Page images
PDF
EPUB

Pampas; by Auchenia, or llama, of which three extinct species inhabited Bolivia, in which country two allied but extinct genera, Palaeolama and Camelotherium, have also been found. Three species of deer (Cervus), from the Pampas deposits, complete the list of Pliocene Ungulates. Proboscidea.—The cave species of Mastodon is found also in the Pampas deposits, and another in the Andes of Chili and Bolivia. Rodents—These are not so numerous as in the caves. There are species of the existing genera, Kerodon and Cavia (Caviidae); Lagostomus (Chinchillidae); Ctenomys (Octodontidae); Lepus (hare); Hesperomys and Oxymycterus (Muridae); Arvicola, a genus not living in South America; and an extinct genus, Cardiodus. There is also a remarkable extinct form, Typotherium, larger than the capybara, and having affinities to Edentates and Ungulates. Three species have been found in the Pampas deposits. Edentata.-These are as abundant and remarkable as in the cave deposits. Scelidotherium, Megatherium, Megalonyx, Glossotherium and Dasypus, have already been noticed as from the Brazilian caves. We have here, in addition, the huge Mylodon allied to the Megatherium, and the allied genera—Gnathopsis and Lestodon. We then come to the huge extinct armadillos, Glyptodon and Schistopleurum, the former consisting of numerous species, some of which were as large as an elephant. Another genus, Eutatus, is allied to the living three-banded armadillos; and a species of the existing genus Euphractus has been found in Bolivia. Toxodontidae.—There remain a number of huge animals rivalling the Megatherium in size, and forming the genera Toxodon and Nesodon, but whose position is doubtful. . Several species have been found in the deposits of the Pampas and Patagonia. They are allied at once to Ungulates, Rodents, Edentates, and the aquatic Sirenia, in so puzzling a manner that it is impossible to determine to what order they belong, or whether they require a new order to be formed for their reception. Some are believed to date back to the Miocene period, and they indicate what strange forms may still be discovered, should any productive deposits be found in South America of middle Tertiary age.

Pliocene Mammalia of the Antilles—These may be noticed here, as they are of special interest, proving the connection of the larger West Indian Islands with the Continent some time in the later Tertiary period. They consist of remains of two large animals belonging to the South American Chinchillidae, found in cave deposits in the island of Anguilla, and forming two new genera, Amblyrhiza and Locomylus; and remain allied to Megalonya: from Cuba, which have been named Megalocnus and Myomorphus.

Eocene fauna of South America.-The few remains yet discovered in the Tertiary deposits of the Pampas which are believed to be of Eocene age, are exceedingly interesting, because they show us another change in the scenery of the great drama of life; there being apparently a considerable resemblance, at this epoch, between South America and Europe. They consist of a large extinct feline animal, Eutemnodus; of Palaeotherium and Anoplotherium, the well-known extinct Ungulates of the European Tertiaries, and which have never been found in North America; and of three genera, of Rodents, Theridromys, allied to Echimys, and found also in the Eocene and Miocene of France; Megamys, allied to the living Capromys of the Antilles, and also to Palaeomys, an extinct form of the French Miocene; and a very large animal referred to Arvicola, a genus found also in the Pliocene deposits of South America, and abundant in the northern hemisphere. No Edentates have been found.

The resemblances of this fauna to that of Europe rather than to any part of America, are so strong, that they can hardly be accidental. We greatly want, however, more information on this point, as well as some corresponding evidences as to the condition of West and South Africa about the same epoch, before we can venture to speculate on their bearing as regards the early migrations of organic forms.

General Remarks on the Extinct Mammalian Fauna of the Old and New Worlds—Leaving the more special applications of palaeontological evidence to be made after discussing the relations of the existing fauna of the several regions, we propose here to indicate briefly, some of the more general deductions from the evidence which has now been laid before our readers. The first, and perhaps the most startling fact brought out by our systematic review, is the very recent and almost universal change that has taken place in the character of the fauna, over all the areas we have been considering; a change which seems to be altogether unprecedented in the past history of the same countries as revealed by the geological record. In Europe, in North America, and in South America, we have evidence that a very similar change occurred about the same time. In all three we find, in the most recent deposits—cave-earths, peat-bogs, and gravels—the remains of a whole series of large animals, which have since become wholly extinct or only survive in far-distant lands. In Europe, the great Irish elk, the Machairodus and cave-lion, the rhinoceros, hippopotamus, and elephant;-in North America, equally large felines, horses and tapirs larger than any now living, a llama as large as a camel, great mastodons and elephants, and abundance of huge megatheroid animals of almost equal size;—in South America these same megatheroids in greater variety, numerous huge armadillos, a mastodon, large horses and tapirs, large porcupines, two forms of antelope, numerous bears and felines,including a Machairodus, and a large monkey, have all become extinct since the deposition of the most recent of the fossilbearing strata. This is certainly not a great while ago, geologically; and it is almost certain that this great organic revolution, implying physical changes of such vast proportions that they must have been due to causes of adequate intensity and proportionate range, has taken place since man lived on the earth. This is proved to have been the case in Europe, and is supported by much evidence both as regards North and South America. It is clear that so complete and sudden a change in the higher forms of life, does not represent the normal state of things. Species and genera have not, at all times, become so rapidly extinct. The time occupied by the “Recent period,” that is the time since these changes took place is, geologically, minute. The time of the whole of the Post-Pliocene period, as measured by the amount of physical and general organic change known to have taken place, is exceedingly small when compared with the duration of the Pliocene period, and still smaller, probably, as compared with the Miocene. Yet during these two periods we meet with no such break in the continuity of the forms of life, no such radical change in the character of the fauna (though the number of specific and generic changes may be as great) as we find in passing from the Post-Pliocene to recent times. For example, in Central Europe numerous hyaenas, rhinoceroses, and antelopes, with the great Machairodus, continued from Miocene all through Pliocene into Post-Pliocene times; while hippopotami and elephants continued to live through a good part of the Pliocene and Post-Pliocene periods,-and then all suddenly became extinct or left the country. In North America there has been more movement of the fauna in all the periods; but we have similar great felines, horses, mastodons, and elephants, in the Pliocene and Post-Pliocene periods, while Rhinoceros is common to the Miocene and Pliocene, and camels range continuously from Miocene, through Pliocene, to Post-Pliocene times;-when all alike became extinct. Even in South America the evidence is, as far as it goes, all the same way. We find Machairodus, Equus, Mastodon, Megatherium, Scelidotherium, Megalonya, and numerous gigantic armadillos, alike in the caves and in the stratified tertiary deposits of the Pampas;–yet all have since passed away.

It is clear, therefore, that we are now in an altogether exceptional period of the earth's history. We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared ; and it is, no doubt, a much better world for us now they have gone. Yet it is surely a marvellous fact, and one that has hardly been sufficiently dwelt upon, this sudden dying out of so many large mammalia, not in one place only but over half the land surface of the globe. We cannot but believe that there must have been some physical cause for this great change; and it must have been a cause capable of acting almost simultaneously over large portions of the earth's surface, and one which, as far as the Tertiary period at least is concerned, was of an exceptional character. Such a cause exists in the great and recent physical change known as “the Glacial epoch.” We have proof in both Europe and North America, that just about the time these large animals were disappearing, all the northern parts of these continents were wrapped in a mantle of ice; and we have every reason to believe that the presence of this large quantity of ice (known to have been thousands of feet if not some miles in thickness) must have acted in various ways to have produced alterations of level of the ocean as well as vast local floods, which would have combined with the excessive cold to destroy animal life. There is great difference of opinion among geologists and physicists as to the extent, nature, and duration of the Glacial epoch. Some believe it to have prevailed alternately in the northern and southern hemispheres; others that it was simultaneous in both. Some think there was a succession of cold periods, each lasting many thousands of years, but with intercalated warm periods of equal duration; others deny that there is any evidence of such changes, and maintain that the Glacial epoch was one continuous period of arctic conditions in the temperate zones, with some fluctuations perhaps but with no regular alternations of warm periods. Some believe in a huge ice-cap covering the whole northern hemisphere from the pole to near 50° north latitude in the eastern, and 40° in the western hemisphere; while others impute the observed effects either to glaciers from local centres, or to floating icebergs of vast size passing over the surface during a period of submersion. Without venturing to decide which of these various theories will be ultimately proved to be correct, we may state, that there is an increasing belief among geologists in the long duration of this ice-period, and the vast extent and great thickness attained by the ice-sheet. One of the most recent, and not the least able, of the writers on this question (Mr. Belt) shows strong reasons for adopting the view that the ice-period was simultaneous in both hemispheres; and he calculates that the vast amount of water abstracted from the ocean and locked up

« EelmineJätka »