2 $6 GEOLOGY. 



the period, three or four prongs were added, and in the Pliocene the 

 antlers were variously branched and the pedicles were 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 successive 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 antlers being simple and small, but 

 variable. The skeletons imply lightness and speed, but a less com- 

 plete adaptation to celerity than was attained 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, while Williston refers them 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 camels, oreodons, and peccaries. — Besides the new families 

 of artiodactyls, three of the previous ones continued to flourish, the 

 camels, the oreodons, and the peccaries. Fifteen species of camels 

 have been identified from the Loup Fork formation, belonging to 

 the genera Procamelus, Protolabis, Miolabis, Oxydactylus, and Pli- 

 auchenia. The more primitive genera of the White River and John 

 Day epochs had disappeared. The more robust Procamelus and its 

 allies of the Loup Fork epoch quite distinctly foreshadowed the true 

 camels which were later to go to Asia, while the Pliauchenia fore- 

 shadowed the llamas, which were later to go to South America; but 

 the whole family seems yet to have been confined to North America. 

 The oreodons, though destined to become extinct at the close of the 

 period, were represented by 18 American species. They appear thus 

 not to have dwindled away but to have gone out suddenly, in the 

 geological sense, not unlikely from the attacks of some new carnivore. 

 They appear never to have migrated from North America. The pec- 

 caries do not seem to have been specially abundant. 



The evolution of the horse. — It was a great epoch in the evolution of 

 the horse, Anchippus,Protohippus, Pliohippus (Merychippas), Hipparion, 



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



