HISTORY OF THE PERISSODACTYLA 



325 



respects from that followed by the horses or ftitanotheres. 

 Certain features are common to all three groups, such as the in- 

 crease in size and in proportionate stoutness from stage to stage 



A 



,-6^4 



Fig. 171. — Upper teeth, left side, of tapirs, showing comparative sizes. A, \ Prota- 

 pirus validus, White River Oligocene. B, Tapirus terrestris, modern. iS, external 

 incisor, c, canine, ml, first molar. 



and the gradual enlargement and complication of the pre- 

 molar teeth. On the other hand, the tapirs have been very 

 conservative, and they underwent far less radical changes 

 than did either of the other families. Aside from the pro- 

 boscis and the modifications of the skull which the develop- 

 ment of that organ necessitated, these animals remain to-day 

 very nearly what they were in Oligocene times. This, then, 

 is an example of development practically restricted to a few 

 organs, while all the other parts of the structure changed but 

 httle. 



The extinct jlophiodonts, hke the tapirs, of which they would 

 seem to have been near relatives, are known only from incom- 

 plete material, and comparatively little has been learned regard- 

 ing their history. While they were abundant and varied in 

 Europe, during the Eocene epoch, they never were a striking 

 or prominent element among the mammals of North America, 

 where they persisted one stage later, and they did not reach 

 South America. In North America they are found from the 

 Wasatch to the White River. 



