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Romance of Modern Geology

<h2 class="nobreak" id="CHAPTER_XXII">CHAPTER XXII</h2> <h3>THE AGE OF MAMMALS</h3></div> The Geological Record is not perfect. There are breaks in it such as have not and may never be filled up; and it is because of these breaks that some of the divisions are made in geologic time. At present the earth's crust has only been scratched for fossils. Great parts of Asia and of Africa and of South America remain to be explored, and they may in some future generation fill the gaps of our knowledge and render superfluous some of the divisions which geologists now place in the eras of the rocks and of the fossils. But so far as we know at present there were real breaks in the history of the continents, perhaps not swift or sudden, but wholly changing the appearance and the life, vegetable and animal, of half a world, perhaps the whole world at a time. Many geologists believe that the secret of these changes lies in the core of the earth; and that, to use our old simile of the golf ball, when the tension and pressures inside the earth grow too much for its strength something gives way, and the whole world begins to change, the continents sinking under the oceans -257- and new lands arising. We shall not again consider this idea in all its bearings, or ask whether there is any simpler explanation to be found in the never-ceasing explosive tremors of the crust; but we shall only say that the last of these great changes set in at the end of the Chalk age. After that era we arrive at the period among the rocks which, with all its subdivisions, Eocene, Miocene, Pliocene, Quaternary, is classed as Cainozoic or Modern. Let us sum up the changes broadly. The Tertiary period, which now begins, has been called the Age of Lakes: but this merely means that there were great lake deposits, and it is true to say that as contrasted with a period of great waters, the Tertiary is to be considered as the period of land. That does not mean that there were in all the hundreds of thousands of years which it embraces no advances and retreats of the sea, no submergings and uprisings of the land. There certainly were. But the land was dominant, and it is the land animals and the land vegetation that are the most important and progress most. After the earth movements which occurred at the end of the Mesozoic or Secondary period there appears to have followed a period of quiet. There was a considerable area of land standing high above the waters; and there began one of the minor but considerable encroachments of the sea in North America. It is probable that the Pacific and the Atlantic joined between North and South America. At the end of this first period the sea withdrew again, and what is called the Miocene period began with a lowering of the temperature of the waters -258- of the Atlantic; and lastly followed the great extension of the land towards the north, the great withdrawal of the sea of Pliocene times, and the growing cold which led to the glacial era of the Pleistocene period. In Europe and in Asia we may note that the great areas which are now covered by the Alps and the Himalayas were at the beginning of the Tertiary period still under water and only a few signs (in the form of islands) of these mighty ranges were beginning to appear. Pre-eminently the age which comprises all these periods is the Age of Mammals. But one of the changes which European geologists first noticed was the surprising change which took place in the marine fossils. The animals of the sea which were familiar during the Chalk period nearly all disappeared and were replaced by new ones. The great saurian reptiles, from the monsters of the land to the mososaurus serpents of the sea, disappeared, and most other reptiles showed profound changes, showing a revolution in the animals of the land corresponding to that of the sea. Lastly, in this first period, the Eocene, mammals suddenly appear in force and occupy the first place among the animals. The vegetation did not change so much as might have been expected. Whence came the mammals? That, again, is one of the questions which time alone can completely answer. But the opinion of most geologists is that they arose and developed in Asia first of all, and then spread to other continents. The rise of the mammals, which, -259- unlike the reptiles, bring forth their young relatively mature and nourish and protect them, was contributing to the downfall of the reptiles, though it cannot be considered an actual cause. The mammals' young had a better chance of living and surviving than had the eggs of reptiles. Moreover, the mammals began with superior agility and higher brain-power. It is not surprising, therefore, that the invasion of the mammals resulted in the clumsy, affectionless, small-brained reptiles being driven either into extinction, or into the sedges and rushes, the swamps and lagoons, the coverts of the jungles, the crevices of the rocks, and the various by-ways which the mammals cared least to frequent, and that they have been kept there to this day. At first the mammals were not very different in habit or type from one another. Small animals, which, like the shrews, moles, and hedgehogs lived on insects were among the earliest. There were others whose toes were turning to hoofs in order to fit them for fleetness; and there were some curious creatures called Coryphodons, which were like the modern tapir, though they were tusked like boars. The Coryphodon was a slow beast, with toes like those of an elephant, though it was much smaller. In America appeared a small animal not much bigger than a fox-terrier, which was the ancestor of the horse, and of which we shall have more to say. The birds increased, and forms like those of the heron mingled in the swamps with other goose-like birds that kept in their serrated bills some traces of the teeth of their early -260- ancestors. Others, like kingfishers, flitted over the streams; and the emu, ostrich, and moa, as well as the albatross, find their earliest representatives in the Eocene times. It is impossible for us to follow, or even to enumerate, all the varied ancestral lines which sprang up, some of them already vigorous, in the early Tertiary times, and which developed so mightily in the successive ages. We can only trace the careers of a few such as are better and more popularly known, while admitting that there are many others equally interesting from a scientific or from any other point of view. From a geologist's point of view the most important, perhaps, of all the mammal developments was that of the elephant. The first mammal which geologists discovered that was like the elephant was the Mastodon, the American variety of which is called Tetrabelodon. But this Mastodon had no proper trunk as has the elephant. Instead of that he had a very long upper lip which apparently rested on his projecting upper tusks. Mr. Kipling once suggested that the elephant's trunk was originally formed by an accident—an unfortunate young elephant before the days of trunks having stopped to drink at a pool, and his nose being seized by a crocodile, who pulled and pulled till the nose lengthened out a trunk. There certainly was some reason for the elephant's trunk, which has developed, we do not quite know how, from a long nose. But a great deal has been found out about the early development of the elephant by Dr. Andrews of the British Museum. <div class="figcenter"> <ANTIMG class="w100" src="images/fpage260.png" width-obs="504" height-obs="390" alt="" /> <div class="figcaption">Evolution of the Head, Proboscis, Nostrils, and Tusks of the Elephant The drawings are to the same scale; the nostrils indicated by the letter N, the upper lips by L, and the tusks by T. </div> </div> <div class="blockquot"> 1. Mœritherium of Eocene Libya, with a flexible upper lip and the small incisor tusks. 2. Palæomastodon of Eocene Libya, with a short proboscis and powerful upper and lower tusks. 3. Mammoth (Elephas Columbi) from the State of Indiana, with gigantic upper tusks or ivories, and long proboscis with nostrils at the tip. </div> -261- Dr. Andrews was travelling in Egypt some years ago, and joined a party of officers of the great survey of Egypt in a visit to the Great Western Desert, the rainless, sandy waste west of the Nile, not very far from what is now called the Fayoum, and where in Roman days was the great Lake Mœris, now dried up to a mere brine pool, in the salt water of which the fresh-water fishes of the Nile still live. The surveying party intended to determine the geological age of these sands, which stretch for hundreds of miles, often rising into cliffs which are cut sharp by the wind and show horizontal stratification. The geologists determined that the sands of this region were of Eocene and Miocene Age, and from them Dr. Andrews brought home some very interesting bones. These included the remains of a more primitive Mastodon than any as yet known, and of an animal which he called Meritherium, which is a connecting link between elephants and other mammals. The collection included also remains of great flesh-eating beasts, and of sea cows, of tortoises, and of a snake sixty feet long! However, in regard to the history of elephants, the upshot of Dr. Andrews' most important discoveries is that we find living here in the Upper Eocene period (which is older than the age in which the Tetrabelodon Mastodon was found) an elephant ancestor of the kind to which Dr. Andrews gave the name of Palæomastodon or "ancient mastodon." We thus arrive at an ancestral elephant-like creature which serves to join the elephant stock on to more ordinary mammals. This beast was not -262- so very big, perhaps about the same size as an ordinary cart-horse. Dr. Andrews' further triumph was the additional discovery of the rather smaller animal which he called the Meritherium, and which was undoubtedly an elephant of sorts, though at first sight it has no resemblance to one, and probably had no trunk at all. It certainly had no big tusks; but its teeth make us certain that it belonged to the elephant family. "Here, then," says Sir E. Ray Lankester, "we have arrived at a form which undoubtedly was closely related to the ancestors of all the elephants, if not actually itself that ancestor, and in it we see the origin of the elephants peculiar structure. From this comparatively normal pig-like Meritherium, the wonderful elephant, with his upright face, his dependent trunk, and his huge spreading tusks has been gradually, step by step, produced. And we have seen some, at least, of the intermediate steps—the lengthening of the jaws and the increase in the size of the teeth in the Palæomastodon—carried still further on by the Tetrabelodon, and then followed by a shrinkage of the lower jaw and final evolution of the middle part of the face and upper jaw into the drooping, wonderful, prehensile trunk." The long-chinned elephant requires, however, a few moments' consideration from an altogether different point of view. This species appears to have had the widest geographical distribution of any member of the family, of which it may be regarded as the great colonising or emigrant representative. First developed in North -263- Africa, where its remains occur in the early Miocene strata of Mogara and Tunisia, this species ranged right across Europe to the confines of North-Western India, having probably reached Italy from Africa by means of a land-bridge by way of Sicily, and thence travelling through Greece into Asia. On the latter continent it appears to have given rise to the modern elephants, as remains of the former are unknown in any other part of the world. If this be true, it follows that elephants of the modern type subsequently migrated into Europe and thence to Africa, while in the other direction they wandered by way of Behring Strait to America. Hence we are led to the remarkable conclusion that while the first elephants appeared in Africa, the modern African elephant is of Asiatic parentage, and a comparatively recent immigrant into the land of its forefathers. Next to man and the carnivora, elephants appear to have been the greatest travellers the world has ever produced, for, starting from their North African birthplace, they reached by the Behring Strait route nearly to the extremity of South America, while to the north they penetrated the Arctic circle, and to the south, on their return journey, reached the coast in the neighbourhood of Cape Town. Another great traveller was the horse. The first undoubted horse-like animal was Eohippus, a little creature about eleven inches in height at the shoulder, and in general rather more like the flesh-eaters than the horses of the present day. The back was arched, the head and -264- neck were short, and the limbs of moderate length, showing no remarkable adaptation for speed. This genus had a remarkable range, having apparently originated in England (then a part of Western Europe), and migrated by way of Europe and Asia, and what is now Behring Strait, to America, where it got as far east as New Mexico. This migration of Eohippus shifted the scene of evolution to the western hemisphere, for while examples of it are continually and continuously found there in succeeding strata it only appears occasionally in Europe, as if the remains there had been those of mere emigrants. Later on the horse developed in America, growing larger till it was first as big as a collie-dog, with signs of being more adapted for speed. It then had four toes on its foot. It continued, though very gradually, to grow larger, and even more gradually its unnecessary toes grew fewer and fewer till at last they disappeared. At length appeared the horse which had only one toe. This type, that of the modern horse, first becomes known in the Upper Pliocene beds of Europe, and represents the culmination of the race. The completeness of the record of the evolution of the horse tells us something of the enormous numbers of ancestral forms which must have existed in the more than two million years that have elapsed since the first diminutive horse appeared in North America. While not strongly given to migration, in the course of time these animals wandered over the entire world, with the exception of such inaccessible -265- places as Australia and the Oceanic Islands.... It would seem that the original stock was of Eurasian derivation, though the great theatre of the evolutionary drama was soon transferred to North America, the Eurasian, African, and South American horses which appear from time to time being in all probability of North American origin. The ultimate fate of the horses in both North and South America was extinction, all wild horses of our own time, including the asses and zebras, being confined to Asia and Africa. The apparently wild bands of the American western plains, and those which roam over the pampas of South America, are the descendants of domestic horses that have escaped from human bondage, largely from the early Spanish explorers. The rhinoceroses of to-day, the one-horned Indian variety and the two-horned African rhinoceros, were preceded by a whole regiment of rhinoceroses in the Tertiary period. One such was dug out in Fleet Street during the excavation for the Daily Chronicle office. This rhinoceros had a hairy coat like the Mammoth which lived much later, and in Siberia is found sometimes side by side with the later quadruped. Many of the extinct rhinoceroses had two horns like the African square-mouthed rhinoceros, which is sometimes misleadingly called the white rhinoceros. One great extinct beast, the Elasmotherium, allied to them, had a great horn carried on a huge boss in the middle of its head instead of on the nose, while another still huger animal called the Titanotherium and found in North America had a pair of horns perched on either -266- side of its nose. As large as the rhinoceros but having a very different arrangement of the bones of its ankles and wrists and very different teeth and horns are the extraordinary creatures known as Dinoceras, whole skeletons of which have been disinterred from the Eocene strata of Wyoming in the United States by Professor Marsh. These creatures had three pairs of horns on the top of the head and a pair of great tusks as well. Nearly all these animals, though they were more brainy than the reptiles, had much smaller brains in proportion to their size than the bulk of the animals which now roam the earth, from which we may surmise that though a small brain suffices to guide a great animal machine in established ways, yet in order to learn new things in its lifetime an animal must have a big brain. The last great mammal we must mention in this series is the Arsinoitherium, which was found only a few years ago by Dr. Andrews in Egypt, in the same strata whence he obtained the fossil ancestors of the elephant. It was so called because it was found near the palace of Arsinoë, the name of the Egyptian queen of Greek race. But Arsinoitherium was far from being a graceful ladylike creature, and, resembling in general appearance a rhinoceros, had two enormous bones, which grew out of its nose on either side of it. The bones were hollow and were probably covered with skin in life; and Arsinoitherium had a wonderful and wonderfully even set of teeth. To conclude, we must add a representative mammal of this period, the Sivatherium, found in India, and the Samotherium, found in the Isle of Samos, which were like giraffes, and the beginning of the sloth-like animals, whose appearance we must, however, deal with in another chapter. <div class="figcenter"> <ANTIMG class="w100" src="images/fpage266.png" width-obs="423" height-obs="571" alt="" /> <div class="figcaption">Two Arsinoitheriums (Prehistoric Rhinoceros) at Bay before a Pack of Hyænodons The Arsinoitherium stood 5 feet 9 inches at the withers, and measured 9 feet 9 inches from snout to rump. The hyænodons (hyæna toothed) were no relation of the modern hyæna. They had bodies like the Tasmanian wolf, and were wonderfully adapted to capture both land and water living prey. (Drawn under the direction of Prof. Osborn.) </div> </div> -267- The whales whose remains are found in the Pliocene rocks differ little from those now living; but the observations geologists have been able to make upon these gigantic remains of the ancient world are too few to allow of any very precise conclusion. It is certain, however, that the fossil differs from the existing whale in certain characteristics perceptible in the bones of the skull. The discovery of an enormous fragment of a fossil whale, made at Paris in 1779, in the cellar of a wine merchant in the Rue Dauphine, created a great sensation. Science pronounced, without much hesitation, on the true origin of these remains; but the public had some difficulty in comprehending the existence of a whale in the Rue Dauphine. It was in digging some holes in his cellars that the wine merchant made this interesting discovery. His workmen found, under the pick, an enormous piece of bone buried in a yellow clay. Its complete extraction caused him a great deal of labour, and presented many difficulties. Little interested in making further discoveries, our wine merchant contented himself with raising, with the help of a chisel, a portion of the monstrous bone. The piece thus detached weighed 227 lbs. It was exhibited in the wine-shop, where large numbers of the curious went to see it. Lamanon, a naturalist of that day, who examined it, conjectured that the bone belonged to the head of a whale. As to the bone itself, it was purchased for the Teyler Museum, at Haarlem. -268- Lastly, we must not omit to mention that in the Old World the first true apes, Oreopithecus and Dryopithecus, appeared. The first of these united some of the characteristics of apes and monkeys; the second, about the same size, was more closely related to the chimpanzee and gorilla. <hr class="chap x-ebookmaker-drop" /> -269- <div style="break-after:column;"></div>

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