The geographical distribution of animals, with a study of the relations ...

142 DISTRIBUTION OF EXTINCT ANIMALS. [part 11.the American Pliocene and Miocene periods, abounding ingenera and species ; whereas in Europe the group only exists inthe Post-Pliocene or Lower Pliocene, with one Upper Miocenespecies of Camelus in N. India. The Anthracotheridae (extinct),found only in the Upper Miocene of France and India, reacheven the Lower Eocene in America.These facts may be due, in part, to a want of strictco-ordinationbetween the Tertiary deposits of Europe and North America,—in part to the imperfection of the record in the latter country.Yet it does not seem probable that they are altogether due tothese causes, because the Miocene beds, which are by far thebest know T n in America as in Europe, exhibit deficiencies of thesame kind as the less known Eocene deposits. The fossil faunaof both countries is so rich, that we can hardly impute great andwell marked differences to imperfect knowledge; yet we findsuch important families as the Civets, Hyamas, Giraffes, andHippopotami absent from America, with the Weasels, and Antelopesalmost so ; while America possesses almost all the Camelidaa,two peculiar orders, Dinocerata and Tillodontia, and four remarkablypeculiar families, Limnotheridse, Lemuravidse, Oreodontidseand Brontotheridae. If then the facts at present known representapproximately the real time-relations of the groups in questionon the two continents, they render it probable that weasels, bears,true horses, swine, oxen, sheep and antelopes, originated on theOld World continent, and were transmitted to America duringsome part of the Miocene period ;while camels originated in theNew World, and somewhere about the same time passed over toEurope. Of the extinct families common to the two hemispheres,the Anthracotheridse alone seem to have had anAmerican origin. Of the genera common to the two countries,almost all seem to have had a European origin, the only generaof equal date being the two rhinoceroses and three Anchitheridse;but if the Brontotheridse are allied to the Ehinocerotidae,these latter may have originated in America, althoughnow anexclusively Old World type. These conclusions are not improbablewhen we consider the much greater size of the OldWorld continents, extending far into the tropics and probably