JR. S. Lull — The Evolution of the LLorse Family. 181 



15 



PLIOCENE PERIOD. 



It is probable that the later species of Pliohippus were Plio- 

 cene in distribution ; certainly Hipparion of the Old World 

 was, while during this period the true one-toed horses, Equus 

 and the curious South American Hippidion, first appear. 

 The latter is supposed by some to be a descendant of Pliohip- 

 p>us, but this is a matter of doubt. In the 

 Siwalik beds of India is found a one-toed 

 Hipparion, and it has been suggested that the 

 modern zebras may be the living descendants 

 of this genus. It is certainly not in the line 

 to the common horse, Equus caballus. 



Hippidion was extremely short-legged, with 

 a large head and curiously elongated nasal 

 bones, which together with the position of the Fig. 15. Up- 

 eyes must have given the creature a very pecu- per mo^ar tooth 

 liar cast of countenance. The teeth resembled a ffine Leidy: 

 those of PlioJdppus but were larger and of a pr, protocone. 

 more intricate enamel pattern. Hippidion was Two-thirds nat- 

 evidently much specialized and does not seem to £^i T 26 ng ~ 

 have survived the time of the deposition of the 

 Pampas beds in Ecuador, Brazil, Bolivia, and Argentina, 

 where it is found. 



16 



Fig. 16. a, Fore foot and b, hind foot of Equus caballus. One-eighth 

 natural size. (After Marsh.) 



