392 AN INTRODUCTION TO THE STUDY OF FOSSILS 



digit. Examples include: (a) tapirs and rhinoceroses, both 

 of which families date from the Eocene, and were present dur- 

 ing the Tertiary upon most of the continents. Both disappeared 

 from North America during the Pliocene. The rhinoceroses 

 very probably originated in North America (Fig. 163, i). 

 (b) The huge titanotheres (Figs. 163, 7 and 171), some of the 

 later members of which attained a height of eight feet and a 

 length of fifteen feet, existed during the Eocene to Oligocene. 



Fig. 172. — A restoration of the earliest known ancestor of the modem horse, 

 Eohippus, — the Dawn Horse, from the Lower Eocene (Wasatch) of western 

 North America. In size these varied from that of a cat to a small fox. Note 

 the short face (distance from eye forwards), short neck, arched back, short limbs 

 and similarly short feet, with several divergent toes upon each. (From Scott.) 



(c) The horse family dates from the Lower Eocene in both 

 North America and Eurasia. The family branched from a so far 

 undiscovered five-toed primitive ungulate, which gave rise in 



