256 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



tusks ; and their skulls were so curiously modified as to bear a 

 distinct resemblance to the skull of a huge carnivore. The 

 famynodonts migrated to the Old World and occur in the 

 Oligocene of France, but the fhyracodonts would seem never 

 to have left North America. The third series, that of the true 

 rhinoceroses, comprised several genera at different levels in 



f r- 



- -v. .^_^ / y / t, — ■ »■ J, 



Fig. 135. — tHornless rhinoceros {^Ccenopus tridactylus) of the White River stage. 

 Restored from a skeleton in the American Museum. 



the White River beds (^Trigonias, '\Ccenopus, etc.) ; they were 

 of uncertain origin and it has not yet been determined whether 

 they were immigrants or of native stock. Many species have 

 been found, varying much in size, up to that of a modern tapir, 

 and not unlike one in proportions, for they were of lighter build 

 and had relatively longer legs than any existing rhinoceros. 

 The species of the lower and middle substages were all horn- 

 less, but in the uppermost substage we find skulls with a pair of 

 nasal horns in an incipient stage of development. This was the 

 beginning of the tpaired-horned rhinoceroses {\ Dicer atherium) 

 which so flourished in the John Day and the lower Miocene. 



