SUCCESSIVE MAMMALIAN FAUNAS 201 



it the much larger E.-fpacificus, which was inferior only to 

 E.fgiganteus and therefore the second largest of the American 

 Pleistocene horses. 



To one who knows nothing of the geological history of 

 North America it would be natural to suppose that the Pleis- 

 tocene horses must have been immigrants from the Old World, 

 which failed to establish themselves permanently here, since 

 they completely disappeared before the discovery of the con- 

 tinent by Europeans. This would, however, be a mistaken 

 inference, for North America was for long ages the chief area 

 of development of the equine family, which may here be 

 traced in almost unbroken continuity from the lower Eocene 

 to the Pliocene. On the other hand, it is quite possible that 

 some of the species were immigrants. 



Tapirs, which are now confined to southern Asia, Central 

 and South America, were not uncommon in the forested parts 

 of eastern North America as far north as Pennsylvania, but 

 they have not been found west of the Mississippi in the plains 

 region. Two species are known, a larger and heavier one, 

 Tapirus'fhaysii, and a smaller one which seems to be identical 

 with the living T. terrestris of Central and South America. 

 Like the horses, the tapirs had a long history of development 

 in North America and may well have originated here, but 

 they withdrew from the continent in the Pleistocene, probably 

 yielding to the last of the glacial advances. 



There was likewise a much greater variety of Artiodactyla 

 than North America can boast at the present day ; some were 

 autochthonous, but, for the most part, they were migrants 

 from the eastern hemisphere, where the great group of the true 

 ruminants (Pecora) passed through the greater part of its 

 development and where its headquarters still are. Indigenous 

 were the peccaries, or American swine, which still occur from 

 Texas south to Brazil. In Pleistocene time they ranged over 

 nearly all of the United States, as far northward as Pennsylvania, 

 and across the plains to the Pacific coast ; they were represented 



