1 66 STUDIES FOR STUDENTS 



Loup Fork Protohippus 



Hipparion 



Deep River Desmatippus 



Anchitherium 



John Day Mesohippus 



White River Mesohippus 



Uinta Epihippus 



Bridger Pachynolophus 



Wasatch Hyracotherium 



Paleotherium 



Puerco Condylarthra 



The earliest of the horses must have presented a very dif- 

 ferent appearance from the horse as we know it. They were 

 scarcely larger than a small dog and had rather the appearance 

 of one than of a horse. The Miocene members of the group 

 were about the size of a small pony, with very delicate limbs. 

 According to Osborn, they were, in all probability, marked 

 very much like the zebra. The Anchitherium, Hipparion, and the 

 earliest true horses were somewhat smaller than the recent horse, 

 but could not have been very different in their external appear- 

 ance. 



Paleotheridae . — This is the more primitive of the two fami- 

 lies. It is known only from the Upper Eocene deposits of 

 Europe, but there are several closely related later forms both in 

 Europe and America. Anchitherium and Pachy7iolophus, described 

 among the Equidae, are by some authors regarded as more closely 

 related to the Paleotheridae. 



Paleotherium, from the Upper Eocene of the Paris Basin, is 

 the typical genus. The dentition is complete, but the premolars 

 have assumed the appearance of molars. There were three toes 

 on each foot, all reaching to the ground. The surfaces of the 

 teeth are covered with enamel and have not begun to show the 

 "lakes " of cement that characterize the teeth of the true horses. 

 The largest, from P. magnum, was about the size of a rhinoceros. 

 The Tapiroidea has the two families Tapiridae and Lophiodofi- 

 tidae. In common with the other Perissodactyls, they seem to 



