820 GEOLOGY 



Ruminants. Much more important was the immigration of 

 the modern ruminants. Certain branches of the ruminants had 

 been represented previously, but the great ruminant group that later 

 formed so important a part of the fauna does not seem to have 

 descended from the early North American forms, but to have immi- 

 grated from Eurasia. They are first recorded in the Loup Fork 1 ><>< Is. 

 The first immigrants belonged to the deer and ox families, i 

 earliest known deer (excluding Protoceras) were from 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 deciduous antlers, fixed on long bone pedicles. About the 

 close of the period, three or four prongs were added, and in the 

 Pliocene the antlers were variously branched and the pedicles 

 shortened to insignificance, as in most living deer. This historical 

 evolution of the antlers is reproduced in the individual history of 

 the modern male deer. Born hornless, he acquires in succes- 

 years the single, the bifurcate, and the more and more complexly 

 branched antlers that mark the history of the race. It was in the 

 bifurcating stage that the deer appeared in America, its antler- 

 being simple and small, but variable. The skeletons imply light ness 

 and speed, but not to the same degree as later. 



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 

 have usually been referred to the Lower Pliocene; but Matthew 

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

 Pleistocene. 1 The earliest known bisons on the Eurasian continent 

 have been found in the Siwalik formation of India, which is regarded 

 as Lower Pliocene. 



The more primitive genera of camels had disappeared, but 1"> 

 species of more modern type have been identified from the I 

 Fork formation. The family seems to have been confined still to 

 North America. 



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

 the evolution of the horse; Anchippus, Protohippus, / V/W/ />/>*<' 

 (Merychippus), Hipparion, and other genera flourished and de- 

 ployed into forty or more species. They were still three-toed, luit 



1 Bull. Am. Mus. Nat. Hist., Xlf, 1899, p. 74. 



