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MERICAN

NATURAL HISTORY

The American Museum of Natural History is devoted to exploration, research and education in the natural sciences for the purpose of en- couraging and developing an understanding of nature for the advance-

ment of all mankind.

The Dinosaur Book

By Edwin H. Colbert

Curator of Fossil Reptiles and Amphibians

The American Museum of Natural History

Pam StiiAt ED BY JOHN CC. CERMANN

With additional illustrations, previously published,

by Charles R. Knight and others

PUBLISHED FOR

BY

McGRAW-HILL BOOK COMPANY, INC.

NEW YORK LONDON TORONTO

THE DINOSAUR BOOK

Copyright, 1945, 1951, by The American Museum of Natural History. All rights

in this book are reserved. It may not be used for dramatic, motion-, or talking-

picture purposes without written authorization from the holder of these rights. Nor may

the book or parts thereof be reproduced in any manner whatsoever without permis-

sion in writing, except in the case of brief quotations embodied in critical articles and

reviews. For information, address the McGraw-Hill Book Company, Inc., Trade De- partment, 330 West 42d Street, New York 18, New York.

SECOND EDITION

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Published by the McGraw-Hill Book Company, Inc.

Printed in the United States of America

LO WILLIAM KING GREGORY

TEACHER, AUTHORITY ON FOSSIL AMPHIBIANS AND REPTILES, AND PROFOUND STUDENT OF VERTEBRATE EVOLUTION

Preface

HERE HAS BEEN considerable progress in

the study of fossil amphibians and rep-

tiles since The Dinosaur Book was first printed. However, in order to make this second edition available without a long and costly delay it was felt wisest to keep correc- tions and revisions on this new issue down to those which reflected the major recent advances. It is hoped that this new edition of the book will be useful to those who are interested in a broad outline of amphibian and reptilian evolution.

For many years there has been felt the need for a popular guide book on the fossil amphibians and_ reptiles, with particular attention given to the dinosaurs. Dinosaurs, by W. D. Matthew, published by the Ameri- can Museum of Natural History in 1915, has long been out of print.

This book has been prepared to fill a definite need, namely, to tell the story of amphibian and reptilian evolution. The book is written to supplement the displays of fossil amphibians and reptiles in the American Museum of Natural History, but the subject matter is handled in such a way that it may be used by anyone interested in the subject, whether he has access to our Museum halls or not. Therefore it is written in general terms, and references to particu- lar skeletons or fossils on exhibit are omit- ted. To the museum visitor, the label will identify the display. Moreover, the animals described in this book are illustrated by

restorations showing their appearance in life, rather than by photographs of skeletons on exhibit. To the museum visitor the actual fossils are at hand, so it is super- Huous to repeat them with pictures in a book such as this. To all readers, whether they have access to the Museum or not, it is felt that restorations give a more graphic picture and convey more information than do skeletons, the bones of which are un- familiar to most people. Therefore much at- tention has been given to the restorations used. All of the new restorations have been made by Mr. John C. Germann, while, in addition, certain of the well-known restora- tions by Mr. Charles R. Knight have been repeated. They are worthy of constant repe- tition, for no better impressions of some of the former denizens of our land have ever been created.

Several people have aided the author in bringing this book to successful completion. Special acknowledgments are due to Pro- fessor William King Gregory of Columbia University and the American Museum of Natural History, to Professor Alfred S. Romer of Harvard University, and to Mr. Charles M. Bogert of the American Museum of Natural History. These eminent authori- ties were all kind enough to read the manu- script and to offer criticisms and sugges- tions.

Epwin H. CoLsert

Contents

PREFACE ib

1. INTRODUCING THE DINOSAURS ial

2. PIONEER STUDENTS OF THE DINOSAURS 15 List of North American museums housing collections of fossil

reptiles and amphibians 23

38. Huntinc DINosAuRS 25

4. THe AGE OF REPTILES 36

5. Tue First LANp ANIMALS 4]

6. PRimitiIvE REPTILES ‘ 47

7. THE MAMMAL-LIKE REPTILES 53

8. ANCESTORS OF THE DINOSAURS 60

\9. THe Kinps or DINosAuRs 64

Saurischia 68

Ornithischia ii

/10. ADAPTATIONS OF THE DINOSAURS 84

11. DrnosaurIAN ASSOCIATIONS 94

{ 12. Fuicur 97

Pterosauria 97

The Birds 100

113. SEA SERPENTS 104

The Ichthyosaurs 105

The Euryapsida 110

The Mosasaurs 112

The Marine Crocodiles 114

14.

)15.

' 16. 17.

18.

1)

DECLINE OF THE DINOSAURS

THE SURVIVORS Crocodiles, Ancient and Modern The Long-Persistent Rhynchocephalians The Lizards and Snakes The Turtles

Wuy Strupy Fossiis? WHERE THE DINOSAURS AND THEIR RELATIVES ARE FOUND

How THE DINOSAURS AND THEIR RELATIVES ARE CLASSIFIED AND NAMED Synoptic Table of the Amphibia and Reptilia, Including the Genera Mentioned in This Book

OTHER SOURCES OF INFORMATION

INDEX

time, long ages ago, there were dino-

Be _ saurs on the earth. Indeed, the pub-

PL

lic has become “dinosaur-conscious’—so much so, that the word “dinosaur” has be- come a common term in the English lan- guage, a word that stands for strength, size, and antiquity.

And it is no wonder that the average man has at least a slight nodding acquain- tance with the dinosaurs, for in these days of widely disseminated thought they are all

Introducing the Dinosaurs

around him. Fossil skeletons are to be seen in the exhibition halls of many of our larger museums. Here also are pictures showing what these ancient animals looked like when they were alive. And from the mu- seums they get into books of various kinds.

Now and then a dinosaur will show up on the Broadway stage or at a World’s Fair. They are constantly popping out at us in humorous cartoons, and they frequently come to life in the movies. Their remains and the tracks they made can be seen

11

in various localities throughout North America; one famous dinosaur collecting ground has been made a National Monu- ment just so that visitors can see how dinosaurs are discovered and excavated from the ground. Modern man, whether he wants to or not, is sooner or later going to run into a dinosaur or something having to do with dinosaurs.

Reproduced by special permission from The Saturday Evening Post.

Copyright 1939 by the Curtis Publishing Company Not in the way that the cave men are

“Te. nha, ’ : Demet FY R : > It’s hard to believe we’re made like that inside! sometimes portrayed as meeting ihe dimo-

ery saurs, with club or spear. No cave man a : ever saw a dinosaur. No human being ever met one alive, for the dinosaurs disappeared from the face of the earth millions of years before the first men appeared. Yet this idea of man and the dinosaurs living together at one time does persist, and it illustrates one

of many misconceptions that are common with regard to the dinosaurs. Indeed, so persistent is this idea that

_ Noni oS ee, = Reproduced by special permission of The Saturday Evening Post. Copyright 1940 by the Curtis Publishing Company

“T don’t mind you boosting your home state, Conroy, but stop telling the children that dinosaur is a California jack rabbit!”

Leonard Dove, in Collier’s Weekly “We had seven hundred natives excavating the ruins, but you'll never guess who found it.”

Copyrighted. Reprinted permission The New Yorker “And here is my first dinosaur—makes me feel like a kid again every time I look at it.”

there are periodic outbreaks of sensational stories having to do with dinosaurs that are still living in some far corner of the South American jungles. Sir A. Conan Doyle’s romantic novel The Lost World was based upon this idea. And no matter how often this misconception is killed by scientific facts, it keeps coming to life.

Another misconception is the common one that dinosaurs were all tremendously large beasts, crashing through the strange forests of an ancient world and tearing up trees by the roots. It is true that many of the dinosaurs were large, and some of them were the greatest animals ever to walk across the land, but it is equally true that there were many medium-size and small dinosaurs.

What, then, are the facts about dino- saurs? How did they live? What did they eat? How did they reproduce? What kinds

Copyrighted. Reprinted permission The New Yorker “Take a telegram to the Museum of Natural History.”

DINOSAURS IN THE PUBLIC EYE wey

By Henry Boltinoff in Maclean’s

2 ; “Homer told me before we were married he was a paleontologist. “Adds a little life to the old place, don’t you think?” But I didn’t know what it was!”

William Hayes in Collier’s Weekly

RT SL I AEB IE ra

13

of enemies did they have, and how did they succeed in ruling the earth for so many millions of years? This seems like a lot to ask about animals that no one ever saw alive, yet the answers to these questions have been pretty well worked out through the scientific detective work that has brought us to our present rather complete knowledge as to the anatomy, the habits, and the environment of the dinosaurs. They are oft-repeated questions, too, for the subject of dinosaurs is a fascinating one to a very great many people.

Let us therefore get acquainted with the dinosaurs in a proper way, let us learn to know them instead of continuing to look at them from across the street.

The dinosaurs were reptiles, cold-blooded animals related to the crocodiles, lizards, and snakes. They lived during the Mesozoic period of Earth History, which began some 200 million years ago and ended about 60

It is the purpose of this book to present a picture of the various kinds of dinosaurs, to explain their relationships to one another and to other reptiles, to inquire into the manner in which they lived together, and to explore the environmental conditions that surrounded them and: determined the separate courses of their varied life his- tories. Since there were other reptiles living with the dinosaurs, the picture cannot be thoroughly understood unless it is com- pletely presented, so these contempo- raneous animals will also be described, and their places in the general scheme of life will be evaluated. Finally, since the dino- saurs came from earlier reptilian ancestors, the primitive reptiles of earlier ages will be discussed, while the ancient amphibians, the ancestors of all four-footed animals will also be considered. In short, this will be a story of the evolution of vertebrate life on the land_as it occurred between the

million years ago, at which time the dino- emergence of the first land living animals, saurs became extinct. The dinosaurs were e amphibians, from their fish ancestors,

of many kinds, some being of tremendous some 340 million years ago, to the fina

size, some small, some adapted to a car- nivorous or meat-eating mode of life, some OES E105 ee Ie. Large or small, meat-eating or plant-eating, the dinosaurs were dinosaurs by virtue of their anatomical structure—a subject that will be explained in more detail at another place in this book. They were the ruling land_animals of Mesozoic times, and _con-

sidering the great duration of the stage in Earth History through which they lived,

they must be considered as among the most

successful of the backboned animals.

4

culmination and the ultimate decline of reptilian dominance, almost 300 million years later.

It is a story of great proportions, stretch- ing over long periods of Earth History. It is a story on so vast a scale as to dwarf our own history almost to insignificance. Yet great as are its dimensions, it is a story that is finished, for it is a tale of the triumph of brawn, a triumph that was long-lived, but which in the end gave way to the triumph of brain. The dinosaurs had their day, and while it lasted it was a Great Day.

Z

Pioneer Students of the Dinosaurs

HUNDRED YEARS OR SO AGO the science

of paleontology was in its infancy.

There were no well-established tech- niques for the discovery and excavation of fossils, and the study of ancient life on the earth was carried on in a rather haphazard manner. Fossils were to a great extent the result of accidental finds. Some quarrymen would turn up a strange object while work- ing out roofing slates or building blocks or road material; this strange object would be regarded with a suspicious eye, argued about, and finally presented to the nearest available “professor” for identification. Per- haps the professor would not be able to place it, in which case he would pass it along to another professor until finally the fossil, usually a pitifully small fragment, would come to rest in the collection, or the “cabinet” (as museums were then called), of some college or university or learned so- ciety. Fossil collections were largely the re- sult of chance, and the study of fossils was therefore for the most part opportunistic. Naturally, the existing knowledge of past life on the earth was very spotty and in- complete.

Since knowledge of past life was incom- plete, its interpretation was inadequate. But as men became more and more inter- ested in the history of the earth they be- came more aware of the fact that the chance collection of fossils and their chance study would hardly suffice to give a true understanding of the development of an- cient life. Consequently the subject began to attract serious students, who based their work on materials avowedly collected for study—not upon the chance discoveries of

quarrymen. Thus began the pioneer period in the science of paleontology, the period when the study of fossils became a well- founded full-time subject of investigation by serious, trained scholars, rather than an avocation for gentlemen of broad interests.

The outstanding figure of the pioneer period was Baron Georges Cuvier, the great French anatomist and paleontologist. Cuvier (1769-1832) became interested in Natural History at an early age, and by the beginning of the nineteenth century he was established as Professor of Natural History at the Collége de France. From about 1798 until the time of his death he applied him- self diligently to the study of fossil verte- brates (backboned animals), publishing many important papers and memoirs on the comparative anatomy and the classification of the vertebrates—both living and fossil. As a result of his labors the inter- relationships of the backboned animals and the unity of their basic pattern were for the first time adequately elucidated to the scientific world. He may be said to have been the founder of the science of Vertebrate Paleontology.

A contemporary of the great Cuvier was Dr. Gideon Mantell (1790-1852), an Eng- lish physician, who during the early part of his life lived at Lewes, south of London. Doctor Mantell became interested in fossils to such an extent that he turned with vigor to the excavation and study of extinct animal life as it was preserved in the Wealden or lower Cretaceous sediments around Lewes. He justly attained eminence as a student of geology and paleontology through the important discoveries that he

15

1g . Engraved by C. E. Wagstaff

The great Swedish botanist Linnaeus (1707- 1778) originated the system that is still used for naming and classifying all plants and animals

4

Georges Cuvier (1769-1832) won lasting fame by revealing the relationships among backboned animals, particularly as shown by their skeletons

Richard Owen (1804-1892), outstanding authority of his time, coined the name Dino- sauria and established the study of extinct animals on a scientific basis in England

16

Charles Darwin (1809-1895) revolutionized scientific thought throughout the entire field of natural history and ranks as one of the world’s greatest students of Life

made and the lucid papers that he pub- lished, describing and interpreting his finds. Perhaps Mantell’s chief claim to fame was his discovery and description of Iguanodon, the first dinosaur to be found in England. Indeed, his_paper-on _Iguanedon, published in 1825, established Mantell as the pioneer student of the dinosaurs in

In Lewes the house of Gideon Mantell is still standing, and on a brass plate fastened outside the door of this house are these words:

“He discovered the Iguanodon”

However, the greatest of the early Eng- Tish students of dinosaurs and other extinct

animals was Sir Richard Owen (1804-1892). If Cuvier may be called the founder of the

science of vertebrate paleontology, Owen may be called the man who established the science in England. Like so many early students of Natural History, Owen pre- pared himself for the practice of medicine, but by the time he had completed his medical studies it became apparent to his professors that he was much too valuable a man to go into general practice. So he turned to anatomical research and in due course of time became Hunterian Professor at the Royal College of Surgeons. However Owen's interests ranged far beyond the field of human anatomy, and he became by virtue of his investigations the outstanding authority of his time on the anatomy of the backboned animals, both living and extinct. He was the first Director of the Natural History division of the British Museum, and was instrumental in establishing this institution in its present buildings in the South Kensington district of London. Many of Owen’s studies were on dino- saurs. It was he who first recognized that

these extinct reptiles needed a name to designate them, and it was he who coined the word Dinosauria. Subsequently Owen’s name became anglicized to dinosaur, and today it has acquired an established place in our common language.

Strange as it may seem, one of the first excavators of fossil reptiles (although the objects dug up were not dinosaurs) was not a learned student of paleontology but a young girl.

Mary Anning lived at Lyme Regis in southern England with her father, in the early days of the last century. In those days many people from London sought the fresh airs of the seacoast, and Richard Anning made a small living by collecting fossil sea- shells and selling them to the tourists. In this interesting trade he was aided by his daughter, Mary, who may be said to have been an early protagonist of the old tongue- twister—‘She sells sea-shells.”

When she was a little girl, but twelve years old, she discovered, while searching for fossil shells, the first skeleton of the marine fossil reptile, Ichthyosaurus. That was in 1811. She became interested in the fossil reptiles of the marine Jurassic beds of southern England, and from that time on she was ever on the lookout for skeletons. After the death of her father, Mary Anning continued the business of collecting fossil shells for the tourist trade, but her real interest was in the bigger vertebrate game. To make a long story short, she embarked upon a career of fossil reptile collecting, and she made good in a field that has been since its beginnings a man’s game. In 1821 she found the first Plesiosaurus skeleton, and in 1828 she discovered the first skeleton of a pterosaur, or flying reptile, to be un- earthed in England. She collected numer- ous fine specimens of ichthyosaurs and

7

plesiosaurs and sold them to various indi- viduals and institutions throughout the world.

Some mention should be made at this piace of Charles Darwin (1809-1882) and his great disciple, Thomas Henry Huxley (1825-1895). Darwin, who must rank as one of the greatest men of all time, was not primarily a student of fossil reptiles; or of dinosaurs in particular, but it was his con- cept of organic evolution that revolution- ized scientific thought throughout the en- tire field of Natural History. Since the publication of Darwin’s Origin of Species in 1859, man has come to look at dinosaurs and all other remains of extinct life in a very different light than he had previously viewed them. Our modern understanding of the development of life on the earth is based upon Darwin’s work; our philosophy has grown from the stem of Darwin's great philosophical truths. Of all the great stu- dents of Life, Darwin was the greatest.

Huxley worked ably and hard in the years following the publication of the Origin of Species as a champion of Dar- winism. He was a brilliant scholar. He de- voted considerable attention to fossil reptiles.

At about the time that Cuvier and Mantell were working in Europe, some queer, three-toed tracks were being found in rocks of Triassic age, in the Connecticut Valley. They excited the particular interest of Professor Edward Hitchcock, of Amherst Coilege. He collected and studied examples of the fossils, many of which are still to be seen in the collection of the Amherst Col- lege Museum, and he came to the con- clusion that these tracks had been made by some large, extinct birds. Later it was realized that these were actually tracks of early dinosaurs and other reptiles, so that

18

i

Hitchcock may be considered as one of the first collectors on this continent of dino- saurian remains (or at least the evidences as to the existence of dinosaurs), even though he at first did not realize the sig- nificance of his finds. Of course Hitchcock’s mistake is readily understandable, when it is remembered that in his day dinosaurs were virtually unknown and when it is realized that the tracks he saw, those of two-legged dinosaurs, closely resemble large bird tracks.

However, the first dinosaur skeleton to be discovered in North America was found, of all places, in a suburb of Philadelphia, the little town of Haddonfield, New Jersey. The fossil first came to light during the course of some excavations in a marl bed, and it immediately was an object of curiosity to the diggers, to their sisters and their cousins and their aunts, and to the public in general. As more bones of the animal came to light they were carted off as souvenirs, so that many of them came to rest on New Jersey mantelpieces, or served as doorstops in Pennsylvania homes.

Some years later, in 1858, this discovery came to the attention of Mr. W. Parker Foulke, a Philadelphian interested in the subject of Natural History in general and in the Philadelphia Academy of Natural Sciences in particular. Mr. Foulke re- opened the excavation where the fossil had been partially disinterred, and he found a great deal more of the skeleton.

The skeleton, or such of it as still re- mained, was placed by Mr. Foulke in the Philadelphia Academy of Natural Sciences, where it was studied by the American paleontologist and anatomist, Dr. Joseph Leidy (1823-1891). Leidy, a man of great ability and learning, may be said to have been the founder of the science of verte-

MODERN

Joseph Leidy (1823-1891) inaugurated the Edward Drinker Cope (1840-1897), of period of continuous research in vertebrate Quaker ancestry, was a leading pioneer in the paleontology in North America search for fossil animals in our West

Othniel Charles Marsh (1831-1899) had a Henry Fairfield Osborn (1857-1935) organ- genius for organization and led many fossil ized vertebrate paleontology on its modern hunting expeditions into western North basis with a staff of highly trained experts at America. He and Cope were scientific rivals the American Museum of Natural History

19

brate paleontology in North America; it was from the beginnings he made in the subject that the science has continuously developed and grown to its present stature in this country. He was for many years Professor of Anatomy at the University of Pennsylvania and in addition served on the scientific staff of the Academy. While work- ing on this fossil, Leidy was able to trace down some of the “souvenirs” and add them to his skeleton, although, unfortunately, many of the vertebrae and other parts first discovered were irrevocably lost. Neverthe- less, the better part of the skeleton was obtained. It is the skeleton of a duck-billed dinosaur, Hadrosaurus.

In spite of the good work of the pioneer paleontologists during the first half of the nineteenth century, there was then no con- certed program of fossil collecting in North America. This phase really began after the War Between the States when the great expanses of the West were being opened. At that time the United States Government instituted a series of “Territorial Surveys” of the West, in an effort to assess after a fashion the natural resources of the strange new land. The emphasis of these surveys was on the geological side, and a result was the discovery of many fossil localities. Arrangements were made whereby the fossils would be studied by two men who had independently begun to conduct and direct some ambitious collecting trips in the western territories. These men were Edward Drinker Cope of Philadelphia, and Othniel Charles Marsh of Yale University, and with them there began a new, inter- esting, and highly exciting period in American paleontology.

Edward Drinker Cope (1840-1897) was a man of extraordinary brilliance and ability; in fact, he was one of the greatest

20

scholars that this country has ever pro- duced. He was of Quaker ancestry, the descendant of an old and prominent Phila- delphia family, yet in spite of his many gifts of position, wealth, and intellect he was a person of erratic temperament, a fact which conditioned many of his actions in later life.

Othniel Charles Marsh (1831-1899), a man of perhaps lesser intellect than Cope, was nevertheless a scholar of ability with a genius for organization. Like Cope, Marsh was a man of considerable wealth.

At first Cope and Marsh were friends, but when their work began to reveal the fossil wealth of the West, they soon became rivals, and eventually bitter enemies. They organized their own expeditions to collect fossils. Year after year, during the quarter- century between about 1870 and 1895, Cope and Marsh had exploring parties in the field, delving into the virgin fossil lo- calities of the great Plains and of the Rocky Mountain basins. It was a race to see who could get the most material and describe it—a race that now seems fruitless, since we have come to learn how abundant are the fossils to be found by the trained and dili- gent fossil hunter. There is enough ma- terial for everybody. But Cope and Marsh didn’t think so, and they engaged in a cutthroat competition which was perhaps one of the bitterest scientific feuds in his- tory. The result was that both men pub- lished a great deal, much of which was good, some of which was bad; and two great fossil collections were built up. And in these collections dinosaurs loomed large.

It was the first attempt at large-scale, long-term, planned collecting of fossil vertebrates—collecting that envisaged a series of expeditions over a number of years to predetermined localities. New horizons

were revealed to the world of science, and assemblages of fossils were recovered that literally astounded scholars throughout the world.

Perhaps the rivalry between these two men stimulated each of them to efforts much greater than they would have made if all had been sweet and serene. However that may be, the fact is that the work of Cope and Marsh, added to the earlier work of Leidy, formed the basis for modern vertebrate paleontology in America, and in the world for that matter, because these men established entirely new techniques of collecting, preparing, and studying fossils. Men such as these have transformed verte- brate paleontology from a comparatively passive science, based upon the chance dis- covery of isolated data, to a vigorous, active branch of study which owes its modern success to long-range co-ordinated plan- ning of world-wide scope. And in this field of scholarly endeavor America has played a leading role, thanks in part to the solid foundations built by Leidy, Marsh, and Cope.

What might be termed the modern period in the exploration and study of dino- saurs and other fossil vertebrates had _ its beginnings in the last decade of the nine- teenth century. At that time a generation of younger men who had been students of Marsh or Cope came to the fore in this country, while in Europe the subject was being expounded to enthusiastic students by such great authorities as Huxley in England and von Zittel in Germany. Co- incidentally there was a flowering of the larger Natural History museums in America and in the Old World, with the consequent opening of opportunities for fossil collecting on an adequately planned and_ well- executed scale.

The beginnings of the modern period in America may very well be dated by the entrance of the American Museum of Natu- ral History into the field of active fossil collecting and research. In 1891, Professor Henry Fairfield Osborn left Princeton University and came to New York to estab- lish a new department of vertebrate paleontology at the American Museum. Osborn, with his lifelong friend Professor William Berryman Scott, was a disciple of Cope and had studied in Europe under Huxley and other famous teachers. With his arrival in New York, the American Museum began a vigorous program of active work in the field of vertebrate fossils, a program in which the collecting, study, and exhibition of dinosaurs played a large and important part.

One of Osborn’s first acts was to gather about him a staff of highly competent men: Dr. Jacob Wortman, one of Cope’s as- sistants; Dr. William D. Matthew, a gifted paleontologist who will always stand as one of the leading figures in the annals of paleontology; Dr. Walter Granger, a collector who has never been surpassed; Dr. Barnum Brown, who has devoted his life to the collecting and study- ing of dinosaurs; Mr. Adam Hermann, who received his training in the preparation of fossils under Marsh; and under Hermann a corps of skillful preparators and collectors, notably Messrs. Albert Thomson, Charles Lang, and Otto Falkenbach. With a staff such as this the American Museum was bound to make great strides in the entire field of vertebrate paleontology.

Soon after Osborn’s association with the American Museum, the institution was able to purchase, through the munificence of Morris Ketchum Jesup, the great collec- tion of fossils amassed by Cope during the

American

21

years of his most active collecting trips—a collection upon which Cope had spent his entire personal fortune and the most pro- ductive years of his life.

Late in the 1890's a series of expeditions for dinosaurs was inaugurated at a locality known as “Bone Cabin Quarry” in Wyo- ming. Here the great skeleton of Bronto- saurus and many other fossils of Morrison age were recovered, and from that time on, the American Museum has collected many of these great Mesozoic reptiles, much of the work being done under the supervision of Barnum Brown. Expeditions have ranged far and wide over the western part of North America, in Wyoming and Colo- rado, in Arizona and Texas, in Montana and Alberta. Collections have been made in the deserts of Mongolia and South Africa. Exchanges have been made with museums throughout the world. The result is that the American Museum now has a collec- tion and an exhibition of dinosaurs and of many other fossil reptiles that is absolutely unsurpassed.

But during this period there have been other institutions making great strides in the excavation, study, and exhibition of dinosaurs and other fossil reptiles.

There is, of course, the Peabody Mu- seum of Yale University, where the fossils gathered together by Marsh are housed. Here is one of the earliest great assemblages of dinosaurs, a collection which is still of prime importance, and which has formed the background for the researches of Pro- fessor Richard Swann Lull, one of the lead- ing American authorities on dinosaurs. The United States National Museum, due to the long-continued and_ persistent efforts of Mr. Charles W. Gilmore, one of the great modern authorities, has also given attention

to the dinosaurs.

22

Early in the twentieth century Andrew Carnegie became interested in dinosaurs, with the result that the Carnegie Museum in Pittsburgh embarked upon a period of intensive dinosaur work. As a result a tre- mendous quarry of Morrison age was ex- cavated in eastern Utah, and a great amount of material was taken to Pittsburgh for preparation, study, and display. At the same time the Field Museum of Chicago (now the Chicago Natural History Mu- seum) was exploring for dinosaurs, with satisfactory results.

In more recent years the National Mu- seum of Canada, in Ottawa, and the Royal Ontario Museum, in Toronto, have carried on extensive programs of dinosaur collect- ing, particularly in the fossil fields of Alberta. Fine exhibits of dinosaurs may be seen in these museums.

‘Thus it may be seen that there has been in this country since the beginning of the present century a vigorous program of dinosaur collecting among some of the larger museums, and the result is that in no other country can such a variety and number of dinosaurs be found on display.

Some mention should be made of the work on fossil reptiles other than dinosaurs. Many years ago, Cope made extensive col- lections in the Permian beds of Texas, and as a result of his studies he showed how important the early reptiles of Permian age are in drawing up a complete and satisfac- tory picture of reptilian evolution. With the coming of the Cope collection to the American Museum, the foundations for an important Permian collection were estab- lished. In those early days of paleontology many Permian and _ Triassic reptiles were being discovered in South Africa, and were being described by Sir Richard Owen and other authorities at the British Museum.

Professor Osborn realized the importance of having the South African fossil reptiles represented in the American Museum, so he instituted a policy of acquiring such specimens. As a result the American Mu- seum possesses an important collection of Permo-Triassic reptiles from the Karroo desert, collected for the most part by Dr. Robert Broom, a South African authority on these ancient vertebrates.

More than a half-century ago one of Marsh’s students, Professor Samuel Wen- dell Williston, went from New Haven to the University of Kansas. There he built up an unexcelled collection of aquatic reptiles from the Niobrara Cretaceous beds of Kansas, a work which so enhanced his scientific reputation that he was called to the University of Chicago as Professor of Paleontology. There, with the able assist- ance of Mr, Paul Miller, he instituted a program of Permian work extending over many years, and assembled an outstanding collection of early amphibians and reptiles. This collection is now at the Chicago Nat- ural History Museum.

Other American institutions have im- portant fossil reptile collections, notably the Museum of Comparative Zoology at Har- vard University, where much work has been done on Permo-Triassic reptiles in recent years under the able direction of Professor Alfred S. Romer; the Museum of Paleontology of the University of Cali- fornia, with fine Triassic collections made under the guidance of Professors J. C. Mer- riam and Charles L. Camp; and the Mu- seum of the University of Michigan, in which are to be found Permian and Triassic reptiles and amphibians collected and studied by Professor Ermine C. Case.

What is to be the future of fossil collect- ing? Many years ago it was thought by

certain scientists that when intensive col- lections had been made, the fossil “lode” would, so to speak, “peter out.” But the more the fossil fields are worked the more they produce, and all the time new fossil fields are being found. Chinese paleontolo- gists, in the midst of war and tribulations unequalled in human history, discovered a dinosaur skeleton in Yunnan Province in the year 1938, excavated it, brought it to Chungking, and published a descriptive monograph in 1942. Which goes to show that fossils will out, whether there be flood, fire, famine, pestilence, or war.

One thing is sure, fossil collecting will go on as long as man remains a curious animal. And the search for dinosaurs, their contemporaries, and their forebears will be carried to the most distant reaches of the globe, to the Americas and Europe, to Asia and Africa and Australia. It is one field of collecting in which there is never any danger of extinction of the supply, where wise and co-ordinated policies will furnish ample collections for everybody.

A list of museums in North America where fossil amphibians and reptiles may be seen on display is presented below.

1. AMERICAN MusEuM oF NATURAL His- TORY, NEw YORK.

The exhibits are dominated by skeletons and skulls of dinosaurs, but there are also important displays of other fossil reptiles, notably pelycosaurs, mam- mal-like reptiles, thecodonts, turtles, crocodilians, ichthyosaurs, plesiosaurs, and flying reptiles.

2. UNITED StTaTEs NATIONAL MUSEUM,

WasHIncTOoN, D.C.

Here are found many notable displays of dinosaurs, some of which were collected and studied by Pro- fessor Marsh. There are also exhibits of Permian reptiles, turtles, and in addition some unusual specimens of fossil lizards.

23

38. PEABopy MusEUM OF YALE UNIVERSITY, New Haven, Conn.

The Peabody Museum collection is particularly important for the wealth of dinosaurs that it con- tains. A number of fine skeletons are on display.

4. MusrEuM OF COMPARATIVE ZOOLOGY OF Harvarp UNIVERSITY, CAMBRIDGE, MASss.

The exhibits at this museum are noteworthy be- cause of the Permian forms that are shown. There are also some important displays of aquatic reptiles.

5. ACADEMY OF NATURAL SCIENCES, PHILA- DELPHIA, Pa.

Some fine specimens of ichthyosaurs and _plesio- saurs, collected in England about 100 years ago.

6. AMHERST COLLEGE MusEUM, AMHERST, Mass.

A mounted skeleton of the duck-billed dinosaur, Trachodon.

7. NATIONAL MusEUM oF CANADA, OT- TAWA.

At this museum is housed a particularly fine exhibit of dinosaurs from the Cretaceous beds of western Canada.

8. RoyAL ONTARIO MuSsEUM, TORONTO, CANADA.

A notable display of dinosaurs from the upper Cretaceous beds of Alberta.

9. CARNEGIE MusEuM, PitrsspurcH, Pa.

The fossil reptile exhibits in this museum consist for the most part of an extraordinary series of Jurassic dinosaurs, collected in the Morrison beds.

10. MusEUM OF PALEONTOLOGY OF THE UNI- VERSITY OF MICHIGAN, ANN ARBOR, MICH.

A notable collection of Permian and Triassic am- phibians and reptiles from Texas and adjacent re- gions.

24

11. Cuicaco NaturaL History Museum, Cuicaco, ILL.

At this museum may be seen some specimens of dinosaurs. Here, without doubt, is to be seen the finest display of North American Permian verte- brates in existence. There also are some important reptiles from the Karroo beds of South Africa.

12. DycHE MusEUM OF THE UNIVERSITY OF Kansas, LAWRENCE, KANS.

The fossil reptile collection in this institution is noted for the skeletons of the aquatic mosasaurs, from the Niobrara Cretaceous beds of Kansas. 13. University OF NEBRASKA Museum, LIN- COLN.

Mounted skeletons of Stegosaurus and of a mosa- saur.

14. Texas MemMoriIAL MusEuM, AUSTIN.

Permian vetebrates.

15. SouTHERN METHODIST UNIVERSITY, DAL- LAS, TEX.

Permian vetebrates, plesiosaur.

16. Cotorapo Museum or Natura His- TORY, DENVER, COLo.

Several dinosaur skeletons are on display in this museum.

17. Universiry or UTAH, GEOLocIcAL Mu- SEUM, SALT LAKE City.

Mounted skeleton of Allosaurus, dinosaur bones, tracks.

18. MusEuM OF PALEONTOLOGY OF THE UNIVERSITY OF CALIFORNIA, BERKELEY, CAL.

The fossil reptiles are mainly those found in the Pacific coast and the southwestern regions of the United States.

19. CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CAL. Reptiles from the Pacific coast region.

3

Hunting Dinosaurs

NE OF THE QUESTIONS most fre-

quently asked of the paleontologist

is, “How do you find these fossils?” Indeed, it is puzzling to the uninitiated how the paleontologist will announce in the spring that he is going out to hunt fossils and then go to some distant region in the summer and make good his promise. How does one know where to look for the things? How does one go about it? Does one start by digging a hole in the ground, which mysteriously brings to light a new and strange variety of dinosaur?

There is nothing really mysterious about the process of hunting—and finding—dino- saurs, or other fossils for that matter. The technique is mainly a combination of good geological judgment, horse sense, persever- ance, and hard work.

The first requisite for the dinosaur hunter is to know where he should begin to look for the fossils. The dinosaurs lived during the Mesozoic age of Earth History; it necessarily follows that their remains will be found in rock strata of Mesozoic age, and nowhere else. (By the same token, if one is looking for primitive fish, attention is limited to early Paleozoic rocks, while if the search is concerned with the more ad- vanced mammals, the regions explored are those where Cenozoic rocks are exposed.) Of course in the early days of fossil hunting it was pretty much a hit-and-miss affair, because the science of geology was so young that the rock layers of various ages were not well known nor were they ade- quately mapped. .

The early expeditions of the Territorial Surveys and those of Cope and Marsh

worked to a certain degree in a blind way, because the territory they were exploring was essentially a new region. And the same is true, although to a continually lesser degree, at the present time whenever ex- peditions go into relatively unknown parts of the earth—as for example the Central Asiatic Expeditions of the American Mu- seum of Natural History to Mongolia. For many regions, however, the rocks of the earth have been studied and mapped in a fairly adequate that the paleontologist goes to localities where he will be reasonably certain of finding fossils of the type in which he is interested.

The entire procedure is really a rather

manner, so

interesting process of round robin reason- ing. Most of the sedimentary rocks of the earth’s surface are dated by the fossils they contain. Thus it is that in a new area, the first clues to the age of the beds exposed are obtained from fragmentary fossils, found haphazardly and by chance during the course of general exploratory work. Having thus established the age of the beds exposed in the new region, and having determined the extent of their exposures, subsequent work is carried out in a sys- tematic way with definite ends in mind. Perhaps a season of intensive search for fossils fails to justify the hopes first enter- tained by the enthusiastic bone hunter. If so, the summer’s work must be written off as “good experience,” and fossil-avid eyes But the paleontologist of good judgment will rarely embark upon a program of intensive work unless he is pretty sure that the results will justify the expenditure of the time and

are cast in other directions.

25

money that are allotted to him; consequent- ly the results. obtained by most fossil ex- peditions are fairly consistently satisfactory.

Having picked a region for exploratory work, the fossil hunter follows a definite and systematic procedure for ferreting out the dinosaurs, or fishes, or phytosaurs, or mammals, or whatever he may be after. First, by a method of trial and error, he learns just which levels or “horizons” in the rock layers are the fossil-bearing ones. Then he “walks out” the level, with one eye peeled for the precious fossils he is seeking,

/

the other busy searching for the next place to step. Which latter is more important than it may sound at first, for much of the business of “walking out” a formation in- volves a constant scramble along cliff faces, up and down the sides of canyons, in and out of arroyos or washes.

Of course it is important for the fossil hunter to know just what he is looking for— indeed, much of the secret of successful collecting is the recognition of a fossil as it is exposed in the strata, usually with merely a trace of the entire organism show-

Sometimes only an imprint of the skin is preserved. Here the skin itself Dero has been replaced by minerals. (From a Duck-billed Dinosaur) SKI

Here the form of the animal is retained as well as the skeleton: a fine example of the preservation of soft parts. (An ichthyosaur)

A.M.N.H. photogranbs

; Beneath the skin, a coat of mail protected this yT1' c animal and was fossilized. (A nodosaur)

27

One of the rarest fossils: a dino- saur egg over 60 million years old, compared with a hen’s egg (left) and an alligator egg (right)

28

A typical example of the parts usually found fossilized: portions of the skeleton of a small dinosaur from Mongolia

A.M.N.H. photographs

: : Fairly common are tracks made by dino- footprint saurs in mud and later changed to stone. This one held eighteen gallons of water

Photograph by courtesy of Roland T. Bird TE talc RE oe

+ Paha

ing. And that brings us to the question of “What is a fossil?”

A fossil is the remains or the indication of past life upon the earth. Originally the word fossil, derived from the Latin fossilis (dug up) applied to anything dug out of the earth, whether it were the remains of animal or vegetable life, or minerals. In modern usage, the term fossil is restricted to the remains or indications of organisms which once lived on the earth.

Fossils are preserved in a variety of ways. Usually fossils are replacements in stone of

materials which were originally organic. |

A living animal, a sea-shell, a fish, a dino- saur, a mammal, died and its body was covered by the ooze of the ocean bottom, by the mud of a shallow river, or by the shifting sands of a desert. Thus entombed, decay of the organic materials oftentimes was retarded, especially as regards the hard parts, such as shell or bones. Consequently the breaking down of these hard portions of the organism was a slow process. And if conditions were just right, it was accom- panied by another process, namely the re- placement of the original material by mineral matter, deposited by the waters that percolated through the sediments in which the animal was buried. This replace- ment was complete and molecular in nature, so that not only the external shape of the shell or the bone was preserved in rock, but also the internal microscopic structure. So it is that we are able to study a thoroughly mineralized fossil shell or bone just as com- pletely as if we had the original shell or bone to look at.

Such is the form of many fossils, but not by any means all. For instance, some fossils are actually the original shells and bones, with little or no mineral replacement. This is often the case with fossils of a relatively

_ 30

t

recent age, in which there has not been time for fossilization or “petrification.” Al- though the remains are not mineralized, they are nonetheless fossils, because they represent the remnants of something that was once alive on the earth.

Some fossils are found as molds or casts. In these instances, the original organism has decayed or dissolved, leaving a hollow impression in the sediment or the rock in which it was entombed. The hollow impres- sion is a mold. If that mold becomes filled with sand or mud, which « eventually solidi- fies to form stone, a cast_is- produced, a fossil which preserves the external form but not the internal microscopic structure of the original.

In some cases even the soft parts are fossilized, although this is unusual. When we find a fossil of this type we can be sure that conditions were such that the soft parts were protected in some fashion against im- mediate decay, while mineralization was comparatively rapid. On page 26 the fos- silized skin of a Duck-billed Dinosaur is pictured.

Sometimes fossils are formed by unusual minerals, such as iron pyrites, or opal.

Many fossils are not the remains of the animals or plants, but merely the indica- tions of such organic structures. Fossilized tracks are fairly common. Often fossilized burrows are found, or fossilized insect nests. Even the marks made by leaves brushing across the mud are sometimes preserved as fossils.

So it is that fossils may assume a variety of forms, and the fossil-hunter must be able to recognize fossils of these several types in the field, and interpret them properly. That is why he keeps one eye peeled as he scrambles along the face of a very hard and high cliff, under a very hot sun, barking

=> Bad lands are good lands for fossil hunters. But rough cliffs like this one in Utah have scraped the shins of many a prospector who thought he saw some- thing just a little higher

A.M.N.H. photograph

les Once discovered, the ancient bones are uncov- ered by careful work with pick, awl, and brush. During this delicate operation, the fossil hunter must often en- dure scorching sun, sand- storms, and sudden showers

Photograph by Barnum Brown

From inaccessible loca- tions fossilized bones weigh- ing several hundred pounds can be taken to the wagon road only with difficulty. Careful engineering is nec- essary to ensure their safe transportation

A.M.N.H. photographs

€& Finally the prehistoric treasure is hurried on its way to the railroad platform and the museum, where it will be

er ad ae

-

his shins, tearing his trousers, and sun- burning his back.

Sooner or later he will find the traces of a fossil—perhaps some broken bits of bone or teeth, if he is out for dinosaurs. Then he looks around to see if he can locate the place that is producing these broken bits— the place where the more complete animal is buried. Usually he has little success, the broken bits were merely broken bits, the fragments of an isolated bone or tooth. (Skeletons have a disconcerting trait of getting thoroughly dismembered and scat- tered before they are ever fossilized.) But every now and then the fragments lead to something bigger—above his head 20 feet up on the side of the cliff some bones are protruding from the face of the rock.

Then comes the process of clambering up to the fossil and establishing a place to work, oftentimes with many a prayer for “sky hooks” to help the struggling bone hunter defy the law of gravity. After that there is the tedious business of removing the “overburden,” the tons and tons of rock that are usually piled on top of the fossil and must be gotten out of the way. That is one of the great gambles in fossil hunt- ing. Sometimes considerable effort will be expended in removing the overburden, only to find that the fossil “peters out” six feet in from the face of the cliff. But at other times the dreary work of picking, shoveling, hauling, and often blasting, will be re- warded by the exposure of a fine skeleton, or even a whole series of skeletons. Some- times fossils are found out on open flats, with little or no overburden. The fossil- hunter then offers fervent thanks to a benign providence for giving him (at least for one time) all gravy.

Then comes the work of exposing the fossil so that it can be removed. This in-

| 32

volves a careful uncovering of the bone with pick, hammer, awl, and brush, so that the extent of the skeleton may be judged. Usually when this work is being done the sun is uncommonly hot and the air still and stifling. Or it is windy enough to blow the harassed fossil hunter “into the next county,” and at every move he gets his eyes and mouth full of sand. Or there are a series of sudden desert rain storms that necessi- tate a series of frantic efforts to get the precious specimen covered by a canvas tarpaulin before it gets wet. Or there are flies and hornets.

At any rate, the work must be done, and done carefully. Every bone or tooth that is exposed must be shellacked and covered with tissue paper, otherwise it is apt to crumble to powder. Then the skeleton is removed, bone by bone, or else in blocks each containing several bones. To do this it is necessary to cover the part being re- moved with strips of burlap dipped in liquid plaster or in flour paste. When the burlap and plaster or paste covering has dried and hardened, it forms a strong cast over the bone or the series of bones, and thus prevents the fossil from breaking when it is moved. In other words, the fossil is “immobilized,” in the same manner that a broken arm or leg is immobilized by a doc- tor. Then, when the top and sides of the specimen have been so secured, it is care- fully freed from the rock on which it is rest- ing, turned over, and the bottom is encased in the plaster and burlap bandage or cinch. If the specimen is very large, sticks of wood, or splints, are attached to the bandaged fossil to keep it from breaking of its own weight.

Next the fossil has to be moved to a suitable place and packed in a wooden box, in straw. Then the box is hauled to the

==> In the museum lab- oratory, the shellacked wrappings and the excess rock are removed from the fossil. This requires skill, patience, and great delicacy of touch

A.M.N.H. photographs

W ittusteations of the fossil for publication in- clude not only photo- graphs but caretul draw- ings made by scientific

artists

nearest railroad shipping point, and the specimen begins its trip to the museum. When one is hunting dinosaurs, which are usually found in the most out-of-the- way places possible, and which often have single bones weighing two or three hun- dred pounds, the difficult nature of the work of fossil-hunting becomes painfully apparent. But in spite of the hard and hot work, the sand and the flies, the bad water, and the many natural discomforts that flesh is heir to, the fossil-hunters love it. Take a paleontologist’s field trips away from him and he is apt to get savage, or at least to acquire a rather sour outlook upon life. Collecting the fossil and sending it to the museum is only part of the story. In the

Leet,

a

oF Wags i \ ¥ Wis

‘< :

museum the entire process that was gone through in getting the specimen out of the rock has to be reversed. First the fossil must be unpacked. Then the burlap and plaster cinches must be removed. After that there comes the long process of “preparing” it for study or exhibition. The bone must be freed completely from its rock matrix, a pro- cedure that requires skill, patience, and a great delicacy of touch. Indeed, the process of preparation is usually the longest and most tedious part of paleontological tech- nology. As the rock is chipped away from the bone, the fossil is hardened with shellac. Large bones are drilled, and steel rods are inserted into them to support their dead weight. Missing parts are filled in with plaster. Thus it may be seen that the preparation of a fossil skeleton is a long job, and when the work involves some- thing as large as a big dinosaur, the task is truly colossal, requiring the full-time efforts of several skilled men for many months, or even years. That is why only the large institutions are able to go after the big game of dinosaurs.

After the fossil is fully prepared, the paleontologist at last begins his examina- tion of it. The fossil must be compared with other fossils, and identified. Perhaps it is new. Then it must be carefully studied and a description written for publication in a technical journal. For it is only through publication that a fossil collection has any real value. Unless the information gained from the collecting and preparing of fossils is made available through the printed page, the assemblage of specimens is essentially

a pile of meaningless junk. The reputation of a scientist and of the institution for which he works depends largely upon his publications. Without a solid foundation of scientific publications emanating from its

<& If the extinct animal is to be placed on exhibition, the skeleton is mounted in posi- tion. The bones may have been greatly dis- arranged when found; here they are accurately assembled and held in a natural posture by concealed supports that will be scarcely visible when the scaffolding is removed

A.M.N.H. photograph

activities, a paleontological museum is not a museum but merely a warehouse or a showplace. Thus the publication of the studies made on the fossils is one of the most important functions of the museum. The scientist studies the material and pre- pares a manuscript. A trained scientific artist working with him makes drawings of the fossils to illustrate the publication. To- gether they produce the scientific paper which makes the information on the fossil available to students all over the world, and gives to it its true value.

If the specimen is sufficiently well pre- served, and of sufficient importance, it will be placed in the exhibition hall. Only the more choice fossils, however, are placed on public exhibit; the bulk of the collection is retained in storage for study and future reference. This is modern museum practice, for we now believe that exhibits should tell a story by well chosen examples, rather than serve as dismal arrays of specimens on shelves, which was the philosophy of mu- seum display a half-century or so ago.

If the specimen to be exhibited is a skele- ton, it must be properly assembled, and this again is a job requiring a great deal of skill and considerable time. Irons must be bent to support the bones, and fastened together to make a sort of frame upon which the skeleton is hung. The preparator and the scientist work together on this, and oftentimes the job requires a great deal of supplementary study in order that the pose will be anatomically correct and at the same time interesting. But they keep at it in the museum laboratory, and after weeks or months of work the specimen finally stands articulated, a thing of real structural beauty, ready for the exhibition hall.

But the end may not yet be in sight. For the paleontologist may decide that a painted restoration is needed, to show the

museum visitor how the dinosaur or the phytosaur or the pterosaur looked in life. So, that long-suffering and patient being, the artist, is called in again, this time to project himself in his mind’s eye back to a distant age, to make a portrait of a beast long since gone from the face of the earth. He works with the paleontologist on this. Together they compare the fossil with the nearest related animal extinct or living. Together they figuratively hang muscles on the bones and then stretch a skin over the muscles and then brush a color over the skin. At last the animal stands as he may have appeared in life, and in all fairness it must be said that there is every reason to believe that a careful restoration made by a competent artist, working with a com- petent paleontologist who knows his anatomy, is pretty close to the truth. There remains only the task for the artist of putting in some contemporaneous scenery and vegetation (and that is no mean job), and the restoration is ready to go on exhibi- tion along with the fossil, or in a book such as this.

But is that all? Not quite, for the labels must be written. One explanation of a good museum exhibit is that it consists of a series of excellent labels illustrated by good speci- mens. Well, the labels are prepared, and then the exhibit is ready, at long last.

It has been a long story, from the fossil in the field to the exhibit in the hall, a story involving the expenditure of many man- hours of time by various trained persons. But in the end the results are worth the price, for we have learned more about the past history of the earth and the proper interpretation of our modern world depends greatly upon our knowledge of its past.

Some of the more important localities at which fossil amphibians and reptiles have been found are discussed in Chapter 17.

35

4

The Age of Reptiles

E ARE LIVING in the Age of Man,

the period in which man rules the

earth. For better or for worse we are supreme over all other forms of life. No longer is our existence threatened by large animals, as was the case with some of our not very distant forebears. No longer are we so seriously threatened by the less spectacular but much more deadly micro- scopic parasites, as were our ancestors of a few hundreds of years ago. There is nothing to challenge the supremacy of man upon the earth, except man himself.

It is readily understandable that having achieved this supremacy, we are apt to think of ourselves as the culmination of evolutionary history. And from our present- day standpoint this is true. No animal in the history of the earth has risen to the supreme dominance over the lands and the waters that is ours. Therefore, we can say that no animal, to our way of thinking, has been so successful as we are.

Yet there is another way of looking at this matter. Let us forget our natural bias as human beings and regard the question from an objective viewpoint.

Many ages ago, in the dim past of Earth History, lived the dinosaurs. These animals arose, evolved, and became extinct at ages so far distant from us that we can hardly stretch the imagination sufficiently to com- prehend the immense passage of time that separates them from us. Since they are gone from the face of the earth, we are inclined to regard them as “failures” in the long history of life. Were they really failures?

Man has lived on this earth for perhaps

36

a half-million to a million years, which seems like a long time. Of that great period, man has written the last seven thousand years of it into his record; before the period of recorded history man was a primitive savage, wresting his living from the soil and from the chase, ever surrounded by large beasts that challenged his right to the fields and forests.

The dinosaurs lived for a period of about 100 million years, during which time they

‘were the dominant animals of the earth.

For a period at least 100 times as long as the entire history of man, these ancient animals lived and fought and died—the lords of creation. Who are we to say that they were not successful?

Perhaps you are wondering about the rather casual bandying about of time figures so astronomical as these. What right have we to say that the dinosaurs lived so many millions of years ago, or that they persisted for so many millions of years?

This brings us to the subject of geologic time.

The immensity of geologic time is so great that it is difficult for the human mind to grasp readily the reality of its extent. It is almost as if one were to try to under- stand infinity.

The earth is about two billion: years old This is not a mere guess but is the result of careful, cumulative studies by many investi- gators working over a long period of years and along various lines of evidence. Of particular use are the investigations of radioactive materials in rocks of ancient age—indeed, it is by the study of the slow

disintegration of radium and uranium into lead that we have extended our conception of geologic time to its present tremendous limits.

Of the two billion years of Earth History, only about one-fourth, or 500 million years of it contain adequate fossil records. In other words, 500 million years ago life on the earth had reached a stage so that the remains of plants and animals were of suf- ficient density and complexity as to be pre- served in the form of fossils. In this 500- million-year fossil record we find the dinosaurs appearing some 170 million years ago and persisting through a period of about 100 million years’ duration, to be- come extinct about 70 million years ago.

Perhaps these are mere figures. Let us look at the record in another way.

The recorded history of man goes back about seven thousand years, to about the time of 5000 B.C. Within this stretch of time are encompassed the events of history, as we know them, from the rise of the early civilizations of the Middle East to the present stage of our modern machine age.

The days of ancient Egypt seem vaguely distant to us, yet as compared to the entire history of man on the earth they are as but yesterday, for man first appeared about one million years ago. The 7000 years of history seem indeed of rather insignificant propor- tions when compared with the one million years of prehistory as revealed by the science of archaeology.

Man, even in his most primitive mani- festations, is a relatively late product of evolutionary history, as compared with most of the life on this earth. Comic strips and jokes to the contrary, the dinosaurs had been gone and forgotten for a great many million years before man ever made his first appearance in a troubled world. In fact,

there was a time lapse of some 69 million years between the disappearance of the last dinosaurs and the appearance of man, as revealed by the science of paleontology.

The 70 million years during which the warm-blooded mammals attained their supremacy may seem like an immensely long stretch of time, yet it was only a little more than half as long as the reign of the dinosaurs on earth.

Carrying the story still further into the distant mists of geological antiquity, it may be seen that the age of dinosaurs, tremen- dously vast to our way of thinking, occu- pied but a fraction of the time since the first well-preserved fossils appeared in the geologic history of the world.

Finally, the period of fossil history is but one-fourth of the period of Earth History, as was mentioned above.

Just as our own written history may be subdivided into stated periods, marked by certain events or by certain series of events, so is geologic history divided by the se- quence of events of Earth History.

The Mesozoic era was primarily the age of dinosaurs. Of course, there were other types of animals living at that time: fishes and aquatic reptiles in the water, flying reptiles and primitive birds in the air, and small, archaic warm-blooded mammals on the land. But these animals, important as some of them might be in view of the subsequent history of animal life, played for the most part relatively insignificant roles in the great drama of Earth History during Mesozoic times. The real actors on this stage were the dinosaurs.

The Mesozoic is often known as the “Age of Reptiles,” since dinosaurs are reptiles and were dominant at that time. This, however, may not carry quite a true picture of things as they were, for as may be seen by the

37 |

DINOSAURS are extremely old when com-

pared with the earliest human remains. But they

are relatively late in the 2-billion-year history of the earth A.M.N.H. photograph

7 Age of Man 1 million years S MAMMB F ) , 5 Dinosaurs os extinct. Mammals appeared about 6 became dominant about 70 175 million years ago Seats years ago. SN g —— A or ~ \ : NX \\ +4 First reptiles appeared about \. \ 245 million years ago.

2 First land Oldest fossils vertebrates _ are about (amphibians) 500 million appeared years old about 280

million

years ago te ~<a Oldest dated rocks a about 2 billion

“NS rs ago.

1/50 inch = entire period

if 3 inches= Age of Man

(1 million years)

of recorded history

(5000 B.C. to present)

accompanying figure, the reptiles appeared on the earth approximately 245 million years ago (Late Paleozoic era), and were even then dominant on the land. So the “Age of Reptiles” might be thought of as extending at least from the beginning of the Permian period (about 225 million years ago), at which time the primitive reptiles had become well-established upon the earth, to the end of the Mesozoic era, when reptilian dominance ceased with the disap- pearance of the last dinosaurs.

Preceding this Age of Reptiles was an Age of Amphibians, including in a general way what the geologist refers to as Mis- sissippian and Pennsylvanian times. This

was the period during which the first land vertebrates were evolving from their fish ancestors. It was the period during which the basic patterns for reptilian evolution began to be established.

These, the Age of Amphibians and the Age of Reptiles are the periods of Earth History with which we shall be especially concerned in the following pages of this book. We are interested particularly in the dinosaurs, but in order to understand them properly it will be necessary to give some attention to their predecessors and_ their contemporaries. So it is that our story be- gins with the emergence of the vertebrates from their watery ancestral home.

39 |

ERAS ete PERIODS DOMINANT ANIMAL LIFE

Lot _# Y

Pleistocene

CENOZOIC Pliocene 70 million years Miocene

duration Oligocene Eocene

Paleocene

Cretaceous

MESOZOIC 120 million years duration

Esa

Permian

he 3)

Pennsylvanian

\\

Mississippian

‘Aiaphibiant

Devonian

N

SQ SS

PALEOZOIC

350 million years

duration

Ordovician

invertebrates

Cambrian

Pee Re see

PROTEROZ is me 1500 MILLION YEARS

DURATION

BEGINNINGS OF LIFE

ARCHAEOZOIC

3

The First Land Animals

E DO NOT KNOW when life began on the earth, and it seems likely that the answer to this question will remain forever hidden from us. What we do know is that it was some 500 million years ago when the plants and animals of early geologic history had reached a stage of development where they produced hard parts capable of being preserved as fossils. At that distant date there seemingly was no land life; all life was in the sea. More- over, there were no vertebrates, or back- boned animals, living—at least none of suf- ficient complexity that they left hard struc- tures to be preserved in the form of fossils. According to the fossil record, the animals of that time were mostly various types of sea-shells and crablike forms. It is probable, however, that even by the beginnings of Cambrian times, about 540 million years ago, the basic patterns for the backboned animals had been established, for it was at an early stage in the Paleozoic era that the first vertebrates appeared. These were primitive, fishlike forms. The fishes rose and evolved at a rapid rate, so that by middle Paleozoic times, in

Into a world of primitive backboned ani- mals came many kinds of fishes in the period between 275 and 340 million years ago. Among these, the crossopterygian or lobe-

the Devonian period (340-275 million years Fr iia Fi adannaedataaain the waters of the earth. There were many kinds of Devonian fishes, some large, some small, some fast-swimming and predaceous hunters, others flattened burrowers and grovelers in the muds of shallow bottoms. Among the Devonian fishes there were cer- tain ones, belonging to a group known as the crossopterygian (cross-op-ter-Ij-e-yan) or lobe-finned fishes, which were destined to play a very important role in the history of evolution, for these were the immediate, direct ancestors of the first land-living vertebrates.

The lobe-finned or crossopterygian fishes were of medium size and were covered by a heavy armor of scales. Some of the signifi- cant structures characterizing these early fish were:

a.

The arrangement of the bones in the skull according to a pattern that is comparable, bone by bone, with the skull pattern of the

early land-living vertebrates.

b.

The microscopic structure of the teeth,

finned group represented above by Os- teolepis were to become the direct ancestors of the first backboned animals to live on

land

€= Only during the last 500 million years have plants and animals produced hard parts capable of being fossil- zed. Here is a simplified chart of that quarter of the sarth’s history

Drawings by John C. Germann

which is virtually identical with the struc- ture of the teeth in the early land-living vertebrates.

Cc.

The presence of internal nares—the inner openings of the nose—a character found in land-living, air-breathing animals.

d.

The arrangement of the bones in the fins in a manner that is comparable with the arrangement of the bones in the limbs of the early land-living vertebrates.

The transition in the vertebrates from an

aquatic to a terrestrial or land-living mode of life was one of the great forward steps in_ evolutionary history. Indeed, it was _a step of such magnitude that it might be considered as an important revolution in the history of life on the earth.

Consider the facts. a The fish lives in a dense medium, which buoys it up. Therefore to the fish gravity is a problem of little consequence. But to the fand-living animal gravity becomes a prob- lem of the greatest consequence, because the body must support itself against a con- stant downward pull. b. The fish is prevented from drying up by the life-long bath to which it is subjected. In the air, on the other hand, there is constant evaporation, so that in the land-living ani- mal provision must be made against the drying up of the fluids within the body.

Cc:

The fish extracts oxygen from the water by means of gills. The land vertebrate develops in the lung a new means of obtaining oxygen from the air.

d.

The fish moves largely by means of rhyth-

42

mic undulations of the body, passing to the tail and acting against the dense water in which it lives. The fins are used mainly as balancing organs. In the land animals the paired limbs, derived from the fish fins, be- come the propelling mechanisms, while the tail, in part the propelling structure of the fish, becomes a balancing member.

e.

Finally, the fish lays its eggs in the water, by which medium they are kept moist and able to function for the purpose of hatching a new generation of fishes. In the land- living vertebrates there must either be a return to the water to deposit the eggs, or new methods must be developed for pre- venting desiccation and destruction of the new generation during its embryonic life.

The transition among vertebrates from life in the water to life on land took place in Upper Devonian times, about 300 million years ago. Certain crossopterygian fishes struggled out onto the land and the first land- living amphibians came into being.

The amphibians are those cold-blooded land animals which typically return to the water to lay their eggs. The young are hatched _as fishlike tadpoles and go through a_water-living, gill-breathing stage, after which they come out onto the land to live as air-breathing adults. We know them to- day as the salamanders, the toads and frogs, and certain legless tropical forms, the Gymnophiona, Coecilia, or Apoda (jim-no- fee-o-na) (see-SIL-ee-ya) (a-POAD-a).

The amphibians as we know them are the meek descendants of a long line, living their harmless lives in the shelter of the grassy banks that line our streams and ponds, or unobtrusively hunting insects in the leafy shadows of the garden or wood- land. However, for a geologically brief

Aississippian- Pennsylvanian. From 275 to 225 million

ae

J

°

_as labi

period of time—that time when the verte- brates were first invading the land—the amphibians enjoyed a period of terrestrial dominance, a period when they were the masters of the solid earth.

This dominance had its beginnings in the first venturings of vertebrates from an aquatic to a terrestrial mode of life, when there was nothing to dispute the claims of the primitive amphibians to the firm ground as a new environment. It had its beginnings with certain Upper Devonian forms such as Ichthyostega (ik-thee-o-sTEEG-a), an early

amphibian from Greenland that shows in its structure the heritage of its crossop- terygian ancestors.

The development of the Amphibia reached its culmination in a line of late Paleozoic and early Mesozoic er rinthodonts (lab-i-RiNTH-o-dont “named from the labyrinth-like aaa “structure of their teeth—a direct inheritance

4 e from their crossopterygian fish ancestors. 0\ The labyrinthodont amphibians appeared

c

in Mississippian times, seemingly as direct descendants from the ichthyostegids (see Ichthyostega, above), and they persisted through the Permian period, finally to be- come extinct in the Triassic some 170 million years ago. During this time they de- veloped so that some of them became rather large, the giants of their kind.

The evolution of the labyrinthodonts,

which is rather interesting, may be outlined

briefly as follows.

ary life in Mississippian and Pennsylvanian ans ies ee having relatively weak limbs. These early labyrinthodonts are known as the Embol- omeri (em-bol-o-mer-ee). From the Em- bolomeri there evolved large, robust, land-living types with strong legs, the Rhachitomi (rak-1r-o-n -‘me). The Rhachitomi, living in the Permian “period, were among the gore and most | powerful es we

would look as if Bere were ean cate to establish a successful line of aggressive land-living animals. Such, however, was not the case, for in Triassic times the evolution of the labyrinthodonts turned backward, so to speak, and these animals returned to a water-living mode of existence. These

‘ Triassic forms are known as the Stereo-

spondyli (ster-ee-o-spon-dil-ee), and they were the last of the labyrinthodonts. At the end of the Triassic they became extinct, and thus ended the bid of the amphibians for a position of dominance or partial dominance among the land-living animals.

Perhaps the evolution of these amphibi- ans may be made clearer by outlining it as shown below.

One of the best known and very charac- teristic labyrinthodonts was Eryops (ER-ee-

Evolution of the Labyrinthodontia |

years ago

Permian From 225 to 190 pultion years ago ee

CREATURES THAT LEFT THE WATER: The rise and decline of the labyrinthodont amphibians. The primitive labyrinthodonts, such as the Pennsylvanian form, Diploverte- bron, were long-bodied and rather weak- limbed animals, not so very far removed from their fish ancestors. The peak of labyrintho- dont evolution was reached in large, robust, rather aggressive Permian types, such as Eryops. Finally in Triassic times these verte- brates returned to the water from which their ancestors had emerged, so that the head and body became flat and the limbs were reduced in size and strength, as in Buettneria

Restorations by John C. Germann

Diplovertebron

ops). This large amphibian is found in the Permian beds of Texas, and as may be seen, it was a strong, heavy, land-living animal. Here was the high point in amphibian evolution. Look at Eryops and you see the culmination of development in the Am- phibia, an animal that was a truly dominant element in his environment. All that went before was building up to this climax in amphibian history, all that has come since is in a sense an anticlimax.

There were various amphibians con- temporaneous with Eryops. Some of them were small, active labyrinthodonts. Others were not labyrinthodonts at all, for at that time there were several lines of amphibian development evolving side by side. Per-

Buettneria

SA

haps one of the most interesting of the non-labyrinthodont forms was Diplocaulus

(dip-lo-kawL-us), belonging to a group

known as the Nectridia. This was a peculi-

arly flat, wide, water-living amphibian with an extraordinarily bizarre skull, shaped somewhat like a tremendously broad arrew- head.

The ancestry of our modern amphibians, though obscured in the mists of geologic time, is probably dual in pattern. There is indication that the frogs and toads are de- scended from a labyrinthodont stem, while the salamanders and perhaps the coecilians are derived from certain small, salamander- like amphibians of Pennsylvanian age known as lepospondyls (lep-o-spon-dils).

ss

The frogs and toads have become highly modified. The head is large, the neck and body short. The elongated hind legs serve as efficient springs to propel the animal in long leaps, while the short forelegs are firmly attached to the body and strength- ened, to take up the shock of landing. The tail, so typical of most vertebrates, has been lost. All in all these melodious friends of the swamp and stream are highly successful animals. They had their beginnings in Triassic times, and from the Jurassic to the Recent period they have persisted in es- sentially their present highly modified condition.

An extraordinary skull shaped somewhat like a broad arrowhead distinguished the early amphibian known as Diplocaulus

The salamanders are seemingly rather primitive amphibians that have returned to a life spent largely in the water or in moist places. Consequently they show a certain amount of “regressive evolution,” such as the secondary development of cartilage in parts of the skeleton that once were com- pletely bony. Some of the Pennsylvanian lepospondyls seem to indicate an ancestry for the salamanders.

It is possible that the Gymnophiona or coecilians also were derived from a lepospondyl ancestry, but since no fossils are known, the history of these small, leg- less, tropical amphibians must remain largely a matter of conjecture.

EVOLUTION OF THE AMPHIBIA. The pres- ent-day frogs and toads apparently descended from one stem; the salamanders (and perhaps the coe- cilians) from another

Restorations by John C, Germann

6

Primitive Reptiles

E HAVE SEEN HOW the amphibians arose, reached the culmination of their evolutionary development and for a geologically brief period enjoyed a certain degree of dominance among the animals living on the land. We have seen how this culmination and dominance of the amphibians was attained by the late Paleo- zoic labyrinthodonts, the giants, and in many ways the most highly evolved of these primitive land vertebrates.

The labyrinthodonts, in spite of their evolutionary progress, were unable to evolve to any great eminence because at an early stage in their history they suffered from the competition of other land verte- brates that were better adapted to a terrestrial environment than they were. These were the reptiles, the cold-blooded land animals in which the young develops directly without any tadpole stage.

The reptiles arose soon after the appear- ance of the labyrinthodonts and developed side by side with them. By Permian times there was actually a certain amount of “pushing and shoving” between the reptiles and the amphibians for elbow room upon the surface of the land. But the amphibians lost the battle; the last of the labyrintho- donts retreated once again to the primitive home for all life, the water, there to enjoy a brief respite of existence before they finally became extinct, while the reptiles, ever evolving and increasing, reached hith- erto unscaled heights in the climb up the evolutionary ladder.

Why did the amphibians lose the many

tionary race to the reptiles? The answer probably is to be found in one word, repro-

duction. The reptiles prevailed because in them a new method of perpetuating the species had evolved. It is probable that the labyrinthodont amphibians had to return to the water for the laying of the eggs, just as is the case with most of the amphibians of the present day. In the early reptiles, how- ever, it is probable that the specialized amniote egg had been perfected. Indeed, the appearance of the amniote egg was one of the great forward steps in vertebrate evolution, for with the development of this new type of reproduction the vertebrate was henceforth freed from its bondage to the water.

The amniote egg is, briefly, the encased egg of reptiles and birds: the egg in which the developing embryo is protected by an enveloping sac, the amnion, while the entire egg is generally enclosed in a hard, protec- tive shell.

The protected egg which presumably gave the early reptiles their initial advantage over the amphibians. Here for the first time the de- veloping embryo is freed from its prior bond- age to the water, by means of a hard, protec- tive shell and an enveloping sac (the amnion) —hence the name, amniote egg

From Romer’s Man and the Vertebrates, The University of Chicago Press

47

It was probably the development of this egg that marked the first divergence of the early reptiles from the amphibians, for just as certain fish were the progenitors of the amphibians, so were certain amphibians the progenitors of the reptiles. And the basic ‘reptilian grandparents were labyrintho- donts. Therefore, while the thesis of laby- rinthodont extinction before the onslaught of their reptilian competitors is valid, it is in a way equally valid to say that one branch of the labyrinthodont line was con- tinued by the reptiles because certain early labyrinthodonts were transformed into reptiles.

The first reptiles had great evolutionary

The “grandfather” of the reptiles: Sey- mouria. This animal formed an almost per- fect intermediate link between the early am- phibians and the ensuing reptiles, and repre- ~\sents the structural ancestral type from which all the reptiles evolved

Restoration by F, L. Jaques

potentialities. They were free of the water. They could venture over the face of the earth and continue their kind in regions where the less efficient amphibians could not survive. Thus was born a mighty race.

The earliest reptiles were very much like their amphibian ancestors. In fact, some of the most primitive reptiles were so very am- phibian-like that there has been a great deal of argument as to whether these basic rep- tiles might not more properly be regarded as advanced amphibians. So it goes. The more we know about the classification of animals, the less distinct become the lines of demarcation separating one form from another or one group from another. In other words, we find the intermediate stages which prove the validity of evolution.

Certainly there could hardly be an ani- mal more exactly intermediate in_ its anatomical features between the amphibi- ans and the reptiles than the Permian genus, Seymouria (see-Moor-e-ya), from the rocks known as the red beds of Texas. This animal approximates structurally the stem for all reptilian life; it is the “grand- father reptile.”

The reptiles may be classified in a broad, general way on the basis of skull design, as follows: ae Anapsida (an-Aps-i-da)

Skull roof solid, without any openings be- hind the eye.

b.

Synapsida (sine-aps-i-da)

Skull roof perforated by a lower opening behind the eye bounded above by the postorbital and squamosal bones.

Cc.

Parapsida (par-aps-i-da)

Skull roof perforated by an upper opening behind the eye, bounded below by the post-

frontal and supratemporal bones. eG

d. Diapsida (dye-aps-i-da)

Euryapsida* (your-e-aps-i-da) Skull roof perforated by a lower and an Skull roof perforated by an upper opening upper opening behind the eye, these open- behind the eye, bounded below by the ings separated by the postorbital and postorbital and squamosal bones. squamosal bones.

*T am indebted to Professor A. S. Romer of s : y ‘ Harvard University for the suggestion as to the une ES a elles were amapeids:. They MeEeeaoniand. ihe asevof thie name. were the reptiles with solidly roofed skulls,

THE FIVE BASIC TYPES of reptilian skulls. The anapsid skull had no openings behind the eye. The synapsid skull had a temporal opening behind the eye, below the squamosal and postorbital bones. The parapsid skull had a temporal opening behind the eye but above the supratemporal and postfrontal bones. The euryapsid skull had one above the squamosal and postorbital bones. The diapsid skull had two temporal openings behind the eye, separated by the squamosal and postorbital bones

Drawings by John C. Germann

|

Labidosaurus

Diadectes

Seymouria

From “grandfather” Seymouria, two general lines of reptiles descended. In one, the ani- mals remained small, like Labidosaurus. In the other, there was a tendency to giantism, as may be seen in Diadectes from North America and in the large pariasaurs from the Old World, one of which is shown opposite

Restorations by John C. Germann

an inheritance from the solid, bony skulls of their labyrinthodont ancestors. Of these anapsids, the first to appear were reptiles belonging to the order known as the Co- tylosauria (ko-rmLE-o-sawr-e-ya). The sey- mouriamorphs, typified by Seymouria, are perhaps the primitive ancestors of the coty- losaurs. Some authorities have included the seymouriamorphs among the labyrinthodont amphibians rather than among the primitive reptiles.

The cotylosaurs evolved through Permian and Triassic times and then became extinct.

50

Their evolution was divided along two lines of development. There was a line of small Permian cotylosaurs, showing certain specializations, known as the labidosaurs (LAB-i-do-sawrs) or captorhinomorphs (kap- to-RINE-0-morfs). In contrast the other group of cotylosaurs, known as the diadecto- morphs (dye-a-pEKT-o-morfs), consisted of quite large reptiles fiving in the Permian period, and small, highly specialized sur- vivors persisting through the Triassic period.

Labidosaurus was small, like Seymouria. It had the long body and the sprawling, weak limbs of the primitive reptile. The skull, as in all anapsids, was roofed over by solid bone, and was abruptly truncated be- hind. A characteristic feature of this animal was the overhung, or hooked upper jaw.

Diadectes (dye-a-DEKT-eez) was a rather large Permian reptile, some five or six feet in length. The legs were sprawling, as in the other primitive anapsids, so that this animal must have been rather clumsy when walking. Diadectes seemingly was a plant- eating reptile, for the teeth were blunt and peglike, and not at all suited to catching animals as were the pointed, spikelike teeth of Seymouria and Labidosaurus. A remark- able feature of Diadectes was the large pineal opening on the top of the skull, showing that this reptile had a very large “pineal eye’—an organ sensitive to light, which still persists in a much reduced form in the recent lizards and the tuatara (Sphenodon) of New Zealand.

Closely related to the American diadectids were the Permian pariasaurs (par-EYE-a-sawrs) of South Africa and Russia. These were really massive reptiles, as big as small cattle. Like the other large cotylosaurs they were seemingly plant eaters, large, heavy, and sluggish. They had

very broad, robust bodies and strong, heavy legs, and as in other primitive anapsids there was no clearly defined neck.

The last of the cotylosaurs, living through Triassic times, were diadectomorphs which were smaller than the large Diadectes of North America and the massive pariasaurs of Europe and Africa. Their development ran counter to the earlier trend towards giantism in this branch of the cotylosaurian reptiles. Known as procolophonids after the charac- teristic genus Procolophon (pro-Kot-o-fon), these animals evidently ranged widely throughout the world in Triassic times, since they are found in South Africa, central Europe, Scotland, and North America.

An early type of procolophonid is to be found in the Lower Triassic genus, Procolophon, of South Africa. Although small, Procolophon was robustly con- structed. It had a deep skull, narrow in the front and broad at the back. The pineal opening on the top of the skull was very large. The teeth were limited in number, and those in the back portion of both upper and lower jaws were somewhat broadened for chopping or cutting green plant food.

In Lower Triassic times the procolo- phonids appeared also in central Europe

where they had become specialized to the ex- tent that in some of them there were spikes on the sides or the back of the skull.

Finally, the Middle Triassic of Scotland and the Upper Triassic of New Jersey yielded the most highly specialized procolophonids, the last of the cotylosaurs. They were charac- terized by a flattening of the skull and an ex- cessive development of the spikes on the sides and the back of the head. As in the other diadectomorphs, the pineal “eye” was large. The teeth had become far fewer but were highly specialized, for the back teeth were broad, sharp chisels, evidently use- ful for chopping and cutting food. A particularly fine specimen is the almost complete skeleton of Hypsognathus (hips- Og-NATH-us), recently discovered near Passaic, New Jersey, and now in the Ameri- can Museum of Natural History.

With the passing of the procolophonids, during the late stages of Triassic history, the cotylosaurs became extinct. They had lived out their evolutionary life span—they had to give way to the more highly de- veloped reptiles of later Mesozoic times.

Such were the beginnings of the rentiles. Let us now follow their interesting evo]ution through its many ramifications.

A LARGE PARIASAUR, Scutosaurus, from the Permian beds of Russia, showing an early trend to giantism in the reptiles. This animal was as large as an ox and perhaps heavier, but it retained a primitive form. Notice the pro- portionately small head, the out-bowed legs, and the clumsy body

Restoration by John C. Germann

cere: on

oe fa 1a aise bate

PALEOZOIC

CRETACEOUS

TRIASSIC JURASSIC

PERMIAN

Turtles

Ancestral

birds

Thecodonts

Cotylosaurs, the stem reptiles

PENNSYLVANIAN

: Labyrinthodont amphibians

Saurischian dinosaurs

Pelycosaurs

/

The Mammal-like Reptiles

T MUST NOT BE THOUGHT that during the

early days of reptilian evolution in

Permian and Triassic times, the primi- tive anapsid reptiles, the cotylosaurians, had the world all to themselves. The laby- rinthodont amphibians presented a certain amount of competition to these early rep- tiles in the struggle for existence on the land, but the really serious antagonists of the anapsids were other reptiles, for this was the age when most of the great evolu- tionary lines of reptilian development were getting their start. The evolution of the reptiles was mushrooming out, so that there was a strong overlapping of the evolution- ary generations. Grandfathers and grand- children were living side by side.

One large division of the reptiles that arose, . developed, “and died out during the early phases « of reptilian life in the Permian and Triassic _ synapsids. These were the reptiles that, as shown by the drawings on page 49, were characterized by a lower opening in the skull roof behind the eye.

The history of the synapsids was, geo- logically speaking, of comparatively moder- ate length. The first of these reptiles made their appearance about 250 million years ago in Pennsylvanian times; the last of their kind had disappeared by the end of the Triassic period, 80 million years later. Nevertheless this is one of the most im- portant reptilian groups, because from cer-

tain branches of it there sprang the mam- mals, ae eek subsequent ly were destined to inherit the earth.

The synapsids were widely spread over

&& The family tree of the reptiles: a pic- torial diagram summarizing the history of the reptiles as discussed in the following pages

Restorations by John C. Germann

the face of the earth, for their remains are found on all of the major continents. Their evolutionary record, however, is confined for the most part to North and South America, eastern Europe, and South Africa. The subclass can be divided into two large

groups, the _Pelycosauria (pel-i-ko-sawr-

e-ya), found for the most part in the Upper Pennsylvanian and Lower Permian of North America, and the Therapsida (ther-Aps- i-da), mainly found in the Middle and Upper Permian and the Triassic of the Old World and South America.

Our knowledge of the pelycosaurs is de- rived mainly from fossils found in the Permian red beds of Texas. These fossils show that the pelycosaurs had their begin- nings as long, lizard-like reptiles, with rather sinuous bodies and sprawling limbs. (The term lizard-like is used here to con- vey a word picture. Such a term does not imply any relationship with or ancestry to the lizards, for it was to be many millions of years before the first lizards made their appearance on the earth.) Varanosaurus (var-AN-0-sawr-us) was a form typical of the primitive pelycosaurs. From such a begin- ning the pelycosaurs developed along several radiating evolutionary branches.

In Varanosaurus the

a a pattern for the pelycosaurs was set, that of elongated, sprawling-limbed, four-footed reptiles. Evolution in these animals was mainly a process of skull and backbone modifications.

basic structural

Some of the pelycosaurs grew large, and the skull deepened. They had numerous sharp teeth, the design, of which indicates that these were fish-eating animals, a sup-

53

Cynognathus

Moschops

XQ Dimetrodon

_ eile yNnee

Varanosaurus

A The evolution of the synapsid reptiles. As seen here, they showed wide variation in form, but their relation- ship is always indicated by the skull pattern shown on page 49

Restorations by John C. Germann

es a Te

position that is strengthened by the fact that these reptiles are found in stream de- posits together with the remains of fishes. Such was Ophiacodon (o-fee-a-ko-don)./ Certain pelycosaurs evolved tremen- dously long spines on the vertebrae, spines which in life must have supported a mem-

branous sail that ran down the middle of _

the back. These were the > sphenacodonts or finbacks, typified by the genus Dime n (dye-met-ro-don), a good-sized reptile, six or seven feet in length. Dimetrodon had a deep skull, armed with many cruel, dagger- like teeth. The sail on the back was tall, thrusting up two or three feet above the ‘line of the backbone.

What was the purpose of this huge sail, seemingly so cumbersome, and certainly a serious drain upon the blood supply and the energy of the animal? Much thought and discussion has been given to this problem, with suggestions ranging from the not-so- sublime to the downright ridiculous. Ac-

cording to one idea, the long spines on the vertebrae of Dimetrodon afforded a_ pro- tection for the spinal column—a_protection against the attacks of savage enemies. The only thing wrong with this theory is that there were no other large, active carnivo- rous reptiles at that time to prey upon Dimetrodon. Dimetrodon was the lord of his small universe, he was one of the largest and certainly one of the most active and predaceous of the animals living in Texas during Permian times. Another idea had it that the “sail” of Dimetrodon really was a sail, that this animal ventured out onto the surface of the Permian lakes and _ rivers, scudding along before the wind, tacking back and forth in a fashion approved in the best yachting circles. Such a theory is, of course, one on the ridiculous side.

Perhaps the truth is that the sail of Dimetrodon is not to be explained upon any functional grounds. It may very well be that this represents an unbalanced growth,

This grotesque “sail” has been a subject of much conjecture. Probably it is merely a case of hereditary maladjustment. In this Permian scene of over 200 million years ago, Edaphosaurus is fleeing from his flesh-eating relative Dimetrodon (in the background). Both were about five or six feet long

(=

“en

‘A fy) a y et

na

Restoration by John C, Germann

that it is an example of heredity “gone wild.” The ophiacodonts, for instance, had rather tall spines on the vertebrae, spines that served for the attachment of strong muscles to help hold up and stiffen the back. It may be that there was some sort of a hereditary upset, so that the spines elongated much faster than the animal grew, and since this strange adaptation was not particularly deleterious, the animal survived in spite of it. We frequently see such developments in nature.

For instance, there was a herbivorous pelycosaur, known as Edaphosaurus (e-DAF- o-sawr-us), in which the spines were not only elongated but equipped with numer- ous transverse processes, like the yardarms of an old square-rigger. It is certainly diffi- cult to assign any functional purpose to such a development. It is much more logical to assume that this peculiar growth was merely a case of a hereditary maladjust- ment.

The pelycosaurs are extraordinarily in- teresting to us, not only because of the bizarre adaptations shown by some of them, but also because some of these animals, particularly the sphenacodont-like forms, were _ the ancestors of those synapsid rep- tiles known as therapsids. The therapsids were the “mammal-like reptiles,” a descrip- tive term that delineates not only their general appearance but also their morpho- logical relationships, for these were the reptiles that were in part actually the direct ancestors of the Mammalia, that division of the animal kingdom of which we are members.

The therapsids are found in many locali- ties in the several continental areas, but it is in South Africa and in Russia that our evidence for the past history of these ani- mals is especially complete.

56°

The mammal-like reptiles had their be- ginnings in small synapsids known as dromasaurs, .from which they radiated through later Permian and Triassic times along two general lines of adaptation. One of these evolutionary lines followed a trend toward the development of bulk. The other line was one in which highly advanced and correlated structural features appeared, as will be shown below.

The large heavy therapsids appeared in the Permian and became dominant ele- ments in the animal assemblages of their day. These animals developed along two

are one known as the Dicynodontia (dye-stnE-o-dont-e-ya), the other as the Dinocephalia ~ (dye-no-sef-a-lee-ya). The dicynodonts were exceedingly numerous and rather varied. Some were compara- tively small, others were very large, as

The Permian reptile Moschops, as it might have appeared in South Africa some 200 mil- lion years ago. This animal typifies the large plant-eating Therapsids of South Africa

Restoration by John C, Germann =

bulky as present-day oxen. But all of them, whether large or small, seemingly were rather active, for these reptiles literally “got up on their legs,” the better to move across the land in which they lived. In short, these animals could walk with their feet underneath their bodies, so that the legs could be brought in for support against the constant downward pull of gravity. Perhaps the most striking feature of the dicynodonts was the specialization of the skull, for in these animals the head had undergone a profound transformation. The upper and lower jaws were beaklike in form. The teeth were usually lost, except in the males, which retained two enlarged

spikelike teeth in the upper jaw. The skull itself was modified so that the bones of its back portion formed a series of strong arches, probably as attachments for power- ful jaw muscles. Dicynodon was typical.

Although the preserved remains of dicynodonts are particularly abundant in South Africa, it is evident that these animals had a cosmopolitan distribution. Stahlekeria (stal-le-kER-e-ya) is a giant dicynodont found in Brazil; other dicynodonts are known from North America, China, and Europe.

The dinocephalians were rather similar to the dicynodonts in body form. They were large, powerful reptiles with strong limbs. The back sloped giraffe-fashion in typical members of the group, as for example in Moschops (Mos-kops).

“Considerable variety was shown in the adaptations of the head in these animals. Some of the more primitive forms, like Titanosuchus (tye-tan-o-sOoK-us), were carnivorous, with elongated faces and sharp, dagger-like teeth. Certain specialized

types, such as Moschops, were vegetarians, with rather weak jaws and peglike teeth. They all had very heavy thick skulls, and as a group were remarkable for the great development of the light receptor, the pineal organ or “eye” on the top of the head.

From our own anthropocentric viewpoint

all other reptiles pale into insignificance as compared with the theriodonts (THER-e-o- donts) and the ictidosaurs (ik-Tm-o-sawrs). These were the mammal-like reptiles par excellence, and as has already been said they were indeed the ancestors of our own blood kin, the mammals. y

The theriodonts, of which Cynognathus (sine-og-NATH-us) and Bauria (BowR-e-ya) were typical, were for the most part rather small or medium-size carnivorous reptiles, and like the other therapsids they had the body lifted up off the ground on strong legs —a sign that these were active animals. They had long, rather doglike skulls, which in their entirety show features directly antecedent to those of the warm-blooded, furry mammals. Thus in many of the theri- odonts there was a double ball-joint or condyle that accommodated the rotation of the head on the neck as in the mammals, whereas most of the reptiles have a single ball-joint. In the theriodonts there was a secondary palate as in the mammals, sepa- rating the nasal passage from the throat, a distinct advance over the typical reptilian conditions. In the theriodonts the bone in the lower jaw that bore the teeth was greatly enlarged, while the other bones were reduced—again an approach toward the mammalian condition. And correlative with this development there was a fore- shadowing of one of the most remarkable transformations in evolutionary history, the shifting of the two bones forming the joint

58

between the reptilian upper and lower jaws to form, surprisingly enough, two of the chain of three bones in the mammalian middle ear.

One of the most striking features in the skull of the theriodonts was the specializa- tion of the teeth. In most reptiles the teeth are all more or less alike, and they keep coming in during the life of the animal as fast as their predecessors are worn away or broken. In the theriodonts, however, there were some small front teeth, evidently for nipping and grasping, some large, broad back teeth, evidently for chewing or grind- ing, and between them some elongated, dagger-like teeth, evidently for slashing and tearing. Here we see an exact counter- part to the front incisors, the long, pointed canines, and the grinding teeth (the pre- molars and molars) of the mammals. More- over, there is every reason, from the evi- dence of the fossils, to think that the differ- entiated teeth in the theriodonts were di- rectly ancestral to the differentiated teeth of the mammals. Also, the evidence indi- cates that the manner of tooth succession in certain theriodont reptiles led finally to the condition typical of mammals, in which there are but two sets of teeth, milk or deciduous, and permanent.

It is not, however, the evidence in the skull and teeth alone that points to the di- rect descent of mammals from the theri- odont reptiles. For in these remarkable reptiles the vertebrae of the backbone, the shoulder blade, the hip bones, the limbs, and the feet all show many characteristics that clearly foreshadowed the typical mam- malian plan.

In the ictidosaurs the mammal-like spe- cializations are carried to such a high de- gree of development that it is a moot point whether these animals should be classified

as reptiles or as mammals. Certain features, such as the articulation of the jaws, indicate that by definition the ictidosaurs_are rep- tiles. But they are so close to the dividing line between reptiles and mammals that they are in effect intermediate between these two great vertebrate classes.

Such is a composite picture of a true “missing link,” one of the very important stages in the history of vertebrate evolu-

Vv A type of reptile that stood close to the ancestry of mammals: the flesh-eating therapsid reptile Cynognathus, an active and predaceous animal

Restoration by F. L. Jaques

tion, the link between the cold-blooded reptiles, which for so many millions of years were the undisputed rulers of the earth, and the warm-blooded mammals. which were destined to supplant them.

By the end of Triassic times the mam- mal-like reptiles, and more particularly the theriodonts and_ ictidosaurs, had gone through their course of evolutionary devel- opment and had become extinct. However, the mammals were not yet to take over domination of the earth from their rep- tilian ancestors. The first mammals, the de- scendants of the theriodonts, appeared in the Triassic, some 200 million years ago, but through the millions of years that consti- tuted the Jurassic and Cretaceous periods the descendants of these first mammals played a relatively insignificant part in the economy of life. The world still belonged to the reptiles; in fact, it was during the lush days of Jurassic and Cretaceous times that the reptiles rose to the greatest heights of their long history on this sphere. Those were the days of the dinosaurs, when there were giants on the earth.

39 |

Ancestors of the Dinosaurs

HE REIGN OF THE DINOSAURS was

founded some 200 million years ago

in Triassic times, the first division of the Mesozoic era. The last of the laby- rinthodont amphibians were seeking refuge in such streams and ponds as they could find, primitive turtles were continuing the history of the ancestral, roofed-skull rep- tiles, and the active, mammal-like reptiles were ranging across the land in search of their food. At that time the dinosaurs made their earliest appearance on the earth. Yet even though the lines of dinosaurian radia- tion became established in the Triassic pe- riod, the story of these great reptiles begins still further back in geologic time, in the distant days of the Permian, when the first diapsid reptiles made their debut on the stage of Earth History.

The 225-million-year-old records _ of Permian diapsids are rather scanty. _ Per- haps the best evidence as to the nature of these forerunners of a great line of evolu- tionary development is to be found in the little reptile, Youngina (young-EYE-na) or its close relative, Youngoides (young-oy-deez) from the upper Permian rocks of South Africa.

Youngina was small, and generally lizard- like in appearance. (Please remember that this is a comparison, and is not intended to suggest any relationships with the lizards, which appeared at a much later stage of geologic history.) Youngina had a long body and slender limbs. The head was pointed and the jaws were armed with sharp, needle-like teeth. The key to the rela- tionships of this animal is, of course, in the back portion of the skull, which had two

60

temporal openings, an upper one and a lower one, separated each from the other by bars of postorbital and squamosal bones. From an ancestry typified by reptiles such as Youngina the diapsids evolved in vari- ous directions during Mesozoic times, to become the dominant land animals of that great era of Earth History. The differentia- tion of the several lines of diapsid develop- ment was largely achieved during the Triassic period, and it was then that the

pse

The skull of a primitive diapsid reptile, Youngoides, from the Permian of South

Africa

Redrawn after Olson and Broom

most important diapsid stem was _ estab- lished. This was the order of reptiles known as the Thecodontia (theek-o-ponT-e-ya)— more commonly called the thecodonts—the ancestors of certain dominant Mesozoic reptilian groups, notably the dinosaurs, the flying reptiles, and the crocodilians.

The thecodonts had narrow, deep skulls, a trend of development that was fore- shadowed in Youngina and was well estab- lished in the early Triassic forms. In these reptiles there was an opening on either side of the skull, in front of the eye. This

opening, or fenestra, seemingly contributed = O - ——————

to the lightness of the skull, for in the thecodonts and their descendants the skull was in general light, yet strong and well braced.

In addition, the pineal opening or eye, so characteristic of the early reptiles, had disappeared. Finally, so far as skull char- acters are concerned, the thecodonts were typified by the limitation of the teeth to the edges of the upper and lower jaws; in other words, there were no teeth on the palate, as was so often the case among the more primitive Paleozoic reptiles.

It was, however, in the pose and the manner of progression that the thecodonts developed their greatest difference from all other reptiles. We have seen in the fore- going pages how the first land-living verte-

brates—the early tetrapods (rerr-ra-pods) evolved from certain fish, Steno dune the course of this evolution the four paired fins of the fish were transformed into four supporting limbs which enabled the animal to progress on land. Now in many of the reptiles the evolutionary specializations that have taken place have involved a strengthening or a modification of the four

S

The ancestors of the dinosaurs, the thecodonts, took to their hind legs and developed this special type of hip girdle

limbs, and there has been a retention of the four-footed method of walking. In the thecodonts, on the contrary, there was an early adaptation for two-footed locomotion. These animals rose up on their hind limbs. There was a division of labor between the two sets of limbs; the hind legs became

@, while

long and strong, for rapid running

the fore limbs became very much reduced and handlike, to be used for grasping. Such a profound change in the posture of these reptiles naturally was reflected in their bodily structure.

The body, instead of being supported fore and aft in the usual fashion, was “slung” at the hip joint, so that this joint became a sort of fulerum on which the movements of the entire animal were piv- oted. There was a long tail, to serve as a counterbalance for the body. The hip gir- dle or pelvis necessarily became strong, for it had to develop a long, stout articulation with the backbone as well as a deep socket to accommodate the ends of the upper leg bones. Therefore it became in the primitive diapsids a triradiate structure, serving ad- mirably as a strong connection between the body and the hind limbs,—to take the stresses and strains that are inherent in a partially upright pose.

Of the primitive thecodonts none were more characteristic than Euparkeria (yoo- park-rr-e-ya) from South Africa, or Orni- thosuchus (orn-i-tho-sook-us) or Saltopo- suchus (sal-to-po-soox-us) from Europe. When we look at one of these little reptiles, we see the ground plan for the dinosaurs. Let us therefore look at them carefully and remember them, for an understanding of this ground plan is the key to the under- standing of the dinosaurs. It is the blueprint to dinosaurian body form.

One group of thecodont reptiles became

61

FROM THIS SORT OF PATTERN, all of the varied dinosaurs developed: the skeleton of Saltoposuchus, a Triassic thecodont rep- tile only about four feet long

Modified from von Huene

specialized in an interesting manner. These were the reptiles known as the phytosaurs (FITE-0-sawrs), Which, like all thecodonts, lived in Triassic times. The phytosaurs are found in various parts of the earth, particu- larly in Europe, Asia, and North America. t Whereas the primitive thecodonts were small, the phytosaurs were rather large, ranging in size from six to 20 feet or more in length. And while the primitive theco- donts were mostly two-footed, the phyto- saurs were four-footed. It is perhaps sig- nificant, however, that even in these four- footed phytosaurs, the front limbs were noticeably smaller than the hind limbs. The return of the phytosaurs to the primi- tive four-footed mode of life was only one

phase of their adaptation, for these were .

semi-aquatic reptiles. They lived a croco- dile-like existence in the streams and lakes of the Triassic landscape, spending most of their time in the water, preying upon

| 62

such hapless animals as might come within their reach, and crawling out on the sandy bars and banks to sun themselves. The phytosaurs had a very crocodile-like ap- pearance, not only in the body but also in the head itself; indeed, to a casual eye, the skeleton of a phytosaur might easily be mistaken for one of a crocodile. The most noticeable difference is that in the phyto- saur the nostrils are located on the top of the head, immediately in front of the eyes, rather than at the tip of the snout as they are in the crocodiles. It should be empha- sized here that in spite of this similarity of appearance between the phytosaurs and the crocodiles, they were quite distinct groups of reptiles. The phytosaurs were not the ancestors of the crocodiles. i Here is a prime example of parallelism in evolution,—the similar development of distinct but related animals. The phytosaurs were like crocodiles, at a time when croco-

diles had not yet evolved. Perhaps it might be more accurate for this reason to say that the crocodiles are like phytosaurs; the phy- tosaurs came first and then died out—the crocodiles then appeared and evolved in a fashion that imitated to a remarkable de- gree the development of the phytosaurs. This parallelism between the phytosaurs and the crocodiles was due to the fact that both groups of reptiles occupied the same

“ecologic niche,” both groups played the same role in life history at the time in which they lived. In each case these were highly predaceous, water-loving reptiles that made their way in life by hunting. The phytosaurs, like the crocodiles of to- day, were the scourge of their environment. They feared nothing; they were the stealthy foes of whom all other animals of that day had to beware.

THE PHYTOSAURS resembled crocodiles but were not their an- cestors. They lived the same kind of life as crocodiles but did not survive beyond the end of the Triassic period, about 155 million years ago, before the crocodiles evolved in a parallel direction. Notice the nostrils immediately in front of the eyes. (Genus

Machaeroprosopus, from Arizona)

Restoration by John C. Germann

o

The Kinds of Dinosaurs

LL OF THIS TIME it has been our

purpose to get some idea of the

* course of reptilian evolution that went before the development of the dino- saurs, not only to give us a background for the proper understanding of dinosaurian but also because the Permo- Triassic history of the reptiles was in itself

evolution,

highly important in its bearing upon the later history of life on the earth.

In the last chapter we had a glimpse of the immediate diapsid ancestors of the di- nosaurs, how they developed, and in which directions their evolutionary progress led them. Now we are ready for the dinosaurs themselves.

As has been mentioned, the dinosaurs were diapsid reptiles, characterized by the two openings on each side of the skull be- hind the eye. Now it will probably come as a distinct surprise and perhaps a dis- appointment to the reader to learn that the word “dinosaur” does not denote a single and natural group of reptiles, but rather two quite distinct reptilian orders. Why then all this glib talk about “dinosaurs” if in using this term we are not utilizing a precise or definite name?

The explanation is relatively simple. In the first place, dinosaurs were virtually un- known only a little more than a hundred years ago. When first the bones of these animals were studied by scientists in Eng- land and in Europe, there was no term to indicate them collectively. Then in 1842 the great English paleontologist and anatomist, Sir Richard Owen, invented the name Dinosauria, from the Greek deinos, “terrible” and sauros, “lizard,” to apply to

64

the remains of large land-living reptiles found in rocks of Mesozoic age. Only later did it become apparent that the dinosaurs belonged to two quite distinct orders of reptiles, as distinct from each other as, for instance, cattle and horses. So the term “dinosaur” assumed a general rather than an exact meaning. Even so, it remains a useful name. It indicates a large category of prehistoric beasts, but it is a “loose” term. It may be compared with “hoofed animals” or “ungulates,” the suitable term used when we wish to speak about our modern cattle and horses in one breath.

Two great orders of reptiles made up the dinosaurs. These were the “Saurischia” and the “Ornithischia,” names which mean merely “reptile hips” and “bird hips.” The Saurischia (sawr-1ss-kee-ya) were those di- nosaurs having the three bones of the hip arranged more or less according to the typi- cal reptilian plan, while the Ornithischia (orn-ith-1ss-kee-ya) were those dinosaurs in which the bones of the hip resembled in their arrangement the pelvis of birds.

This is the primary, fundamental division of the dinosaurs, extending back to the be- ginnings of dinosaurian history. All of the dinosaurs had a common ancestry, in that they were all descended from certain theco- dont reptiles. But once the separation be- tween the saurischians and ornithischians was established—and that came about dur- ing Triassic days—these two groups of reptiles remained quite distinct from each other.

It is this structural plan of the pelvis and of other parts of the skeleton as well that distinguishes the two orders of dinosaurs—

no other standard will suffice. For instance, it is a common misconception to suppose that dinosaurs were all huge reptiles, carry- ing their heads high in the clouds, and borne on stout legs having the general di- mensions of small redwood trees. Nothing could be more erroneous. Some of the di- nosaurs were large, but others were very small. Indeed, there are some dinosaur skeletons that are hardly more than a foot in length; others are no larger than rabbits or turkeys. But given the structural pattern, the pattern that was established in the Triassic thecodonts, the saurischian and

ornithischian dinosaurs can all be ade- quately defined and the picture of dino- saurian evolution limned. This picture in simplified form is given in the chart on the

following page.

It is a picture in which we see the perfec- tion and modification of the basic thecodont plan, the plan which had for its foundation a two-footed posture, a deep, light skull, and a carnivorous diet, with all of the im- plications of hunting and rapid movement imposed by such a diet and by such a mode of life.

Two trends are to be seen in the develop- ment of saurischian and ornithischian adap- tations from a thecodont ancestry. One of these was the general trend towards an increase in size. The ancestral thecodonts were small reptiles; many of the later dino- saurs were comparatively large—though this is not invariably the case. The other was the trend towards a modification of the

CRETACEOUS

JURASSIC

TRIASSIC

ORNITHOPODS (Duck-billed Dinosaurs) Herbivorous, both two-footed and four-footed forms, generally living in the water along river and lake shores

CERATOPSIANS (Horned Dinosaurs) Herbivorous, four-footed dinosaurs with horns on the head

ANKYLOSAURS (Armored Dinosaurs) Herbivorous, four-footed, armored animals

STEGOSAURS (Plated Dinosaurs) Herbivorous, four-footed armored types

DINOS SAUROPODS (Giant Dinosaurs)

eran AURs Herbivorous dinosaurs that a generally walked on all fours; oO the giants of the dinosaur world

<pURISCHI4,y Dn

Sg A SIMPLIFIED FAMILY TREE %,. OF THE DINOSAURS

The two-footed ancestors of all the

dinosaurs, the Thecodontia, gave

rise to two main orders of dinosaurs

and six suborders, as shown above

THECODONTIA Ancestors of all dinosaurs

THEROPODS (Carnivorous Dinosaurs) Primarily flesh-eaters that walked on hind legs and used front limbs for grasping

primitive or ancestral, two-legged posture —a very marked trend in the dinosaurs. Only in the persistently carnivorous thero- pods was the purely two-footed pose of the thecodonts retained. In all of the other saurischians and ornithischians there was a definite drifting away from the ancestral carnivorous mode of life, and from the bi- pedal pose. The sauropods and most of the ornithischian dinosaurs became large plant- eaters. A big bulky animal would be at an obvious disadvantage in attempting to carry himself about on two legs; consequently these dinosaurs came down on all fours. But it must be remembered that this was a secondary return to the primary four-footed pose, and this can be seen because the front

TWO-FOOTED

FOUR-FOOTED

S 7 The small theropod dinosaur Ornitholestes, represented in the act of catching the first known bird, Archaeopteryx. Its food probably consisted mostly, however, of other small reptiles, eggs, insects, and the like. Ornitholestes preserved many of the features of the ancestral dinosaurs. From animals similar to this the great carnivores and sauro-

pods evolved Restoration by Charles R. Knight

legs of even the most completely four- footed of these animals were almost always noticeably the smaller. The heritage of the ancestor was retained in the descendant.

Saurischia

Theropoda (The carnivores)

The theropods (THER-o-pods) preserved more completely than any of the other di- nosaurs the primitive characteristics of their thecodont heritage. They remained the true two-leggers, and for the most part they were flesh-eaters.

In such persistently small animals as the Jurassic Ornitholestes (orn-i-tho-LEs-teez) we see a general retention of ancestral di- nosaurian features. Ornitholestes was no more than five or six feet in length—and this includes the long, attenuated tail which served as a lever to balance the weight of the body. All in all this was a remarkably light and graceful little dinosaur, with strong, birdlike hind limbs, on which it could probably run through the dense tropi- cal greenery with considerable swiftness and agility, darting in and out in search of its prey. The front limbs of Ornitholestes were relatively small as in all the theropods, and there were long, grasping fingers with which this little animal could hold its food. The skull, too, was small and light, deep and narrow, and armed with sharp teeth well adapted to biting and tearing. On the whole this was an efficient little mechanism for the catching of Jurassic small fry, and thus Ornitholestes fulfilled his role in the ecological or environmental scene of that day. This was the seeker of small game, of other ground-living reptiles that hid in the shelter of rock crannies or climbed up the stems of ferns.

A decided contrast to this graceful little

68

dinosaur was his giant contemporary, the huge theropod known as Allosaurus (al-lo- SAWR-us), one of the mighty hunters of the Jurassic, an animal some 35 feet in length that swung across the landscape in majestic and awful splendor. In a sense Allosaurus was an enlarged edition of his little relative, Ornitholestes, for this giant was a two- legged meat-eater. But giantism in nature is more than a simple process of something little being reproduced on a large scale, for with size there come many mechanical problems of weight and accompanying stresses and strains, so that the big animal shows many changes in proportion and many differences in structure as compared with the little animal.

Thus Allosaurus had relatively very heavy, strong hind limbs, to carry its great weight. And as a corollary to the strains consequent upon size, the entire pelvis in this animal had become strong and heavy for the attachment of the powerful muscles that moved the hind legs.

The hands of this great meat-eater were armed with hooklike claws, a development in keeping with the size and the violent mode of life which this hunter must have led. Perhaps the greatest difference to be noted between the small carnivore and the large carnivore is to be seen in the huge head that was carried by the giant Allo- saurus. Here was a large skull which in spite of its size was remarkably light and strong, and possessed a widely gaping mouth armed with dagger-like teeth. This was the business end of the beast. Allo- saurus was the hunter of big game, and as such he must needs be provided with weap- ons sufficient for the task—that is, with large, strong jaws and heavy, sharp teeth. He had them.

The culmination of development in the

— a ee OE ee ee SS eae

a

A Allosaurus, a large predaceous theropod dinosaur of Jurassic age. It is represented here as devour- ing the carcass of a brontosaur, one of the large dinosaurs on which it probably preyed

Y The largest carnivorous land animal that ever lived: Tyrannosaurus. This animal represents the culmination of meat-eating adaptations in the dinosaurs. It evidently preyed upon some of the large herbivorous dinosaurs of its day and is here represented as attacking the horned

dinosaur, Triceratops Restorations by Charles R. Knight

theropod dinosaurs was attained by the giant Cretaceous form, Tyrannosaurus (tye- ran-0-sAWr-us ), the “king of the dinosaurs.” This was the greatest and most fearful Jand- living carnivore that has ever dwelt on earth, an animal of magnificent proportions and terrible power, beside which the mod- ern lion and bear would appear as almost harmless dwarfs. Tyrannosaurus, standing on his powerful hind limbs, carried his head some 18 or 20 feet above the ground, while the distance from the tip of his nose to the tip of his tail was all of 50 feet. This animal might have weighed some eight or ten tons when he was a living creature of destruc- tion.

The several specializations which charac- terized the upper Jurassic Allosaurus were carried to extremes of development in the Cretaceous Tyrannosaurus. Thus, this giant among the carnivores had exceptionally strong legs and a very stout pelvis to serve as a fulcrum between the backbone and the limbs. In Tyrannosaurus there was a reduc- tion of the fore limbs so that they had be- come inordinately small. Correlative with this reduction of the forelimbs there was also a reduction in the hands, which were armed with hooked claws. The reduction affected not only the size but also the num- ber of digits, so that only two claws were functional on each hand; evidently Tyran- nosaurus had little use for his arms.

That this was so is proved by the ex- tremes to which the head developed in this great dinosaur. The skull of Tyrannosaurus was indeed a tremendous structure, power- fully built, with a mouth having a gape of almost unprecedented size and armed with huge, scimitar-like teeth. Such was the of- fensive weapon for this mighty hunter, a weapon that could be used with effect against other large and tough dinosaurs of that day.

70

There were other carnivorous theropods living in Cretaceous times, similar to Tyran- nosaurus but showing lesser degrees of spe- cialization. One of these was the somewhat smaller form, -Gorgosaurus (gor-go-SAWR- us).

A somewhat different line of theropod specialization is to be seen in the Creta- ceous dinosaur, Struthiomimus (strooth-ee- O-MIME-us), the “ostrich dinosaur.” This evolutionary line, alone among the thero- pods, departed from the carnivorous mode of life and turned to a vegetarian or perhaps a fruit-eating life. ~ Struthiomimus was a dinosaur of medium size, and like the other theropods was bi- pedal, with a long tail to act as a counter- balance to the body. The fore limbs were rather well developed and were provided with long-fingered, grasping hands, some- thing on the order of the hands in Ornitho- lestes.

It is in the structure of the head and neck that the “ostrich dinosaur” shows the greatest departure from the typical thero- pod adaptations. In this reptile the neck was very long, sinuous, and _ birdlike, as compared with the rather medium-length or even short neck of most of the theropods, while the head was small, and lightly built. The skull in Struthiomimus was remarkable not only for its small size and light construc- tion, but also because of the fact that all of the teeth had been lost, while the jaws were beaklike—again an ostrich-like adap- tation. It would seem that Struthiomimus lived a harmless and blameless life, eating such fruits or buds or insects that might come its way, with ever a wary eye cocked on the big rapacious carnivores that ranged across the Cretaceous landscape.

Sauropoda

The sauropods (sAwr-o-pods) were the

'

A The Upper Cretaceous theropod, Struthiomimus. This dinosaur had gotten away from the active carnivorous habits of its theropod predecessors and become birdlike. The jaws developed as a flat

horny beak that might be useful in eating fruits, other green things, insects, and small reptiles

Restoration by Erwin S. Christman

Vv One of the largest dinosaurs, Brontosaurus, a creature some 80 feet long and 40 tons in weight. It inhabited the marshes and streams of western North America between 120 and 155 million years ago and fed upon green plants in its tropical environment

Restoration by Charles R. Knight

——

Byres

* 77

giants of the dinosaurian world and, so far as land-living animals go, the giants of all time. No other land animals have reached the great bulk attained by some of the sauropod dinosaurs, and only the huge whales in the sea have exceeded them.

The beginnings of sauropod history may be seen well exemplified by the Triassic dinosaur Plateosaurus (plat-e-o-SAwR-us), found in Europe and Asia. This was a dinosaur of medium size, some 20 feet in length. It was characterized by its long tail and by its rather long neck, surmounted by a comparatively small head. Plateosaurus had, of course, the typical three-pronged or triradiate pelvis of the saurischians, and like its theropod relatives it was at least partially bipedal. In Plateosaurus there was some enlargement of the fore limbs, which suggests that while this dinosaur may have tramped across the Triassic landscape on its strong hind limbs, it was nevertheless quite capable of assuming a four-footed posture for the purpose of feeding. The teeth were no longer the sharp blades so typical of the meat-eating theropods; rather they showed a sort of flattening, and a blunting of their points, as if they were becoming adapted to the cropping and cutting of green, leafy plants.

It was in the Jurassic that the sauropod dinosaurs reached the culmination of their evolutionary history. This was the period of the giants, of Brontosaurus (bront-o- SAWR-us), Camarasaurus (kam-ar-a-SAWR- us), and Diplodocus (dip-Lan-do-kus) in North America, of Cetiosaurus (seet-ee-o- sAwR-us) in Europe, and of the huge Brachiosaurus (brak-e-o-sAwr-us) in Africa. Brontosaurus is a typical sauropod and il- lustrates very well the characters of the group.

This dinosaur was a tremendously long

| 72

animal, some 70 or 80 feet in length from the nostrils to the tip of the tail, and like all of the typical sauropods it walked on all fours. Much of the length of Bronto- saurus was taken up by the long tail, which at its end was attenuated and whiplike, and by the correspondingly long neck. Even so, the body was a huge, bulky affair weighing in itself many tons, supported by great,

postlike legs. As in almost all of the four-_

footed dinosaurs, the hind limbs were much larger and more massive than the front limbs, since as already menticned the four- footed pose in these animals was a second ary development. The feet of Brontosaurus were short and broad, as would be neces- sary to support an animal of such bulk, and they were armed with curved claws—one on each of the fore feet and three on each of the hind feet.

The head of this great reptile was re-

markably small compared to the body, and it is difficult to imagine how an animal of such size could take in through such a modestly-proportioned mouth enough green stuff to keep it alive. Yet there is no doubt but that Brontosaurus was a plant feeder, and like all plant-eating animals it had to consume a great amount of bulky material in order to get sufficient nourishment to keep it alive and reasonably active. It must be remembered, of course, that these great reptiles must have been rather sluggish, as are the modern cold-blooded vertebrates, so that they would not require as much food to satisfy their needs as we might think would be necessary. At any rate, we know that Brontosaurus did live and pros- per over a long period of geologic time, so evidently he found his small mouth suff- cient for his purposes.

All of the other sauropods represent varia- tions of the pattern seen in Brontosaurus.

One well-known form from North America, Diplodocus, was remarkably long and ta- pering, although not so bulky as his cousin, Brontosaurus. In this animal the skull was even smaller than in Brontosaurus, while the teeth were weak pegs, no bigger in diameter than lead pencils. The nostrils of Diplodocus were located on the top of the head, an adaptation for life in the water. In- deed, the evidence would seem to indicate that all of the sauropods spent much of their time in the water, wading around in swamps, and even venturing out into the deeper reaches of lakes or rivers to escape from danger.

The largest of all’ the sauropods was Brachiosaurus which is found on opposite sides of the world, in North America and in east Africa. This dinosaur was not so long as Brontosaurus or Diplodocus but it was very bulky. In Brachiosaurus there was a strange enlargement of the front part of the body, so that the fore limbs were larger than the hind limbs (an exception to the general rule), while the neck was very long and heavy. This caused the back to slope giraffe-fashion to the hind limbs, while the tail was comparatively short. Brachiosaurus had the nostrils raised on a sort of dome or eminence on the top of the head, an indication, along with the long neck and raised fore-quarters, that this dinosaur probably waded along the bottom in deep water, where it was enabled by its great size to thrust the top of the head above the surface, periscope fashion, to breathe and to survey the surroundings.

| Ornithischia Ornithopoda

The ornithischian dinosaurs were on the whole more highly evolved than were the

saurischian forms. This is a fundamental truth which has its foundations in the basic, diagnostic characters of these two great groups of dinosaurs. It will be remembered that the saurischians were the forms with an essentially triradiate arrangement of the

pelvic bones, similar to the arrangement in the ancestral thecodont reptiles, while the ornithischians were those animals in which there was a rotation of the pubic bone so that it came to occupy a position parallel to the ischium. This formation of the pelvis is in itself an indication of the advanced position of the ornithischians as compared with the saurischians.

The argument extends to other parts of the body as well. In particular the or- nithischian dinosaurs showed specializa- tions of the head and of the teeth, which went far beyond the specializations to be seen in their more conservative saurischian cousins. It is interesting, too, to see that the Saurischia had gone through the major phases of their evolutionary development during Jurassic times, so that the saurischi- ans of the ensuing Cretaceous period were for the most part continuations of “Jurassic patterns.” The Ornithischia, on the other hand, experienced by far the major part of their evolutionary development in Creta- ceous times.

The least “advanced” of the ornithischian dinosaurs are to be found among the large group known as the Ornithopoda (orn-i- THO-pod-a), the duck-billed dinosaurs and their relatives. This is not to say that all ornithopods (orN-i-tho-pods) were of a par- ticularly primitive aspect—indeed, in some of the Cretaceous forms we see highly spe- cialized types. But there was one group of the ornithopods that was relatively unspe- cialized—the group known as the campto- saurs.

73 |

A Camptosaurus: One of the first of the ornithischian dinosaurs, which lived in late Jurassic and early Cre- taceous times. All of the later ar-

mored dinosaurs, duck-bills, and horned forms were derived from an- cestors something like this five- to eight-foot plant-eating dinosaur

The camptosaurs or iguanodonts ap- peared about 140 million years ago in the Jurassic period, and they continued their development through Lower Cretaceous times. These dinosaurs were bipedal, al- though it is an interesting fact that the camptosaurs did not lead a completely two- footed ambulatory existence as did the carnivorous theropods. For the camptosaurs were perfectly capable of coming down on all fours whenever the occasion demanded such a pose, which was probably quite often the case.

In Camptosaurus (kamp-to-sAwr-us) the skull was rather long and low, with flat- tened, bladelike teeth—obviously intended for the cutting and chewing of green plants. In these animals there were no teeth in the front of the mouth, either above or below— a basic pattern that was repeated in virtu- ally all of the ornithischian dinosaurs. In- stead, the front of the jaws formed a bird- like beak, which in life was obviously cov- ered by a horny sheath and served as an efficient mechanism for the biting and cut- ting of plant food. It should be repeated here that all of the ornithischians were strictly herbivorous. ~

One of the very interesting dinosaurs, which unfortunately is not to be found in any of the American museums, is the Euro- pean ornithopod, Iguanodon (i-cwan-o- don). Iguanodon, a close relative of Camp- tosaurus, is of particular interest not only because it is a well-known animal of which numerous complete skeletons have heen discovered, but also because it was the first dinosaur to be scientifically described.

€& Trachodon, a duck-billed dinosaur of late Cre- taceous times. The duck-bills were all aquatic and spent much of their time either in or near the water

Restorations by Charles R. Knight

In 1822 some peculiar teeth were found in Lower Cretaceous rocks in the county of Sussex, England, by the wife of Dr. Gideon Mantell, a famous English paleontologist. Of course nobody at that time had ever heard of a dinosaur, in fact the name “di- nosaur’ had not yet been invented, so it was indeed a puzzle as to what the strange teeth found by Mrs. Mantell might be. Mantell, unable to identify the teeth to his satisfaction, sought the advice of Sir Charles Lyell, who in turn submitted the specimens to Baron Georges Cuvier, the celebrated French anatomist. Cuvier, after due delib- eration, announced that these teeth be- longed to a rhinoceros.

That didn’t seem right, so Mantell went back to look for more remains, and found some bones in the quarry where the original discovery was made. There was some more guessing by Cuvier—this time he voted in favor of a hippopotamus—but finally, after diligent comparisons, Mantell himself finally came to the conclusion that here was a new type of reptile, of large size, and with teeth like those of the present-day iguana. Hence the name, Iguanodon.

At first Iguanodon was restored as a four-footed reptile, but in later years an unusual series of seventeen skeletons was found in a coal mine in Belgium, and the true nature of this dinosaur was recognized.

The ornithopods reached the height of their development in the Cretaceous hadro- saurs or trachodonts, often called the “duck- billed” dinosaurs. These were large dino- saurs, partially bipedal and __ partially quadrupedal, and they were obviously water-loving animals. This is shown by the structure of the head, in which the front of the skull and jaw were broadened into a flat “duck bill” (hence the sobriquet) that was most assuredly very handy for grovel-

75

Kritosaurus

An expansion of the nasal bones gave Kritosaurus a beaked or hook-nosed appearance

Pe LT Ne te,

Bie . eee miss

Corythosaurus

A large crest, involving the premaxillaries as well as the nasal bones, distinguished Corythosaurus. The long S-shaped curve of the nasal passages formed within the crest an air storage chamber permitting the animal to remain under water longer

\

Lambeosaurus

The crest projected behind the skull in Lambeosaurus, in addition to forming a sort of hatchet-shaped blade on the top of the skull

Parasaurolophus

In Parasaurolophus the crest, still formed of the nasal and premaxillary bones, reached the extreme develop- ment. In this crest, the greatly elongated nasal passage formed an air storage chamber of considerable dimensions

Restorations by John C. Germann

ing in the shallow water and muddy bot- toms of streams and ponds. It is also shown by webbing between the toes, revealed in several cases where skin impressions of these animals have been preserved.

The central type is Hadrosaurus (had-ro- saAwR-us) or Trachodon (TRAK-o-don), found in various parts of western North America and in the eastern portion of the continent, too. Indeed, as already mentioned the first dinosaur skeleton to be found and described in North America was a Hadrosaurus skele- ton, discovered not in the wilds of the west- ern badlands, but in the town of Haddon- field, New Jersey, a suburb of Philadelphia. A glance will show that Trachodon was a camptosaur grown large, in which the skull was flattened, especially in front, to form the broad “duck bill” so characteristic of these dinosaurs.

In late Cretaceous times there were nu- merous evolutionary variants of this central hadrosaurian theme, developments charac- terized for the most part by peculiar and bizarre modifications of the skull. One of these was Kritosaurus (kritt-o-sAwR-us). An- other was Corythosaurus (kor-ith-o-sAwr- us). Another was Lambeosaurus (lamb-e-o- sAwr-us). Another was Parasaurolophus (par-a-sawr-AH-lof-us).

Suffice it at this point to note the strange and wonderful lengths to which evolution carried these fascinating dinosaurs. On page 87 we refer further to the significance of the peculiar skull structure of the several types of hadrosaurian dinosaurs.

A very peculiar group of ornithopod di- nosaurs was that of the troddonts (TRO-0- dahnts), small to medium-size dinosaurs, in which the body seemingly was rather simi- lar to the body of other ornithopods, but in which the head was remarkably special- ized. In these dinosaurs the roofing bones of

76

the skull became extraordinarily thick, so that there was a dome of solid bone above the brain, while on the nose and at the back of the head there was a fearsome ar- ray of nodes, points, and spikes. The ex- treme was reached in one of the late Creta- ceous troddonts, Pachycephalosaurus%pak- e-SEF-a-lo-sawr-us), having a solid domed skull roof some nine inches thick. This was, indeed, the original bonehead!

Stegosauria

There were two groups of ornithischian dinosaurs which during the course of their development were distinguished by a “hands off’ trend of evolution. These were the so-called armored dinosaurs, the walk- ing fortresses that defied their enemies by the comparative impregnability of their defense—the stegosaurs of the Jurassic

and the ankylosaurs of the Cretaceous.

Stegosaurus (steg-o-SAWR-us) was typical of the Jurassic pattern of dinosaurian armor. Here was a rather large ornithischian, com- pletely quadrupedal, but with the fore limbs so much smaller than the hind legs that this animal was a congenital “high- behind.” From the tiny camptosaur-like head, carried rather close to the ground, the back arched in a steep curve to the high hips, and then descended again to the tip of the tail. The massive body was supported by strong legs, ending in broad padded feet.

The “armor” of Stegosaurus was perhaps the most striking feature of this strange dinosaur, and it contributed much to the strange appearance of the beast. Down the middle of the back there was a series of upright, triangular plates, arranged alter- nately, while the tip of the tail bore four

Stegosaurus, an armored dinosaur of the Jurassic period. Some of the earlier restorations showed this animal with the plates paired, and with six tail-spikes, but the arrangement of alternating plates with four spikes on the tail, shown here, is based upon the most recent evidence

Restoration by Charles R. Knight, copyright The Chicago Natural History Museum

huge spikes, presumably intended to serve as a pointed reminder to any other dinosaur that might venture closer than was con- sidered proper by Mr. Stegosaurus.

Whether the plates along the back served as a really effective protection to the spinal column is a question which at this distant date cannot be very satisfactorily answered. At least they were decorative.

This dinosaur is famous, among other things, for the small size of his brain. In- deed, this was a peanut-headed reptile, if ever there was one,—an animal bigger than an elephant, with a brain about the size of a walnut. It is a remarkable fact that the brain of Stegosaurus was actually 20 times smaller than the enlargement of the spinal cord in the hip, which served to control the movements of the heavy hind limbs and the powerful tail. Which has given rise to the quaint, and somewhat fanciful story that this dinosaur had two sets of brains—an idea charmingly perpetuated by the late Bert Leston Taylor, a columnist on the Chi- cago Tribune.

THE DINOSAUR

“Behold the mighty dinosaur, Famous in prehistoric lore,

Not only for his power and strength But for his intellectual length.

You will observe by these remains The creature had two sets of brains— One in his head (the usual place), The other at his spinal base. Thus he could reason “A priori’ As well as ‘A posteriori.’ No problem bothered him a bit He made both head and tail of it.

“So wise was he, so wise and solemn, Each thought filled just a spinal column.

If one brain found the pressure strong It passed a few ideas along.

If something slipped his forward mind "Twas rescued by the one behind.

And if in error he was caught He had a saving afterthought.

As he thought twice before he spoke He had no judgment to revoke.

Thus he could think without congestion Upon both sides of every question.

Oh, gaze upon this model beast, Defunct ten million years at least.”

—BeErRT LESTON TAYLOR

It wasn’t quite as bad as all that, but at any rate Stegosaurus must have been pretty much a walking automaton, without much of what might be called original thought.

Ankylosauria

The Cretaceous armored dinosaurs were the ankylosaurs, somewhat less startling in appearance than the stegosaurs but perhaps somewhat more effectively protected. These

ORNATE ARMOR helped to protect Palaeoscincus (center foreground) from other dino- saurs of his time. To the left is Trachodon, to the right (middle distance) Corythosaurus and (farther away) Parasaurolophus. In the center background are two Struthiomimus

Restoration by Charles R. Knight, copyright The Chicago Natural History Museum

THE FIRST OF THE HORNED DINOSAURS, Protoceratops, from theY Cretaceous of Mongolia. In this primitive member of the group the horns were as yet undeveloped

Restoration by Charles R. Knight, copyright The Chicago Natural History Museum

dinosaurs had a real armor plating, an over- lapping pavement of bony plates presum- ably covered with horny sheaths, which en- cased the entire body, head and tail, arma- dillo-fashion.

Ankylosaurus (an-kyle-o-sAwr-us) typical of this group of dinosaurs. A me- dium-size dinosaur this was, quadrupedal in pose and of heavy build. The skull was broad and strongly protected by the armor plates, while the arched back was com- pletely encased by the articulating scutes. Add to this a heavy, stiff tail, ending in a huge clublike mass of bone and you have a picture of Ankylosaurus.

Here was the tank of Cretaceous days, low, squat, and strongly protected by his outer casing. He could blunder along through the world without a great deal of concern about the rapacious carnivores that

Was

ranged far and wide, the gigantic Tyran- nosaurus and his lesser relatives. By seeking refuge within the strength of his shell he was fairly safe from attack, and with the knout on the end of his tail he might lay about him, to create devastation within the arc swept by that mighty club.

Most of the other armored dinosaurs of the Cretaceous were generally similar to Ankylosaurus. Of these, *Palaeoscincus

‘(pale-e-o-skink-us) and Nodosaurus (node-

0-SAWR-us) may be mentioned.

Gj eratopsia

Of all the dinosaurs the Ceratopsia (ser- a-Tops-e-ya) or horned ornithischians were the last to appear. The earliest ceratopsians appear in beds of Cretaceous age, and in the relatively short lapse of geologic time between their rise and their final extinction

these animals enjoyed a remarkably varied course of evolutionary adaptation.

The ancestry of the ceratopsians is indi- cated, if not actually represented, by a small bipedal dinosaur from the Lower Cretace- ous of Mongolia, known as Psittacosaurus (sit-a-ko-sawr-us). This little animal was characterized especially by the develop- ment of its skull, which was very deep and narrow, so that the front of it formed a large pointed beak, similar to the beak so charac- teristic of the horned dinosaurs. Indeed, Psittacosaurus, as has been shown by Greg- ory, is an almost ideal ancestor for the cera- topsians, not only with regard to the devel- opment of the skull but also because of the characteristic expression of the pelvis, in which the pubic bone was reduced (a typi- cal ceratopsian feature), and because of the form of the limbs and of the feet. A series running from Psittacosaurus to Protocer- atops~ (prot-o-sER-at-ops) (the first of the “frilled” ceratopsians), and to the later forms, shows how the small two-legged dinosaurs became specialized to give rise to the giant horned dinosaurs of Upper Cre- taceous times.

| The first of the frilled ceratopsians was

a small dinosaur known as Protoceratops, discovered a few years ago in the upper Cretaceous Djadochta beds of Mongolia. This little ornithischian was five or six feet in length, and in spite of its comparatively small size it would seem to have been al- most entirely quadrupedal. Evidently the four-footed pose was established at a very early stage in this line of dinosaurian de- velopment.

The most striking feature of Protocera- tops was its head, which was relatively very large and deep. The front of the muzzle and the jaws formed a hooked parrot-like beak, and the back of the skull extended back to

80

form a pierced or fenestrated frill that over- hung the neck and the shoulder region. Like the other ornithischians, Protoceratops lacked teeth in the front of the jaws, except for two tiny vestigial teeth on each side near the front of the upper jaws—obviously an evolutionary “hang-over” from a more primitive stage of development. This little animal, although a horned dinosaur, had only the beginnings of a nasal horn, for he was the first of his line and had not devel- oped the specializations that were so char- acteristic of his large and impressive grand- children.

Protoceratops is known from a number of skeletons and from a remarkable series of skulls which show the development of this animal from a newly hatched baby to a fully developed adult. These skulls show, for instance that the flat “frill” at the back of the skull was not present in the newly born Protoceratops, but that it grew as the animal grew up, so that by the time adult- hood was attained, there was a well-devel- oped, fully-formed frill. Incidentally, it is probable that this frill grew as an accom- modation for strong neck muscles which controlled the movements of the head, these in turn being made necessary by the great relative increase in the size of the skull.

To make our knowledge of Protoceratops really complete, there were discovered with this little dinosaur several nests of its eggs. These were the first dinosaur eggs to be discovered, and as such they became very famous in the public press some years ago. The eggs are similar in shape and in surface texture to the eggs of certain modern tur- tles. In two of them were found the bones of an unhatched embryo Protoceratops!

From the modest beginnings of Protocer- atops, the giant horned dinosaurs of late Cretaceous times evolved. Of the great

A.M.N.H. photograph

A nest of eggs of Protoceratops, the ancestral horned dinosaur, as they were dis- covered in Mongolia by the Central Asiatic Expedition of the American Museum of

Natural History

ceratopsians, Triceratops (try-SER-at-ops) is typical and is perhaps the best known

genus. This was an animal about 20 to 30 feet

in length, standing some eight feet in height

at the hips. Needless to say, Triceratops was fully quadrupedal, with strong limbs, and short, broad feet. The remarkable feature of Triceratops and of all the large horned dinosaurs was the enormous head, constitut-

The last of the horned dinosaurs: Triceratops, a strong animal, admirably equipped 9

for defensive fighting. The seven-foot skull with its flaring “collar” was fully one-

third the entire length of the animal. From the Upper Cretaceous of North America Restoration by Charles R. Knight, copyright The Chicago Natural History Museum

Restorations by John C, Germann

ADAPTATIONS IN THE HEAD OF THE HORNED DINOSAURS

Ee

MONOCLONIUS

From the ancestral type below evolved the first of the “frilled” ceratopsians, Protoceratops. Evolution in the late horned dinosaurs, as shown above, was marked by varying adap-

PROTOCERATOPS tations in the horns and frill

The probable ancestral type 7 is indicated by the small S&

genus PSITTACOSAURUS PSITTACOSAURUS

ing fully one-third of the entire length of the animal—an accentuation of a develop- ment that was already apparent in Proto- ceratops. Thus, in a large Triceratops the skull was some seven feet in length, of which about one-half was occupied by the great flaring frill that extended back over the neck and shoulders. As in all of the other ceratopsians, the skull and jaws were deepened and narrowed in front to form a hooked parrot-like beak. This animal car- ried on its nose a stout horn, and over the eyes were two other horns, these latter very long and strong and admirably suited for defensive fighting.

The skull of Triceratops was attached to the backbone by a ball-and-socket joint at the back of the brain case, which was at about the middle point of the skull, beneath the front of the frill, so that the skull was virtually balanced upon it. With tremen- dous neck muscles attached to the bottom of the frill, combined with strong leg mus- cles, Triceratops must have had a remark- able ability for making short powerful lunges with the head down and the two long horns directed forward to impale any luckless antagonist. Such an arrangement

was eminently useful to Triceratops, for he lived in a land inhabited by Tyrannosaurus, than whom there never was in this world a more powerful adversary.

The other giant ceratopsians of late Cre- taceous days were variations on the Tricer- atops theme. Their differences were ex- pressed mainly in the development of the horns and the frill.

Thus there was Chasmosaurus (kas-mo- SAWR-us), with smail horns. And Mono- clonius (mon-0-KLON-e-us) with a large horn on the nose and small horns over the eyes. And Styracosaurus (sty-rak-o-sAwr-us) with a large horn on the nose, no horns of conse- quence above the eyes, but spikes all around the margin of the frill.

These were the last of the dinosaurs. They came onto the scene of dinosaurian evolution during its final stages and disap- peared, along with certain other final sur- vivors, during that great transition between Mesozoic and Cenozoic times, when rep- tilian dominance gradually yet unequivo- cally gave way to mammalian dominance on the earth. Their history was relatively short, but while it lasted it was varied, in- teresting, and successful.

83

10

Adaptations of the Dinosaurs

IME FLIES, but the life of the world goes | on. Today fat cattle graze across the * western prairie where yesterday there were bison. Today the white-faced steers are rounded up by cowboys, to be shipped to market, where yesterday the bison was trailed and hunted by the wolf. Life is a continuous round and an unending struggle between the hunter and the hunted, it is a story of many kinds of plants and animals fitting into their various roles by means of adaptation to the environment.

So it was in the days of the dinosaurs. Then as now there were the plant-eaters, getting their livelihood direct from the green products of Mother Earth. Then as now there were the hunters, feeding upon the inoffensive herbivores. There were the

large plant-eaters and the small plant-eaters, .

the large hunters and the small hunters. There were the upland forms and the ani- mals of the swamps, the rivers, and the lakes. There were the tree climbers and the diggers in the earth. All formed a part ot the ecology of the time—that complex rela- tionship between the various forms of life, the “balance of Nature” as we often call it, whereby each plant and each animal is adjusted to the topography, the climate, and the life that surrounds it.

The adaptations of the dinosaurs were numerous, for in Mesozoic days these rep- tiles filled many of the “ecological niches” that are occupied by the mammals of our own time.

Some of the dinosaurs were large and others were small, as we have already seen. The small dinosaurs, such as the “bird catcher,” Ornitholestes, retained many of

84

the characters as well as the pose of their thecodont ancestors, while the large dino- saurs, such as the great bipedal carnivore, Tyrannosaurus, or the quadrupedal giant, Brontosaurus, showed many specializations in form and in pose over their small ancestors.

As has been pointed out on a preceding page, growing big isn’t a simple matter of duplicating a small-scale animal on a large

scale. The large animal is confronted by

many problems of mechanics, of stresses and strains, which never bother the small animal. On the other hand, the large animal is relieved to a certain extent of some prob- lems, of heat loss for instance, that are im- portant in the physiology of the small animal.

As the giant dinosaurs increased, there were many adaptations as a result of the stresses and strains placed upon bone, muscle, and ligament consequent upon the ever-increasing bulk of these animals. Compare the giant Tyrannosaurus with the small Ornitholestes. Tyrannosaurus, al- though a two-legged dinosaur like his small cousin, lost the lightness and graceful- ness of limb and foot that were so char- acteristic of Ornitholestes. In Tyranno- saurus there were several tons of weight to be carried around, so that the legs became very heavy and strong, while the feet broadened to form a good support and to furnish traction against the ground.

In an upright animal of gigantic size, such as Tyrannosaurus, the strain on the hips—the fulcrum for the body—must have been enormous. Thus, it can be seen that the connection between the hipbones and

= = ON NN eee

the backbone in this animal was strength- ened by the lengthening of the sacrum, so that an additional vertebra became attached to the upper hipbones, the ilia. Compare this with the comparatively small attach- ment between the backbone and the hips in little Ornitholestes.

It is in the great sauropods, however, that we see the most advanced adaptations to large size. These huge dinosaurs, 70 or 80 feet in length and weighing 20 or 30 or 40 tons, must have experienced problems in mechanics that have never before or since plagued a land-living animal.

So it is that the limbs in these dinosaurs were heavy and postlike and the individual bones were extraordinarily massive and dense—veritable pillars for the support of the animal. Likewise, the feet of these giant sauropods were short and broad, so that they formed massive, round pediments through which the weight of the body was thrust against the earth.

Like the lacy trusses of a cantilever

STRENGTH AND LIGHTNESS simul- taneously achieved: a bone from the neck of the giant sauropod dinosaur, Brontosaurus. Note the concentration of bony material along lines of stress and the formation of hol- lows in other portions

From Osborn and Mook, 1921

bridge, the backbone of Brontosaurus stretched between the strong abutments of the limbs and their girdles, and beyond, to form the neck and the tail. Here was a problem that required for its solution strength combined with lightness; strength upon which to hang the many tons of body, neck, and tail, lightness so that the vertebral column itself, necessarily large because of the needed strength, would not be over- burdened by a great amount ot “dead weight” of bone. The problem was solved by the inexorable processes of evolution, so that the vertebrae became “excavated” where bone wasn’t needed. In other words, bone was formed along the lines where stresses would come and it was taken away from those areas where there were no par- ticular stresses, just as in the trusses of the steel bridge or in the flying buttresses of a Gothic church, strength is achieved without a resort to massiveness. In addition, the spinal column in the sauropods was strengthened by extra articulations between the vertebrae, which gave in effect addi- tional interlocking joints to strengthen the backbone without decreasing its flexibility.

The dinosaurs lived in all kinds of sur- roundings. Some of them were upland forms, well adapted to fairly rapid progres- sion over hard ground. Such was the case with many of the bipedal theropods, the small carnivores such as Ornitholestes and the large carnivores such as Allosaurus and Tyrannosaurus. Such was also the case with many of the quadrupedal types, par- ticularly the horned dinosaurs of Cre- taceous times and many of the armored dinosaurs.

These upland forms were seemingly rather active—at least for reptiles. The bipedal animals were able to run or walk about with some show of speed, by virtue

85

oe ee ee, ey

Brachiosaurus

of their swinging, two-legged stride. The quadrupedal forms, such as the horned dinosaurs, were built as efficient walkers; the limbs were strong and the belly was raised high off the ground.

Other dinosaurs were lowland animals, living in marshy country or along the shores of rivers and lakes. It would seem that these animals spent much of their time in the water, feeding among the lush marsh plants or even venturing out into deeper waters to escape from their traditional enemies, the giant carnivores.

Many of the lowland dinosaurs were probably slow and sluggish. It is likely that Brontosaurus and his relatives spent much of their time moving along slowly, feeding upon green plants. Perhaps these giant sauropods passed considerable time in mo- tionless torpor, as do some of the large crocodiles in our own times.

The aquatic habits of the sauropods are attested to by the structure of the skull in some of them. In Diplodocus, for instance, the nostrils were placed on the top of the head, as is so often the case in water-living beasts, to facilitate breathing. This develop- ment is accentuated in the gigantic Brachiosaurus from Africa, in which the nostrils were raised so as to protrude above the top line of the brain case.

The truly aquatic dinosaurs were, how- ever, the trachodonts or hadrosaurians. As

<& Brachiosaurus could breathe with only a small portion of the head above the surface of the water. The nostrils were on an eminence on top of the head. Para- saurolophus, a duck-billed dinosaur, had a greatly elongated nasal passage within the crest. This presum- ably formed an air storage chamber which enabled the animal to remain under water for a considerable period

Drawings by John C. Germann

mentioned on a previous page, we know that these dinosaurs had webbed feet, from the several “mummies” that have been pre- served. In addition, the trachodonts had deep, narrow tails that must have aided in swimming—tails that were curiously strengthened and perhaps stiffened by calci- fication of the tendons of the back muscles, to form a lattice-work binding the bones of the spinal column.

But the most striking features of the trachodonts were the developments of ac- cessory structures on the top of the skull in many forms, as already described and illustrated. These crests, in such animals as Corythosaurus, Lambeosaurus, and Para- saurolophus, were formed almost entirely by the bones surrounding the nostrils, the premaxillary and nasal bones, and to a small extent by the frontal bones of the forehead. It would seem from dissections that have been made, that the crests in the hadrosaurs were occupied by the nasal passages which were thereby lengthened so that they formed air storage chambers. The usefulness of such an arrangement to an aquatic animal that may have kept the head submerged for considerable periods of time is obvious. | It has even been suggested that certain dinosaurs may have been tree-climbing reptiles, living a life not unlike that of some of our larger tree-climbing mammals of the present day. One form in_ particular, Hypsilophodon (hips-i-Lor-o-don), ) shows grasping feet that would seem to have been adapted for clasping branches. This was a rather small dinosaur, and there is no reason why it might not have lived in trees.

The ancestral thecodont reptiles were carnivorous, and the carnivorous diet was retained by most of the theropods. As might be expected, the giant theropods, such as

87

Allosaurus and Tyrannosaurus, had widely gaping mouths armed with huge, bladelike teeth. Only in the toothless “ostrich dino- saurs’ such as Struthiomimus was there a departure from this primitive or ancestral] carnivorous diet among the theropods.

Most of the dinosaurs were, however, herbivorous, living upon green plants. In this category, we find the sauropods among the Saurischia and all of the dinosaurs belonging to the order Ornithischia. Con- sequently there were various adaptations for eating plant food in these animals.

In the giant sauropods dental adaptation seemed to be mainly a process of limiting the teeth to the front of the jaws and trans- forming them into rather weak pegs. How such teeth, mounted in such small jaws, could serve to tear off enough leaves from their stems to keep these huge dinosaurs going, is a problem that baflles the imagina- tion, yet the evidence is there and cannot be refuted. These dinosaurs did live, and very successfully too, for many millions of vears.

In the ornithischians the teeth were re- stricted to the sides of the jaws, the front of the jaw being transformed into a sort of a beak, as mentioned above, consisting of the premaxillary bones in the upper jaw and of a new element, the predentary bone, in the lower jaw. This sharp, birdlike beak must have served these dinosaurs for the purpose of tearing green leaves away from their stems.

When it came to the process of chopping and chewing the plant food into digestible bits, the ornithischians were admirably provided with dental batteries of consider- able complexity. In the primitive campto- saurs there was a row of fluted teeth on either side of each jaw, which when worn maintained sharp edges that would serve

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|

to chop the food by a scissor-like motion of the jaws.

Modifications of these teeth occurred in the armored dinosaurs and in the cera- topsians or horned dinosaurs, but it was in the aquatic hadrosaurs that the dental bat- tery attained its most specialized form. There was in these dinosaurs a tremendous increase in the number of the teeth so that instead of a relatively few teeth in each jaw, above and below, there were in each jaw some 500 teeth. Thus there was a total of about 2000 teeth in the mouth of a typical duck-billed dinosaur. These teeth, which were small and rather lozenge- shaped, were arranged in several closely packed rows. When worn, the overlapping surfaces of the teeth formed a rough pave- ment that served to grind the food, mill- fashion, into a pulpy mass. As in a well- organized army, there was a large number

———

of “replacements,” so that as the teeth in use were worn they were pushed out, until they wore away completely, to be replaced by new teeth. It is a complex structure and a difficult process to describe, but the ad- vantage of such an arrangement is obvious. © Adaptations to diet were not only re- flected in the structure of the teeth of the dinosaurs, but also extended to the develop- ment and the articulation of the jaws. This follows the principle that biting and chew- ing among the vertebrates are not alone functions of the teeth, but are dependent upon the structure of the skull, the strength of various muscles, and the movements of the jaws.

In the Saurischia the jaws worked on what might be called the “scissor principle.” This may be explained by saying that the articulation or fulcrum for the jaws was on a line with the edges of the jaws and

the teeth, so that the mouth was closed by a scissor-like action, whereby the sharp teeth of the lower jaw were sheared past those of the skull. In this manner, the car- nivorous theropods were able to tear and cut their unfortunate victims into sizable chunks that might be swallowed.

\It is interesting to see that the giant

‘carnivores had an expansion of the back

part of the lower jaw, which afforded in- creased attachments for the powerful muscles that activated the bite in these fierce hunters. It is interesting to see, also, that in the toothless, fruit-eating “ostrich dinosaurs,’ such as Struthiomimus, the typical theropod method of jaw articulation was retained, even though these animals had departed from the ancestral car- nivorous diet.

What about the great sauropods? Here again, the primitive “scissor” articulation of the jaws was retained, even though these huge dinosaurs had turned entirely to a vegetarian diet. The heritage of the an- cestor was retained in the descendant.

The reason for this lack of specialization in the jaws of the sauropods is probably to be found in the fact that these great dinosaurs seemed to have indulged in very little if any chewing of their food. They simply cropped the plants that came within reach of their small front teeth and then swallowed whole the green stuff, to be worked on by the gastric juices of the digestive tract.

In the more highly developed Orni- thischia there was a departure from the generalized form and articulation of the saurischian jaws. The Ornithischia, as we know, were herbivorous, and it would seem that they were able to cut and chop and in some cases even to grind their food between their lateral dental batteries. Con-

89 |

oe

sequently, in these dinosaurs the jaw articulation was depressed so that it was placed on a level much lower than that of the teeth. An analysis of the movements of the jaws in these animals will show that this articulation served to bring all of the upper and lower teeth into contact at about the same time, in what might be called a “nut-cracker” or crushing action. This method of chewing is an obvious advantage to a plant-eating animal, particularly if the animal indulges at all in the pleasure of grinding its food.

The dinosaurs developed many bodily weapons for “defense,” whether such de- fense was of the passive variety, or of the more active and vigorous method of de- fense by offense and counter-offense. For the world of the dinosaurs was one of unending strife, of a constant struggle be- tween those that would eat and those that

would rather not be eaten.

In the carnivorous theropods the teeth constituted the principal means of defense. Needless to say, “defense” in these animals was mainly of the offensive variety; they were able to survive because of their pugnacity.

Ifis quite possible that these dinosaurs also used the hind feet in fighting, and that they were able to claw and scratch with their hooklike hands.

Many of the dinosaurs sought safety in flight. This was true of the smaller theropods such as Ornitholestes and Struthiomimus, and in some of the Omnithischia, notably the duck-bills. In the case of the trachodonts, it is likely that running away was directional—in other words, that these animals would make for the water as soon as one of the great car- nivores came over the horizon. So with them there would be a dash for the shore, a great deal of splashing about in the

A reconstruction of the head of Pachy-

cephalosaurus. Note the ornate nobs A.M.N.H. photograph

A The champion bonehead, Pachycephalo- saurus, whose name means “the thick-headed reptile.” All of the space above the brain is occupied by solid, dense bone

90

shallows, with water flying up in a high spray, and finally a quiet escape through the friendly deep waters.

Many of the ornithischian dinosaurs were armored in one way or another. In the true “armored dinosaurs,” the stegosaurs and ankylosaurs, there were protecting plates and spikes, which reached the climax of their development in such animals as Ankylosaurus and Nodosaurus. These dino- saurs were the armadillos of their day. When danger threatened, it was necessary only to curl up, or possibly to flatten out against the ground and let the attack rage past. These animals were not, however, merely passive defenders of their rights. Almost all of them had spikes or clubs on the end of the tail, lethal weapons of great value in beating off an attack.

Some of the ornithischian dinosaurs, the troddonts, were remarkable in the protec- tion given to the brain by the skull. In these animals the skull roof became enormously massive, not through the development of sinus cavities as is usual in the vertebrates, but by the actual thickening of the bones. In one of these animals, for instance, there was a protection of some ten inches of solid, dense bone above the brain, although why such a lowly brain should need such vault- like protection is something to wonder about.

The horned dinosaurs, it would seem, in- dulged in “active defense.” These were the “thinoceroses” of their day, blundering across upland glades and challenging all potential enemies by the power of their

=> An earlier form of the boneheaded dinosaurs, Troddon, an animal only about six feet long but already showing promise of a bonehead to brag about

Drawing by John C. Germann

strong bodies and the length of their horns. Triceratops might face his adversary with lowered head, the long horns pointing for- ward to impale his foe, the huge frill, to which were attached the powerful neck muscles, flaring up behind as a protection for his neck and back. With a short rush his attack was one of great power. He needed it, in a world where Tyrannosaurus was running rampant.

Finally, some of the dinosaurs were pro- tected, or at least partially protected, by their great size. These were the giant sauro- pods. They were so large that only the largest of contemporary carnivores even dared to attack them. Perhaps at that the carnivores were forced to limit their dep- redations to such of the giants as might be injured, or bogged down, or possibly to the little sauropods.

It must always be kept in mind that the dinosaurs were reptiles. Being reptiles, their life was less well organized and less well directed than are the activities of the mammals so familiar to most of us. It is certain that the dinosaurs had a reptilian brain of comparatively lowly form and organization, so these were not what we would call “thinking animals.” Their daily

Sacre

Enlargement

round was largely a series of reflex actions, of responses to external stimuli. They muddled through life in a ponderous world.

Not only was the brain of the dinosaurs of lowly form, but it was extraordinarily small, when one considers what huge ani- mals these reptiles were. It is a well-known fact, established many years ago, that large animals have smaller brains in comparison to their size than do small animals. For instance, an elephant weighing six tons has a brain weighing about ten pounds, which is approximately 1/10 of one per cent of the body weight. Compare the latter figures with those for a sheep, in which the body weight is about 75 pounds and the brain weight about three and a half ounces, in a ratio of 3/10 of one per cent of brain to body weight. Or compare the body weight of about seventeen pounds to a brain weight of two and a half ounces in a fox-terrier dog, which gives a ratio of brain to body weight of almost 9/10 of one per cent. From the above figures it is readily seen that the brain of the elephant is much bigger than that of the sheep or the dog even though in relation to body weight it is smaller. Giantism in the ele-

Brachi

phant’s body has been accompanied by a certain degree of giantism in the brain, but in the dinosaurs not only was the relative size of the brain small, its actual size was also very small. Thus in Stegosaurus, an animal as heavy as a modern elephant, the brain was no larger than that of a small kitten.

Indeed the diameter of the brain in the large dinosaurs was in many cases less than that of the spinal cord, while in size it was much smaller than the brachial and sacral enlargements of the cord in the shoulders and hips which served to control the move- ments of the legs and tail. For instance, in Stegosaurus, as already mentioned, the sacral enlargement was 20 times as large as the brain. As a matter of fact, the dino- saur brain was probably, in the main, a receptor mechanism—a center where the visual images, the odors, and the sounds coming in from the outside world were received so that the animal's activity might be correlated with the environmental con- ditions indicated by these outside stimuli.

One interesting development in the dino- saurs was the great enlargement of the pituitary body attached to the base of the brain. In all but the “giants” among recent

The great size of dinosaurs may have been caused by enlargement of the pitui- tary gland. This illustration shows the relatively large size of the pituitary body in relation to the primitive brain of a troddont dinosaur

Drawing by John C. Germann

vertebrates this pituitary body is relatively small. In the dinosaurs it was relatively large, and it is an interesting fact that in the huge sauropods it was very large. There was evidently a correlation between the enlargement of the pituitary body and the size of dinosaurs.

The functions of the pituitary body in recent vertebrates are various, but among other things the anterior lobes of this gland, the very part of the pituitary body which seemingly was enlarged in the dinosaurs. secretes the growth hormone. This means that animals with large, active pituitaries, are large animals. So it is not surprising to see that in those dinosaurs which showed an excessive enlargement of the pituitary, the individual reached gigantic propor- tions.

Of course giantism in the dinosaurs was closely related to the environment. Those dinosaurs with active growth hormone se- cretions and enlarged pituitaries became dominant because the climatic and. other environmental conditions of later Mesozoic times were favorable to giantism. It is all a part of a correlated and complex picture, the whole of which must always be kept in mind.

93

i

Dinosaurian Associations

E HAVE HAD A GLIMPSE at the va-

riety of dinosaurian evolution.

We have seen how these domi- nant reptiles of the Mesozoic land became adapted to numerous environments and to different modes of life. All of this has given us a fairly comprehensive view of the dino- saurs as zoological units—as living mecha- nisms that have become modified in various fashions, while at the same time they have maintained certain basic relationships to one another as members of two great rep- tilian orders having a common ancestry. Yet the picture is not complete, because little attention has as yet been given to the “ecological relationships” of the dinosaurs, to those complex interrelationships that are present in any community of animals. Let us look at the dinosaurs as they dwelt to- gether, let us see in the mind’s eye how they lived and fought and died.

The dinosaurs, as has been said—perhaps to the point of monotony—persisted over a period of great geological length. They lived in all quarters of the globe. Obviously it is impossible to attempt in a few brief paragraphs to describe all of the dinosaurs of the Mesozoic on all of the continents. Nor is such a procedure necessary. The dinosaurs to well- established types, characteristic of each of the Mesozoic periods. A fairly adequate

conformed certain

picture of the more specialized dinosaurian assemblages may be had by picking out one dinosaurian association from the Jurassic period and another from the Cretaceous. Of all the Jurassic dinosaur faunas, none is better known nor more characteristic than the so-called Morrison fauna—the dinosaurs

pee

found in the Morrison formation of Wyo- ming, Colorado, and certain other western states. These dinosaurs are found together, and under such conditions of deposition that there can be no doubt that they all lived at the same time.

In the dim and distant days of the Jurassic the West was not a land of high mountains and broad prairies, a land of clear blue air, as it now is. Indeed, quite the reverse conditions prevailed. It was a land of low-lying tropical swamps, of steamy jungles and marshes where the sun filtered through dense, monotonously green foliage—palms and ferns and water-plants. Here lived the Morrison dinosaurs, an integrated association of animals, the small and the large, the hunted and the hunters. There was a pattern of life, just as there is today on the western plain, but it was a pattern on a giant scale.

Darting back and forth through the dense undergrowth was Ornitholestes, the little carnivore, the one dinosaur of the Jurassic that retained to a considerable de- gree the structure and the habits of its distant Triassic ancestors. Ornitholestes was certainly one of the less conspicuous members of the Jurassic fauna, a small ani- mal stalking small prey.

There was nothing shy about Allosaurus, the tyrant of the Jurassic scene. Here was a carnivore of gigantic size, stalking across the dry ground between swamps and lakes, hunting giant prey with nothing to fear but other members of his own species.

Dominating the scene in bulk, but not in spirit, were the giant vegetarians Brontosaurus and Diplodocus. Theirs was

‘a generally peaceful life, a life lived in the

swamps and marshes, where they fed on the leaves of lush plants, waded shoulder deep through small lakes, lay for hours in rep- tilian torpor, engulfed by the damp warmth of the jungle. There were occasional punc- tuations to this quiet life, intervals of wild alarums, of attacks by Allosaurus and his kin, of escape to the deep protective waters of the lakes or to the soft, impassable mire of the swamps where the giants were safe, where they might resume their slow, ponderous round of daily inactivity.

Then there was Stegosaurus, the armored dinosaur, living in the uplands, if the high ground between the swamps and marshes may be called uplands, feeding upon green plants, protecting himself from the attacks of Allosaurus by a “hedgehog defense,” by a passive presentation to the attacker of thick hide and plates, and cruel spikes on the end of a viciously swinging tail. This much can be said for Stegosaurus, at least he met aggressive attack with a certain de- gree of aggressive defense, and thus he was able to survive in a harsh world.

Finally, among the Morrison dinosaurs there was Camptosaurus, one of the two- legged ornithopods, a rather small and in- offensive plant-eating animal. Campto- saurus was perhaps too large to dart into the undergrowth as did Ornitholestes, but it is probable that this little dinosaur had to make himself relatively inconspicuous or even scarce on occasions if he were to sur- vive. At this Camptosaurus was eminently successful, for he and his descendants sur- vived into the following geologic period, which is more than can be said for some of the other Jurassic dinosaurs.

Such was life in the Jurassic.

Let us now go forward from the Jurassic to catch a glimpse of the Cretaceous dino- saurs. This time we will choose the fauna

which lived in North America in late Cretaceous times and which is found in the Belly River formation, now expesed in certain portions of southern Alberta.

At that stage in the history of the earth conditions were quite different from what they had been in Jurassic times. North America was still a country having a warm, equable climate, but it wasn’t the low-lying tropical region that it had been when Brontosaurus and Allosaurus were alive. It was now more of a semi-tropical region, with palms and ferns along the shores of the rivers, inland seas, and lakes, but with upland regions of some height forested with such familiar trees as oaks and willows, sassafras and hickory. This was the environ- ment in which the late Cretaceous dino- saurs lived.

Of these later dinosaurs Struthiomimus, the so-called ostrich dinosaur, played one of the lesser roles in the drama of life. Here was a relatively small and inoffensive ani- mal, occupying much the same position in the Cretaceous scene that Camptosaurus had in the Jurassic landscape. Struthiomi- mus lived on succulent plants and perhaps upon such small animal fry as he might be able to catch. He was long of hind limb and slender of build—obviously designed to vanish with great speed the moment any of the ever-dangerous carnivores might appear over the horizon.

Of the carnivores, Gorgosaurus was typical. This was a larger and more active cousin of the Jurassic Allosaurus, and an animal that was specialized to prey upon the various large herbivorous dinosaurs that inhabited the Cretaceous landscape. It was an advanced member of the line of car- nivorous dinosaurs, a line which culminated with the gigantic Tyrannosaurus, of upper- most Cretaceous age.

Of the large herbivorous dinosaurs,

95

there was a great variety of forms. Along the rivers and lake shores were the semi- aquatic duck-bills, Trachodon and_ his crested cousins, Corythosaurus and Para- saurolophus. These animals fed upon the water-plants of the bank or of the strand, and perhaps upon certain mollusks, too. They were water-lovers and even when on land were ready to dash into the protection of their aquatic environment at an instant’s notice. Needless to say, such notice was usually the sudden appearance of Gorgo- sourus or one of his predatory relatives.

Inhabiting the uplands were the armored and the horned dinosaurs, plant-eaters that were well equipped to beat off or with- stand the attacks of the fierce carnivores. Palaeoscincus was a typical armored form, a veritable dinosaurian tank, or armadillo, completely encased by heavy armor plate, with a spiked tail capable of wreaking havoc on anything that came within reach of its powerful sweep.

Of the horned dinosaurs, Monoclonius

96

and Styracosaurus were the Belly River representatives. These powerful animals, with their efficient nose horns, were seem- ingly quite capable of repulsing the attacks of the carnivores under ordinary conditions.

Such was the pattern of life in Cretaceous times, one that repeated the pattern of the Jurassic scene but with the use of different elements, a pattern that is repeated even today on a less grandiose but perhaps on a more efficient scale among our mammals. If we can visualize this pattern, a mélange of interrelated animals running through geologic time, we will be that much better able to appreciate the structural modifica- tions which in the dinosaurs attained such a variety of forms. Let us therefore remem- ber the pattern as it has been pictured here, a pattern of hunter and hunted, of carnivore and herbivore, of large and small, of upland and aquatic, all living together and adjust- ing themselves to each other. That is the key to the adaptive radiation of the dinosaurs.

12

Flight

'N Jurassic TIMEs there occurred a new and a very important event in the long and complex history of the verte- brates. This was the development of the

“power of flight.

——The story of the backboned animals throughout their pre-Jurassic history was one of animals living in the waters, or venturing out of this ancestral habitat to try their fortunes on the solid land. During a stretch of geologic time of great im- mensity, a period measured by the hun- dreds of millions of years, the vertebrates were restricted to the waters and to the lands, where, as we have already seen, they developed an astonishing variety of forms, adapted to numerous environments and methods of life. But it was not until the advent of Jurassic days, when tropical forests steamed beneath the sun and hordes of dinosaurs ruled the land, that the verte- brates first ventured into the thin air, to soar upon outstretched wings, free from the trammels of an earth-bound or of an aquatic existence.

Strangely enough, two groups of animals took to the air in Jurassic times, and strangely enough, both of these groups were closely related to the dinosaurs. One group was that of the flying reptiles, the pterosaurs, which arose in the Jurassic,

~ reached the culmination of their evolution-

‘ary development in Cretaceous times, and then became extinct along with their dino- saurian cousins, during the profound transi- tion between Cretaceous and Cenozoic times. The other group was that of the birds, which likewise arose during the Jurassic, but which successfully weathered

the Cretaceous-Cenozoic transition, to in- habit the air of our present-day world.

It would seem almost as if the “time was ripe” in Jurassic days for the appearance of flying vertebrates. Perhaps a more accurate explanation would be to say that in the Jurassic period of Earth History the verte- brates had attained a complexity and per- fection of bodily makeup that made it possible for them to overcome, through evolutionary processes, the severe difficul- ties of flying.

We know from our own acquaintance with the history of the airplane that flight is no simple matter. It was attained by man only after the invention of the internal com-

bustion engine, when there was a combina-

~ tion of power and lightness sufficient to lift

the man-made wings off the ground. This

evolution of the modern airplane offers an

analogy with the evolution of the flying

vertebrates. Any backboned animal that

attempts flight must:

a.

Transform the normal type of front limbs

into wings.

b.

Become light in the body while retaining a

very strong skeleton and powerful muscles.

C.

Have a highly developed nervous system,

with a particularly fine sense of balance. Let us see how the two groups of animals

which first attempted to fly in Jurassic times

solved these problems.

Pterosauria The pterosaurs (TER-0-sawrs) were

diapsid reptiles of basic thecodont ancestry

97.

;

| They were lightly built, with hollow bones

which were strong yet at the same time remarkably light. In the skull there was an unusual amount of fusion of the bones, while the back was very short and strong, an adaptation brought about by a reduction of the number of bones making up the spinal column. The pectoral and_ pelvic girdles to which the limbs are attached

were strongly anchored to the backbone. Indeed, there was a new and special at- tachment, not found in any other animal, that held the shoulder girdle firmly to the backbone, thereby affording a _ secure anchorage for the long wings. Moreover, the breastbone or sternum, attached to the lower ends of the pectoral girdle and the ribs, was greatly enlarged to provide a

a

FLYING REPTILES. In the Jurassic form, Rhamphorhynchus, there were teeth in the jaws, and a long tail. In the advanced Cretaceous form, Pteranodon, the teeth had been lost and the

tail reduced

Restorations by John C. Germann

strong attachment for the strong breast muscles that moved the wings. In these highly modified reptiles the fourth finger ot the hand was greatly elongated, and this formed the support for a long, membranous wing. The remaining fingers were small, hooklike claws, which evidently were used for hanging onto rocks or limbs. The hind limbs were very weak, so it would seem that these flying reptiles were very poor walkers —in fact, it is doubtful whether they moved around on the level ground to any extent at all.

The flying reptiles of the Jurassic period (155 to 120 million years ago) were for the most part rather small, often no larger than sparrows or robins. They were charac- terized by the presence of teeth in the skull and lower jaw, and usually although not always by a long, rudder-like tail. The

Cretaceous pterosaurs (120 to 60 million”

years ago) were the giants among nature’s “flying machines.” Pteranodon (ter-AN-o- don), for instance, had a maximum wing- spread of some 27 feet! These large ptero- saurs were specialized beyond their Juras- sic forebears in that they had lost the teeth and the tail had become very short.

What were the habits of the pterosaurs? These were quite obviously aerial reptiles, but it is doubtful whether they flew as much as they glided, or soared. These ani- mals were lightly built—even the giant form, Pteranodon, with a wing-spread of more than 20 feet, had a relatively small body—and it would seem probable that they were living gliders, majestically soaring back and forth on the warm currents of air rising from the tropical landscape beneath them. Certainly they had a less powerful and efficient muscular system for moving the wings than do our modern flying birds.

Whatever may have been the flying

habits of the pterosaurs, it is certain that these animals had a less efficient wing than do either the birds or the bats. In the ptero- saurs there was a single series of bones, the fourth finger, running along the front edge of the wing as a support. Consequently, if the wing membrane should be torn, these animals must have found flying difficult. Compare this with the several fingers that support the membrane in the bat’s wing, or with the feathers than constitute the wing of the bird. The advantages of wing construction in these modern flying verte- brates are obvious.

The brain in the pterosaurs was very large, considering that it was a reptilian brain, and it showed a strongly developed sense of sight and a weakly developed sense of smell. In these respects the pterosaurs were similar to our present-day birds; they soared aloft in search of their food, scan- ning the landscape and guiding their flight through large and efficient eyes.

Finally, it is barely possible that the pterosaurs were warm-blooded, at least par- tially so. This is a “scientific guess” but it is based upon the fact that these were spe- cialized flying vertebrates and as such must have had to sustain action over considerable periods of time. Such a feat is difficult, if not impossible, for the cold-blooded rep- tiles as we know them, but it would have been feasible should these ancient reptiles have independently attained a warm- blooded condition, similar to that of the birds or the mammals.

Such was this first pattern for vertebrate flight—a pattern that was established in Jurassic times and persisted to the end of the Cretaceous. Even though it failed to survive, just as so many other reptilian de- velopmental patterns failed to survive the Cretaceous-Cenozoic transition, it was

99

WING OF PTEROSAUR, BIRD, AND BAT

In the flying reptile, the wing AN was a membrane supported by \\\

the elongated fourth finger. The \

other Angers Wereihocke by which ww the animal could hang from rocks or limbs

In the birds, the fingers are

\ coalesced. The wing surface is formed of the stiff primary feathers, which are attached to the skin covering the lower part of the arm

> * e fret” ve bye ty

In the bat, the wing surface is a membrane, but it is supported by several elongated fingers

Drawings by John C. Germann

nonetheless successful, for it continued

-over a period of some 50 to 60 millions of

years. But it wasn’t so successful a pattern for flight as was that of the birds, or of the bats.

The Birds

Birds are little more than “glorified rep- tiles.” True enough, to the average spectator there seems to be nothing in common be- tween the gorgeous blue and white flash of the jay, screaming his indignation through the high branches of the oak tree, and the silent and sinuous menace of the blacksnake gliding through the grass, the object of the bird’s imprecations. But under- neath the feathers of the bird and the shin- ing scales gf the reptile the resemblances are there, and when the ancestries of these two apparently so dissimilar vertebrates are traced back through the fossil record the resemblances become all the more signifi- cant—the bird becomes ever more reptilian, so that there can be little doubt as to its earliest orgin.

The birds, although classified as a separate class of the vertebrates, are essen- tially of basic thecodont ancestry. They are lightly built, with strong, hollow bones. Not only are the bones extraordinarily pneumatic, for the sake of lightness, but also there are a number of air sacs in the body of the bird, which further contributes to its flying ability. The skull shows an un- usual amount of fusion of the bones (just as was the case in the pterosaurs). The back is short and strong, while the neck is rather long. The pectoral and pelvic girdles are very strong; the latter is firmly attached to the spinal column by a greatly lengthened and strengthened series of articulations be- tween the vertebrae and the sacral portion of the pelvis. In the typical flying birds the

breastbone has become greatly enlarged to afford anchorage for the powerful pectoral muscles that activate the wings. In the large ground-living birds such as the ostrich, no such development of the breastbone is seen, but there is reason to think that in these cases there has been a secondary reduction of this element from a formerly large struc- ture. Thus far in this summary of the char- acteristics of the birds we see a considerable amount of parallelism with the flying rep- tiles.