154 DISTRIBUTION OF EXTINCT ANIMALS. [part ii. 



early times. The true bears (Ursus) are almost the only 

 important genus that seems to have recently migrated. In 

 Europe it dates back to the Older Pliocene, while in North 

 America it is Post-Pliocene only. Bears, therefore, seem to 

 have passed into America from the Palaearctic region in the latter 

 part of the Pliocene period. They probably came in on the 

 north-west, and passed down the Andes into South America, 

 where one isolated species still exists. 



Ungulata. — Horses are very interesting. In Europe they date 

 back under various forms to the Miocene period, and true Equus 

 to the Older Pliocene. In North America they are chiefly 

 Pliocene, true Equus being Post- Pliocene, with perhaps one or 

 two species Newer Pliocene ; but numerous ancestral forms date 

 back to the Miocene and Eocene, giving a more perfect " pedi- 

 gree of the horse " than the European forms, and going back to a 

 more primitive type — Orohippus. In South America, Equus is 

 the only genus, and is Post-Pliocene or at most Newer Pliocene. 

 While, therefore, the ancient progenitors of the Equidae were 

 common to North America and Europe, in Miocene and even 

 Eocene times, true horses appear to have arisen in the Palasarctic 

 region, to have passed into North America in the latter part of 

 the Pliocene period, and thence to have spread over all suitable 

 districts in South America. They w T ere not, however, able to 

 maintain themselves permanently in their new territory, and all 

 became extinct ; while in their birth-place, the Old World, they 

 continue to exist under several varied forms. 



True tapirs are an Old World group. They go back to the 

 Lower Miocene in Europe, while in both North and South 

 America they are exclusively Post-Pliocene. They occur in 

 France down to the Newer Pliocene, and must, about that 

 time, have entered America. The land connection by which 

 this and so many other animals passed between the Old and 

 New Worlds in late Tertiary times, was almost certainly in the 

 North Pacific, south of Behring's Straits, where, as will be seen 

 by our geueral map, there is a large expanse of shallow water, 

 which a moderate elevation would convert into dry land, in a 

 sufficiently temperate latitude. 



