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ever, a few groups which seem to be late developments or recent importations into the Palaearctic region, as they occur only in Post-Pliocene deposits. The most important of these are the badger, glutton, elk, reindeer, chamois, goat, and sheep, which only occur in caves and other deposits of Post-Pliocene age. Camels only occur in the Post-Pliocene of Siberia (Merycotherium), although a true Cameluş of large size appears to have inhabited some part of Central Asia in the Upper Miocene period, being found in the Siwalik beds. The only exclusively Pliocene genera in Europe are Ursys, Equus, Hippopotamus, Bos, Elephas, Arvicola, Trogontherium, Arctomys, Hystria, and Lepus; but of these Equus, Hippopotamus, Bos, and Elephas are found in the Miocene deposits of India. Owing, no doubt, in part to the superior productiveness of the various Miocene beds, large numbers of groups appear to have their origin or earliest appearance here. Such are Insectivora, Felidae, Hyaenidae, Mustelidae, Ursus, Equidae, Tapirus, Rhinocerotidae, Hippopotamidae, Anthracotheridae (extinct), Sus, Camelopardidae, Tragulidae, Cervidae, Bovidae, Elephantidae, and Edentata. Groups which go back to the Eocene period, are, Primates allied to South American monkeys, as well as some of the Lemuridae; bats of the living genus Vespertilio ; Hyaenodontidae, an ancestral form of Carnivore; Viverridae; Canidae (to the Upper Eocene), and the ancestral Arctocyonidae to the Lower Eocene; Hyaenarctos, an ancestral type of bears and hyaenas; Anchitheridae, ancestral horses, to the Middle Eocene; Palaeotheridae, comprising numerous generalised forms, ancestors of the rhinoceros, horse, and tapir; Suidae, with numerous generalised forms, to the Middle Eocene; Anoplotheridae and Xiphodontidae, ancestral families of even-toed Ungulates, connecting the ruminants with the swine; and lastly, several groups of Rodents, and a Marsupial, in the Upper Eocene. We thus find all the great types of Mammalia well developed in the earliest portion of the tertiary period; and the occurrence of Quadrumana, of the highly specialized bats (Vespertilio), of various forms of Carnivora, and of Ungulates, clearly differentiated into the odd and even-toed series, associated with such lower forms as Lemurs and Marsupials—proves, that we have here hardly made an approach towards the epoch when the mammalian type itself began to diverge into its various modifications. Some of the Carnivora and Ungulates do, indeed, exhibit a less specialised structure than later forms; yet so far back as the Upper Miocene the most specialised of all carnivora, the great sabretoothed Machairodus, makes its appearance.
The Miocene is, for our special study, the most valuable and instructive of the Tertiary periods, both on account of its superior richness, and because we here meet with many types now confined to separate regions. Such facts as the occurrence in Europe during this period of hippopotami, tapirs, giraffes, Tragulidae, Edentata, and Marsupials—will assist us in solving many of the problems we shall meet with in reviewing the actual distribution of living forms of those groups. Still more light will, however, be thrown on the subject by the fossil forms of the American continent, which we will now proceed to examine.
THE discoveries of very rich deposits of mammalian remains in various parts of the United States have thrown great light on the relations of the faunas of very distant regions. North America now makes a near approach to Europe in the number and variety of its extinct mammalia, and in no part of the world have such perfect specimens been discovered. In what are called the “Mauvaises terres” of Nebraska (the dried-up mud of an ancient lake), thousands of entire crania and some almost entire skeletons of ancient animals have been found, their teeth absolutely perfect, and altogether more resembling the preparations of the anatomist, than time-worn fossils such as we are accustomed to see in the museums of Europe. Other deposits have been discovered in Oregon, California, Virginia, South Carolina, Texas, and Utah, ranging over all the Tertiary epochs, from Post-Pliocene to Eocene, and furnishing a remarkable picture of the numerous strange mammalia which inhabited the ancient North American continent.
North AMERICA—Post-PLIOCENE PERIOD.
Insectivora.—The only indications of this order yet discovered, consists of a single tooth of some insectivorous animal found in Illinois, but which cannot be referred to any known group.
Carnivora.-These are fairly represented. Two species of Felis as large as a lion; the equally large extinct Trucifelis, found only in Texas; four species of Canis, some of them larger than wolves; two species of Galera, a genus now confined to the Neotropical region; two bears, and an extinct genus, Arctodus; an extinct species of racoon (Procyon), and an allied extinct genus, Myaophagus—show, that at a very recent period North America was better supplied with Carnivora than it is now. Remains of the walrus (Trichechus) have also been found as far south as Virginia. Cetacea.—Three species of dolphins belonging to existing genera, have been found in the Eastern States; and two species of Manatus, or sea-cow, in Florida and South Carolina. Ungulata-Six extinct horses (Equus), and one Hipparion; the living South American tapir, and a larger extinct species; a Dicotyles, or peccary, and an allied genus, Platygonus ; a species of the South American llamas (Auchenia), and one of a kind of camel, Procamelus; two extinct bisons; a sheep, and two musksheep (Ovibos); with three living and one extinct deer (Cervus), show an important increase in its Herbivora. Proboscidea.—Two elephants and two mastodons, added to this remarkable assemblage of large vegetable-feeding quadrupeds. Rodentia.-These consist mainly of genera and species still living in North America; the only important exceptions being a species of the South American capybara (Hydrochaerus) in South Carolina; and Praotherium, an extinct form of hare, found in a bone cave in Pennsylvania. Falentata.-Here we meet with a wonderful assemblage, of six species belonging to four extinct genera, mostly of gigantic size. A species of Megatherium, three of Megalonyx, and one of Mylodon—huge terrestrial sloths as large as the rhinoceros or even as the largest elephants—ranged over the Southern States to Pennsylvania, the latter (Mylodon) going as far as the great lakes and Oregon. Another form, Ereptodon, has been found in the Mississippi Valley. Marsupialia.-The living American genus of opossums, Didelphys, has been found in deposits of this age in South Carolina.
Remarks on the Post-Pliocene fauna of North America—The assemblage of animals proved, by these remains, to have inhabited North America at a comparatively recent epoch, is most remarkable. In Europe, we found a striking change in the fauna at the same period; but that consisted almost wholly in the presence of animals now inhabiting countries immediately to the north or south. Here we have the appearance of two new assemblages of animals, the one now confined to the Old World—horses, camels, and elephants; the other exclusively of South American type—llamas, tapirs, capybaras, Galera, and gigantic Edentata. The age of the various deposits in which these remains are found is somewhat uncertain, and probably extends over a considerable period of time, inclusive of the Glacial epoch, and perhaps both anterior and subsequent to it. We have here, as in Europe, the presence and apparent co-existence in the same area, of Arctic and Southern forms—the walrus and the manatee—the musksheep and the gigantic sloths. Unfortunately, as we shall see, the immediately preceding Pliocene deposits of North America are rather poor in organic remains; yet it can hardly be owing to the imperfection of the record of this period, that not one of the South American types above numerated occurs there, while a considerable number of Old World forms are represented. Neither in the preceding wonderfully rich Miocene or Eocene periods, does any one of these forms occur; or, with the exception of Morotherium, from Pliocene deposits west of the Rocky Mountains, any apparent ancestor of them : We have here unmistakable evidence of an extensive immigration from South into North America, not very long before the beginning of the Glacial epoch. It was an immigration of types altogether new to the country, which spread over all the southern and central portions of it, and established themselves sufficiently to leave abundance of remains in the few detached localities where they have been discovered. How such large yet defenceless animals as tapirs and great terrestrial sloths, could have made their way into a country abounding in large felines equal in size and destructiveness to the lion and the tiger, with numerous wolves and bears of the largest size, is a great mystery. But it is nevertheless certain that they did so; and the fact that no such