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 Palzearctic 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 EZyuus 
to the Older Pliocene. In North America they are chiefly 
Pliocene, true Zquus 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, Hquus is 
the only genus, and is Post-Pliocene or at most Newer Pliocene. 
While, therefore, the ancient progenitors of the Equide were 
common to North America and Europe, in Miocene and even 
Eocene times, true horses appear to have arisen in the Palearctic 
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 were 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 general map, there is a large expanse of shallow water, 
which a moderate elevation would convert into dry land, in a 
sufficiently temperate latitude. 
