S9 2 THE MIOCENE PERIOD 



essentially to their three persistent lines, exemplified by the horse, 

 the tapir, and the lowland rhinoceros. The even-toed branch also 

 had developed into modern lines. Rodents were abundant, includ- 

 ing squirrels, beavers, gophers, rabbits, etc. 



Later fauna. Elephants. A notable addition to the mam- 

 malian fauna of North America in the late Miocene, was the probos- 

 cidians. Primitive proboscidians lived in Egypt at least as early 

 as the Middle Eocene, and in Europe in the early Miocene. Ele- 

 phants reached North America in the late Miocene, and South 

 America in the Pliocene. 



Much more important was the immigration of the modern 

 ruminants. The great ruminant group that later formed so im- 

 portant a part of the fauna does not seem to have descended from 

 early North American forms, but to have come in from Eurasia. 

 Their remains are found in the Loup Fork beds. The first immi- 

 grants belonged to the deer and ox families. The earliest known 

 deer (excluding Protoceras] were in Europe. They were hornless, 

 as are their surviving relatives in Asia. By the middle of the 

 Miocene, some of the males had acquired small two-pronged decidu- 

 ous antlers. It was at this stage that they appeared in America. 

 About the close of the period, three or four prongs were added, 

 and in the Pliocene the antlers were variously branched. The 

 Miocene skeletons imply lightness and speed, but not to the same 

 degree as now. 



There is some doubt as to the precise stage to which the remains 

 of bison found in Nebraska and Kansas are to be assigned. They 

 usually have been referred to the Lower Pliocene; but Matthew 

 assigns them to the Upper Miocene, and Williston to the early 

 Pleistocene. The earliest known bisons on the Eurasian conti- 

 nent were found in the Siwalik Lower Pliocene formation of India. 



The earlier genera of camels were gone, but 15 species of more 

 modern type have been identified from the Loup Fork formation. 

 The family seems to have been confined still to North America. 



Evolution of the horse. The Miocene was a great epoch in the 

 evolution of the horse; Anchippus, Protohippus, Pliohippus (Mery- 

 chippus), Hipparion, and other genera flourished, and forty or more 

 species. They were still three-toed, but the two lateral toes were 

 dwarfed and did not usually touch the ground, while the central one 

 was strengthened and bore all the weight. A large group of struc- 

 tural features were being modified concurrently with the feet, to fit 



