324 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



molars. The Wasatch genus {'\Systemodon) is the most ancient 

 member of the series yet discovered. Dating from the Eocene 

 immigration, the tapirs are to be regarded as a North American 



Fig. 170. 



■ Head of the White River tapir (t Protapirus validus). Restored from a skull 

 in the museum of Princeton University. 



family, for there is here a complete continuity from the lower 

 Eocene to the Pleistocene, while in Europe they first appeared, 

 probably by migration from North America, in the middle 

 Oligocene. 



In South America the history of the tapirs is even shorter 

 and less eventful than that of the horses ; the latter, as we 

 have seen, reached the southern continent in the Pliocene 

 and there gave rise to a number of peculiar and characteristic 

 genera, but the tapirs have been found only in the Pleistocene 

 of Argentina and Brazil and only the modern genus is repre- 

 sented. 



Wofully broken and incomplete as the developmental his- 

 tory of the tapirs still is, the fragments are nevertheless suffi- 

 cient to show a mode of evolution differing in certain important 



