Samuel Wendell Williston.

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WATER REPTILES OF THE PAST
AND PRESENT



THE UNIVEESITY OF CHICAGO PRESS
CHICAGO, ILLINOIS



Agrttts
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



3) 6




I



THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS



Copyright 1914 by
The University of Chicago



All Rights Reserved



Published October 191 4



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
earlier 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.



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 PAGE

I. Introduction . . i

II. Classification of Reptiles 13

III. The Skeleton of Reptiles . . . . . . . -19

IV. The Age of Reptiles 44

V. Adaptation of Land Reptiles to Life in the Water . . 59

VI. Order Sauropterygia . . . 73

Plesiosauria.
Nothosauria.

VII. Order Anomodontia .102

Lystrosaurus.

VIII. Order Ichthyosauria 107

IX. Order Proganosauria 126

Mesosaurus.

X. Order Protorosauria 132

Protorosaurus.
Pleurosaurus.

XL Order Squamata 138

Lizards.

Mosasaurs.
Snakes.

XII. Order Thalattosauria 171

XIII. Order Rhynchocephalia 176

Choristodera.

XIV. Order Parasuchia 184

Phytosauria.
XV. Order Crocodilia 194

Eusuchia.

Mesosuchia.

Thalattosuchia.

XVI. Order Chelonia 216

Side-necked Turtles.
Snapping Turtles.
Fresh-water or Marsh Tortoises.
Land Tortoises.
Sea-Turtles.
Ancient Sea-Turtles.
Leather-back Marine Turtles.
River Turtles.

vii



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,



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 zoologists 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 are 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



s



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




Fig. i. — 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 g

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


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Online LibrarySamuel Wendell WillistonWater reptiles of the past and present → online text (page 1 of 19)