All of the foregoing artiodactyl families were exclusively North American in Oligocene distribution; even the camels did not reach Asia till the Pliocene, and the other families never invaded the Old World at all. There were, however, two additional families, which also occurred in the eastern hemisphere, whence one of them, and possibly the other, was derived. The unquestionably Old World family, that of the †anthracotheres, was represented in the White River by two genera (†Bothriodon and †Anthracotherium), which were short-legged, long-snouted, swine-like animals, which have no near relations in the modern world. The other family, the †giant pigs, which we have already met with in the lower Miocene and upper Oligocene, is of doubtful origin, and nothing has yet been found in the preceding formations of either North America or Europe which can be regarded as ancestral to them. The White River genus (†Archæotherium) was very like the John Day and Arikaree genera, but most of the species were much smaller and some were not so large as a domestic pig. In the uppermost beds, however, are found huge species, which rivalled those of the subsequent formations. That these strange animals were rooters and diggers and therefore pig-like in habits is indicated by the manner in which the teeth are worn.
Fig. 137.—†Giant pig (†Archæotherium ingens) from the lower White River stage. Restored from a skeleton in the museum of Princeton University.
South America.—The older continental Tertiary formations of South America cannot be correlated with those of North America or Europe, because they have nothing in common. Difficult as it is to give a correct and adequate conception of the Tertiary mammalian life of the northern hemisphere to one who has not made a study of it, it is far more difficult in the case of South America. The stock of adjectives, such as “peculiar,” “bizarre,” “grotesque” and the like, already overworked in dealing with northern forms, is quite hopelessly inadequate where everything is strange. In addition to this, we are seriously handicapped in treating of the Oligocene and Eocene of South America by very incomplete knowledge. Many fossils have been collected and named, but the great majority of these are known only from teeth; a few skulls and limb-bones have been described, but no skeletons, and therefore much is very uncertain regarding these faunas.
The Deseado formation (Pyrotherium Beds) has been variously referred by different writers from the upper Cretaceous to the lower Miocene, but its most probable correlation is with the Oligocene. Though most of the mammalian groups are the same as those of the Santa Cruz, the proportions of the various orders in the two faunas are very different, but, to some extent, the difference is probably illusory and due to the conditions of fossilization, for, as a rule, the small mammals are much less frequent and well preserved in the older beds. As in the Santa Cruz, the marsupials were the only predaceous mammals, and some of them attained gigantic size; but no such variety of these beasts of prey has been found in these beds as occurred in the middle Miocene. In addition, there were numerous small herbivorous marsupials. One of the most striking differences from the Santa Cruz fauna was in the very much smaller number of Edentata, which, instead of being extremely common, are quite rare among the fossils. No doubt there was a real and substantial difference in this respect, but it was probably not so great as it seems, and the same three suborders are found in both formations. One of the few †ground-sloths that have been obtained was very large (†Octodontherium crassidens), a much larger animal than any species of the suborder that is known from the Santa Cruz. The †glyptodonts were also rare, and only two genera and species have been described from very scanty remains. Armadillos, on the other hand, were much more common, and no less than eleven genera have been named, three of which occurred also in the Santa Cruz. Among these was the remarkable genus †Peltephilus, in which the anterior two pairs of plates of the head shield were modified into horn-like spines.
Equally striking was the remarkable diminution of the Rodentia, as compared with those of the Santa Cruz, though, of course, this is an inaccurate mode of stating the truth, occasioned by the fact that we are following the history in reverse order. It would be preferable to say that the rodents underwent a remarkable expansion in the Santa Cruz. These rodents of the Deseado stage are the most ancient yet discovered in South America and represent only two families, both belonging to the Hystricomorpha, or porcupine group. If, as Dr. Schlosser and other European palæontologists maintain, the Hystricomorpha were all derived from a family of the European Eocene, this would necessitate a land-connection between South America and the Old World independent of North America, for the latter continent had no hystricomorph rodents until the connection between the two Americas was established.
The great bulk of the Deseado fauna is made up, so far as individual abundance is concerned, of hoofed animals belonging to the typically South American groups. The †Toxodonta were represented partly by genera which were the direct ancestors of the common Santa Cruz genera (†Pronesodon, †Proadinotherium), and, more numerously, by a very peculiar family, the †Notohippidæ, which had highly complex, cement-covered grinding teeth. Still a third family of this suborder, the †Leontiniidæ, was highly characteristic of the Deseado fauna and is not known from the Santa Cruz. These were large animals, with a small horn on the tip of the nose and low-crowned, comparatively simple grinding teeth. Even more abundant were the †Typotheria, small forms which were ancestral to the Santa Cruz genera, larger ones which died out without leaving successors and one quite large animal (†Eutrachytherus) which seems to have been the ancestor of the Pliocene and Pleistocene †Typotherium. This series is not known to have been represented in the Santa Cruz and may have withdrawn from Patagonia at the end of the Deseado stage.
