28 EVOLUTION 



three-toed feet, suited, like the reindeer's, 

 for soft ground, is a good example of those 

 horses that became extinct during the Miocene, 

 leaving no descendants, and Anchitherium, 

 found both in Europe and in America, was 

 probably also on a side branch. Of the 

 Miocene period, Dr. Lull says : " This was 

 a time of continental elevation and great 

 expansion of our western prairies and a con- 

 sequent diminution of the forest-clad areas." 

 Many forms very perfectly adapted to soft 

 herbage became extinct, " but the great 

 majority were more plastic and in consequence 

 underwent a remarkable development, during 

 this period reaching the culmination in 

 numbers and kinds." 



In the Pliocene there was a wide repre- 

 sentation of the Old World genus Hipparion, 

 most of the species still three-toed. It was 

 probably derived from the American Neo- 

 hipparion, a swift, deer-like animal, about 

 forty inches in height at the shoulder. " 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 descend- 

 ants of this genus. It is certainly not in the 

 line to the common horse, Equus caballus, 

 which makes its appearance, however, in the 

 Upper Pliocene beds both of Eurasia and 



