no one can speak more authoritatively as to the habits
of these gigantic sea-turtles of the Cretaceous than Dr. Wieland:

“With regard to the general habits and appearance of Archelon
much might doubtless be said if the present-day sea-turtles were
more familiar objects. Dr. Hay thought that Archelon ischyros
was a clumsy or even a sluggish, mainly littoral animal, moving
slowly about the bottom of quiet inlets in quest of shell-fish; I, on
the contrary, much struck by the powerful flippers, and especially
by the flattening of the humerus, with its low radial crest and obvi-
ously strong musculature, have held that unusual swimming power
and adaptation to a strictly marine life were indicated. Perhaps,
as usual where experts differ, it is probable that both views are in
part correct, and that Archelon was only a moderately good swim-
mer. It may be noted that, notwithstanding the almost circular
body, the femoral notch, that for the hind leg, lies far back, so that it
is not necessary, on the score of bulk, to assume slowness of motion,
or the inability to pursue a sea-going life. Furthermore, it is now
known that the development of the digits fell little short of that
seen in Colpochelys (Fig. 117) or Eretmochelys, truly marine turtles.

“Therefore, while there can be no doubt that Archelon was
strictly carnivorous in habit, and well able to navigate the open
240 WATER REPTILES OF THE PAST AND PRESENT

seas, it is not likely that it fed on other than relatively slow-moving
prey. Lydekker looked upon the broad mandibles and broad
palate of Lytoloma as specializations for a mussel diet; and very
similarly in Archelon, while the decurved beak would easily trans-
form him into a most formidable enemy, the heavy premaxillaries
and vomer, and the flat but deep lower jaw, suggest an adept
crusher of crustaceans. The presence of vast quantities of Nautilus
dekayi, which I found accompanying one of the specimens, was
doubtless accidental, but it plainly suggests that this cephalopod
was one of the teeming sources of food in the Archelon environ-
ment.

“The huge bulk of the mature Archelon might account for the
shearing off and loss of the flippers of younger forms caught between
the shells of the ‘elder boatmen of the Cretaceous seas,’ as Cope
has called them, during any sudden rush while herding on the shores.
But probably the young turtles did not much frequent the shores
at either egg-laying or other times. Whence it is much more likely
that it was a mosasaur or some of the gigantic fishes like Portheus
which bit off the right hind flipper in the type specimen of Archelon
ischyros, well above the heel, as I have described it. That this
happened rather early in life is shown by the arrested growth of
the right femur and remaining portions of the tibia and fibula,
which are all uniformly 1o per cent smaller than the corresponding
bones of the left flipper.”

While there were many small fishes in the Niobrara seas which
the Protostegas inhabited, the most striking thing in the fauna is
the great abundance of molluscal shells, especially Ostrea congesta.
And with them were great hordes of larger pelycypod mollusks,
some of them of enormous size. Some of the largest reach a
diameter of nearly four feet, with shells so thin that one can hardly
understand how they could have supported such large, oyster-like
creatures. One can imagine that such shell-fish might have afforded
an almost inexhaustible source of food for the large turtles; and
several times the writer has found remains of Protostega associated
with such shells. From all of which evidence it seems very prob-
able indeed that Dr. Wieland is right in imputing to these gigantic
turtles a shell-feeding habit, a habit which required neither speed
CHELONIA 241

nor great prowess; and perhaps the formidable beak was used more
in social quarrels than for food-getting. That these marine turtles
departed from the usual reptilian habit of laying their eggs upon
land is improbable. The tortoise shell turtles of the Bahamas lay
three or four hundred eggs in a hollow scooped out in the sand and
then leave the young to their own devices; certainly many a
one is gobbled up by birds of prey or other enemies on their way
to the water. Perhaps the young Archelon lost its hind leg in
some such mishap.

LEATHER-BACK MARINE TURTLES

The most remarkable member of the Chelonia now living is
Dermochelys coriacea (Fig. 128), the great leathery or leather-back
turtle of the warmer parts of the Atlantic, Indian, and Pacific
oceans, the sole member of the family Dermochelydidae. It is
the largest of all living turtles and the most thoroughly aquatic
of all, whether living or extinct. It sometimes reaches a length
of six feet, or half that of the largest known extinct forms, and
weighs a thousand ot more pounds. Agassiz saw a specimen that
he said weighed aton. Unlike other turtles, it has a carapace quite
peculiar to itself, composed of a layer of thin, irregularly polyg-
onal bones forming a mosaic, completely hidden in the thick skin, -
and entirely free from the skeletal bones beneath them. The
larger of these skin bones form seven rows above, which appear
in the living animal as sharp keels running the whole length of
the shell. On the under side there are five rows of smaller-sized
bones, under which there are vestiges of bones representing the
normal plastron of turtles. The limbs are powerful, flattened
paddles, not unlike those of Eretmochelys, but wholly destitute of
claws. The front paddles are much larger than the hind ones;
the humerus is long and flattened, and the digits are elongated.
The leather-back is a powerful and effective swimmer, going long
distances. Its habits are not well known; its food is chiefly fish,
crustaceans, and mollusks.

So very different is the structure of its shell that some excellent
naturalists regard Dermochelys as the equivalent in rank of all other
turtles combined, the sole representative of the suborder Athecae,
242 WATER REPTILES OF THE PAST AND PRESENT

as distinguished from the Thecophora. Dr. Hay, whose authority
on fossil turtles is of the highest, believes that its line of ancestry has
been distinct from that of all other turtles from Triassic times at
least. Others believe that the leather-back is merely a highly
specialized form derived from the ordinary shelled type, a de-
scendant of some of the marine turtles of Cretaceous times. In

 

 

Fic. 128.—Dermochelys coriacea. (From Brehm)

support of the primitive ancestry of the leather-back Dr. Hay
offers the following:

“The writer holds the view that the earliest turtles possessed
practically two kinds of shell, one purely dermal, consisting prob-
ably of a mosaic of small bones arranged in at least twelve longi-
tudinal zones. Each zone probably consisted of a row of larger
bones bordered on each side by smaller bones. Each of these bones
was covered by a horny scute. The nearest approach to such a
dermal shell is in our days seen in Dermochelys. Beneath the skin
there seems to have existed a carapace more or less complete, which
consisted of a nuchal, a median row of neurals, eight pairs of costals,
CHELONIA : 243

a pygal, probably one or more supraneurals, and about eleven
peripherals on each side. To what extent the neurals and the
costal plates had become anchylosed to the neural spines and the
ribs respectively, it is now impossible to determine. Nor can we
say to what extent the various elements of the carapace had become
connected with one another. There was a subdermal plastron
which was composed of at least eleven bones.

“According to the author’s view, as time went on the external,
mosaic-like shell disappeared in most turtles, while a more efficient
armor was developed out of the subdermal elements. In the ances-
tors of Dermochelys, however, the dermal armor was retained, while
the more deeply seated one disappeared, with the exception of the
nuchal bone.”

Such a hypothesis as the foregoing satisfactorily explains the
extraordinary mosaic shell of the léather-back, and is perhaps an
acceptable explanation of the rather strange fact that the horny
shields of turtles do not correspond with the bones below them,
as might be expected. Unfortunately this hypothesis lacks
sufficient proof. About the only evidence ‘that is offered in its
support is the existence of a row of bones along the middle line in
the Cretaceous Toxochelys, and notably in Archelon, both aquatic
forms. It is urged that these bones, the epineurals of Wieland,
are really the remains of an external layer that persisted in these
turtles. However, they might have been new ossifications, such
as we know did occur in not a few of the land tortoises later over the
tail and limbs. Aside from Proganochelys in the vast interval of
time from the Triassic to the Eocene no other evidence of such
an external dermal layer has been discovered. The chief argument
against such divergent ancestry of the turtles in two chief lines of
descent is the fact that in its other structure Dermochelys shows
great resemblance to other sea-turtles of the Cretaceous times—
so much resemblance that it seems impossible that the ancestors of
the leather-back should have paralleled them in almost everything
except the shell.

On the other hand, those who disagree with this view believe
that the modern leather-back is the descendant of such Cretaceous
marine turtles as Protostega or Archelon, some of which had lost
244 WATER REPTILES OF THE PAST AND PRESENT

nearly all of the costal plates and had the neurals and marginals
reduced. It is urged that some of these early marine forms, after
they had practically lost the ordinary bones of the carapace, for
some reason or other found a bony shell again necessary for their
welfare. Possibly they had become littoral in habit; possibly they
again became subject to new and dangerous enemies in their
unprotected condition, notwithstanding their great size; perhaps
the zeuglodons were among their enemies. Now, as we have seen,
an animal never takes a back track and recovers a thing it has
once lost. It was impossible for the ancestors of the leather-back
again to acquire an orthodox shell, and they forthwith proceeded to
acquire quite another kind that would serve the same purpose.

Possibly the truth lies between the variant views, in the theory
recently expressed by Versluys: ‘‘The shell of tortoises and turtles
is formed by a combination of two layers of dermal ossifications, a
thecal layer and a more superficial epithecal layer, the latter
generally represented by the. marginals only. The leather-back
is a member of the Cryptodira, and is allied to the other marine
turtles. The problem of the origin of the aberrant shell of the
leather-back seems to find its solution in the hypothesis that it is
a secondary proliferation of the marginals and such other epithecal
elements as were present in its thecophorous ancestors.” |

In other words, Versluys believes that Hay’s and Wieland’s
views of the primitive double layer of exoskeletal bones is essentially
correct, but that Dermochelys was derived from later forms in which
some of them, only, as in Avchelon, had remained. Baur’s conten-
tion that ‘““Dermochelys is not the least, but the most specialized
marine turtle’? seems to have been fully justified.

RIVER TURTLES. TRIONYCHOIDEA

No reptile is more familiar or more exasperating to the river
fisherman than the turtle, variously known as the river, soft-
shelled, or mud turtle. It lives, often in great numbers, in most
of the rivers, ponds, and bayous of the interior east of the Rocky
Mountains, and especially in those of sluggish current and muddy
bottoms. It is voraciously carnivorous in habit, feeding upon the
smaller fish, mussels, and such other living food as it can capture.
With its long, sinuous neck and snake-like head, and soft, mottled
CHELONIA 245

skin, it is repulsive enough to most persons, but is especially annoying
to the fisherman, since it devours with impunity his bait so long
as he feeds it, and can seldom be caught on the hook because
of its hard and bony mouth, in which only by good luck will the
hook catch. And the luckless string of fish that the fisherman
leaves in the water may be almost completely devoured in a few
hours by these fiercely predaceous feeders. However, if so annoy-

 

 

Fic. 129.—Trionyx, river turtle. (By permission of the New York Zodlogical
Society.)

ing while seeking for better game, it in part makes up for the
annoyance it causes by furnishing in its own body a not unpalatable
food for those who like to eat reptiles.

The river turtles will be readily recognized from the accompany-
ing illustration (Fig. 129). They are very flat, covered with a
soft, smooth skin, with a long, sinuous neck and a small, snake-like
and vicious-looking head which has a protuberant snout with the
external nasal orifice at its end. Their feet are webbed and some-
what paddle-like, but always with three stout claws—whence
246 WATER REPTILES OF THE PAST AND PRESENT

comes the name of the group—on the anterior digits, which are
used for burrowing in the mud and excavating holes for their
eggs. These turtles burrow more or less in the mud, with the long
neck free, lying in wait for their prey, and coming to the surface
from time to time to breathe. As the shape of the body and the.
paddle-like feet would suggest, they are active swimmers and purely
aquatic in habit, never leaving the water unless compelled to.
They bury their hard-shelled eggs on the shores only a few feet
from the water, and leave them to their
fate. If the pools in which they live dry
up, they burrow deeply in the mud and
await the rains and floods. In captivity
they feed upon all kinds of food, vegetable
as well as animal, and are active and
aggressive.
Because of certain peculiarities, they
ij 4 are usually classed in a separate suborder
:& all their own, the Trionychoidea, especially
\ distinguished from the Cryptodira, which
in general they resemble in most respects,
aside from the absence of the usual horny
dermal plates, in the lack of a marginal
row of bony plates around the carapace
—not a very important distinction. Less

 

Fic. 130.—Aspideretes, a
trionychoid turtle from than thirty living species are known, all

the Basal Eocene of New of them exclusively or chiefly of fresh-

Mexico; skull from above.

(cen Haas water habit. Six species are known from

North America; the remainder inhabit
Africa, south of the Sahara Desert, southern India, and most of
the East Indian islands; none is known from Australia. No
species lives in South America and none is known to have lived
there in past times. During Eocene, Oligocene, and Miocene times
these fresh-water turtles lived in the region of Europe in great
numbers, but for some inexplicable reason they became extinct
there and never returned. Nearly seventy species of the Triony-
choidea, belonging in two families, are described by Dr. Hay from
the Tertiary rocks of North America, more than twice the number
CHELONIA 247

now living throughout the world. Some of these were of relatively
large size, measuring fully two feet in the length of the shell.
And in some places they must have been very
abundant. The writer has seen, in the Bad
Lands of the Continental Divide, their
weathered-out remains so numerous that they
might be raked into windrows miles in length
along the sloping bluffs, all in small frag-
ments, for their bones, like those of most
turtles, are only loosely united by sutures
and readily drop apart before fossilization.
Their shells may be readily distinguished
from those of all other turtles by the granu-
lated, pitted, or sculptured exterior surface,
that was covered by the skin in life; other
turtles have the surface smooth below the
horny shields, the margins of which are
marked on the bones by grooves or sulci;
the few marine turtles of the past that were
probably covered with a soft skin instead of
horny shields had the shell smooth and much
less completely ossified.

As to the origin of the soft-shelled turtles
there has been not a little difference of
opinion. The earliest ones known in geo-
logical history date back only to about the
middle of the Cretaceous; perhaps they
branched off from the horny-shelled turtles
somewhat earlier, but probably not much.
There are some, however, who think that = pyg. 131 — Aspidere-
this group of turtles was very primitive, per- es, a trionychoid turtle
haps the most primitive, but the writer agrees from the Eocene of

. Z ee nae : New Mexico; front leg.
with Dr. Hay in rejecting this view. Unlike ror Hay
those of all other turtles, the fourth digit in
front and hind feet has one or two more phalanges than have other
turtles. We have seen that the oldest known reptiles had the
digital formula 2, 3, 4, 5,3 0r4. Most other turtles have the same

 
248 WATER REPTILES OF THE PAST AND PRESENT

numbers of bones in the digits that mammals have, that is, two
phalanges in the thumb and big toe and three in each of the other
digits. The river turtles have a larger number in the fourth digit,
either four or five. It seems to be a law that evolution is irre-
versible, and if so could the river turtles have been descended from.
forms with a less number of phalanges? But, the skeleton of the
Trionychoidea resembles the more specialized turtles in so many
ways that one can hardly believe they were all accidental or parallel.
We may then assume that at about the time that the ordinary
marsh turtles took to the sea to become marine, others took ad-
vantage of the fresh-water ponds and rivers, and in doing so, like
the marine turtles, lost their horny epidermal shields, and became
thinner in shape, thereby reducing the resistance to the water.
Instead, however, of reducing the costal plates over the ribs, they
retained them intact and complete for some reason or other, but
‘lost instead the marginal row of bones, unlike the marine turtles
which retained them even after they had lost nearly all of the costal
plates. Possibly also they regained additional bones in the fourth
digit, a sort of hyperphalangy like that of the more strictly aquatic
reptiles. Or, possibly, they may have descended from some branch
_of the turtles which had not yet lost these bones, retaining them
because they were still serviceable for swimming. We know
nothing yet about the structure of the feet of the early turtles, and
it is possible that not all had acquired the reduced phalangeal
formula.

In the development of aquatic habits the river turtles do not
show the same degree of specialization in the limbs that the strictly
marine forms do. The humerus (Fig. 131) is a slender bone, with
the tuberosities for the attachment of the muscles situated near
the proximal end. The radius and ulna are relatively short, and
the foot is long. The hind legs, as would be supposed, are less
highly-specialized as swimming paddles, and are relatively smaller.
Nevertheless the Trionychoidea present an interesting type of
adaptation to water habits, both in body and in limbs.
INDEX

Adaptation to aquatic life, 59.
Aetosauria, 187.

Aigialosaurs, 146.

Alligator, 142, 197.
Amblyrhynchus, 142.
Andrews, C. W., 75.
Angistorhinus, 190.
Anomodontia, 102.

Aquatic reptiles, adaptation of, 59.
' Araeoscelis, 133, 138.
Archelon, 234, 236, 238, 239.
Archosauria, 33.

Aspiderectes, 246, 247.

Baptanodon, 113, 114, 1177
Baur, George, 119, 120, 185, 234.
Belodon, 185, 189, rgr.
Belodontia, 185.

Béche, De la, 73.

Bogalobou, 75.

Broom, Robert, 5, 102, 103, 129.
Brown, Barnum, 93, 179.
Buckland, Dean, 75, 77.

Cacops, 35.

Camper, Adrian, 149, 166.

Camper, Peter, 149, 166.

Captorhinus, 49.

Caretta, 230.

Carpus, 38.

Casea, 55.

Case, E. C., 234.

Champsosaurus, 79, 180, 181, 182.

Chelone, 220, 229.

Chevrons, 32.

Choristodera, 178.

Classification of reptiles, 13.

Clavicles, 37.

Cleithrum, 36.

Clidastes, 147, 154, 155, 157, 166.

Collection of fossils, 10.

Colpochelys, 222.

Conybeare, Rev., 73, 110, 149.

Cope, E. D., 126, 176, 178, 185, 231, 233.

Coracoid, 36.

Cotylosauria, 16.

Cryptodira, 226.

Cretaceous of Kansas, 8.

Crocodiles, ancient, 204;
modern, 195.

Crocodilia, 15, 194.

Crocodilus, 195. :

Cuvier, Georges, 73, 97, 107; 110, 149.

marine, 207;

Darwin, Charles, 142.

De Fond, St. Faujas, 148.
Dermochelys, 241, 242.
Desmatochelys, 231, 232.
Dimetrodon, 36, 51.
Dinosauria, 18.
Dolichosaurs, 145.
Dolichobrachium, 54.
‘Dollo, Louis, 167, 179.

Edaphosaurus, 22.

Elasmosaurus, 78, 84, 86, gr.
Enaliosauria, 75. ’

Eosauravus, 52.

Episcoposaurus, 190.

Eretmochelys, 230.

Eryops, 31, 47.

Eusuchia, 195.

Exoskeleton, 43.

Extinct reptiles of North America, 52.

Femur, 41.

Fibula, 41.

Foot, 42.

Fraas, Eberhard, 74, 75,99, 111, 115, 185,
213.

Gastroliths, 92, 200.

Gavial, Borneo, 201; Gangetic, 198, r99
202.

Gavialidae, 203.

Geological Ages, 46.

Geosaurus, 208, 210, 211, 212, 214.

Gervais, Professor, 126.

Gilmore, Charles, 113, 167.

Globidens, 167.

Goldfuss, August, 151.

Graptemys, 278.

Hadrosaurus, 56.

Hand, 38.

Hauff, B., 122.

Hay, Oliver P., 220, 227, 228, 234, 242.
Hofmann, Dr. 148.

Holops, 207.

Home, Everard, 110.

Homo diluvii testis, 108.
Huene, Friedrich von, 131, 185.
Humerus, 38.

Huxley, Thomas, 185, 207.
Hydrus, 169.

Hyperphalangy, 118.
Hypocentrum, 36.

249
250

Ichthyosauria, 17, 107.
Ichthyosaurus, 108, 112, 119, 121, 122.
Iguana, r4o.

Tlium, 39.

Interclavicle, 37.

Intercentrum, 30.

Ischium, 39.

Jaeger, George, 184.
Jaekel, 185.

Karoo beds, 102.
Koenig, 110.

Labidosaurus, 22, 26, 50.

Laecertilia, 140.

Lariosaurus, 99, Tao.

Leather-back turtles, 241.

Leidy, Joseph, 151.

Limnoscelis, 20, 47.

reo 140; flatheaded, 144; Galapheoa,

Lull, "Richard, 54.
Lystrosaurus, 103, 104.
Lortet, M., 135.

McGregor, J. H., 126, 129, 131, 185, 186,

189.

Mandible, 25.

Mantell, Dr., 75.

Marsh, O. C., 54, 185.

Merriam, J. C., 112, 120, 171, 174.

Merriamia, 778.

Mesosaurus, 126, 127, 128.

Mesosuchia, 185, 204.

Meyer, Herman von, 75, 87, 132, 134, 184.

Mixosaurus, 119.

Monitor lizards, 144.

Mosasauria, 148, 166.

Mosasaurus, 148; hofmanni, 149; maxi-
miliani, 151.

Miinster, Georg von, 97.

Mudge, B. F., 93.

Mystriosuchus, 185, 188, 189, ror.

Nares, 23.

Nectosaurus, 175.
Nothosauria, 95.
Nothosaurus, 96, 97, 98.

O’Fallen, Major, 151.

Ophiacodon, 30, 32, 37, 38, 40, 42.
Ophidia, 168.

Ophthalmosaurus, 178, 125.

Orders of reptiles, 16.

Osborn, H. F., 126.

Ostodolepis, 33.

Owen, Richard, 75, 103, 110, 111, 185.

Paleorhinus, 190.
Paliguana, 5.

WATER REPTILES OF THE PAST AND PRESENT

Parasuchia, 18, 184.
Parietal foramen, 23.
Pectoral girdle, 34.

Pelvic girdle, 39.

Pelvis, 39.

Petycosauria, 186.
Pelycosimia, 187. -
Phytosauria, 18, 187.
Phytosaurus, 186, 187.
Pineal foramen, 23.
Platecarpus, 151, 155, 156, 158, 159, 166.
Platynota, 148.
Plesiosauria, 77.
Plesiosaurus, 74.
Pleurodira, 224.
Pleurosaurus. 134, 136, 177.
Polycotylus, 80.

Proatlas, 32.
Proganochelys, 217.
Proganosauria, 17.
Proteosaurus, I10.
Protorosauria, 17, 132.
Protorosaurus, 132.
Protostega, 233, 234.
Protostegidae, 231.
Pseudosuchia, 185.
Pterosauria, 18.

Pubis, 39.

Pythonomorpha (Mosasauria), 166.

Range of Reptilia, 45.
Rhachitomous vertebrae, 17.
Rhynchocephalia, 17, 176.
Rhytidodon, 190.

Ribs, 33.

River turtles, 244.
Rutiodon, 190.

Sacrum, 32.

Sapheosaurus, 178.
Sauranodon (Baptanodon), 125.
Sauropterygia, 17, 73.
Scheuchzer, 107

Seeley, H. G., 75, 126, 132.
Seymouria, 27, 48.
Shoulder girdle, 34.
Simoedosaurus, 179.
Skeleton of reptiles, 19.
Skull of reptiles, 21.
Snakes, 168.

Spener, 132.

Sphenodon, 24, 132, 176.
Squamata, 17, 138.
Stegocephalia, 48.
Stereosternum, 126.
Sternum, 37.

Stomach stones, 200.

Tarsus, 42.
Teeth, 21, 25.
INDEX

Teleosaurus, 205.

Temporal openings, 23.

Testudo, 228.

Thalattosauria, 17, 171.

Thalattosaurus, 172, 173, 174.

Thalattosuchia, 207.

Therapsida, 16.

Theromorpha, 16.

Thaumatosaurus, 74.

Thoracosaurus, 207.

Tibia, 41.

Tomistomidae, 201.

Tortoises, 216; fresh-water, 226; land,
227; marsh, 226.

Toxochelys, 219, 231, 232.

Trachemys, 221.

Trimerorhachis, 25.

Trinacromerum, 77, 81, 83, 85, 88, 89.

251

Trionychoidea, 244.

Trionyx, 245.

Tuatera, 176. See Sphenodon.

Turtles, 216; river, 244; sea, 229; ancient
sea, 231; side-necked, 224. ,

Tylosaurus, 153, 155, 157, 160, 165, 166.

Varanus, 144.

Varanops, 53.

Ventral ribs, 34.

Vertebrae, 28; notochordal, 29; rbachi-
tomous, 31.

Versluys, 244.

Watson, D. M. S., 103.

Wieland, G. R., 234, 236, 239, 243.
Woodward, A. S., 126.

Zittel, Carl von, 185.