594 THE MIOCENE PERIOD 



the evolving horse to dry plains and grassy food (Fig. 497). The 

 elimination of the side toes, the lengthening of the limbs, the con- 

 centration of the limb muscles near the body to reduce the weight 

 of the parts most moved, and the consolidation of the leg bones, were 

 modifications in the interest of speed and strength. An elongation 

 of head and neck was necessary to reach the ground. The front 

 teeth were reduced to chisel-like, cropping forms, while the molars, by 

 developing ridges, became suited to grinding. The teeth also grew 

 in length to provide for the great wear caused by the dry siliceous 

 grasses. 1 It is probably as safe to infer a development of dry, grassy 

 plains from this evolution of the horse as to infer climatic and 

 topographic conditions from plants and other organic adaptations. 



Other orders. Tapirs were but meagerly represented, but 

 rhinoceroses were prominent. Most of the American species were 

 hornless, but two-horned species appeared during the period in 

 Europe. Carnivores were abundant, and had assumed forms re- 

 ferred with some doubt to the living genera. The dog family in- 

 cluded numerous wolves and foxes; the cat family, panther-like 

 animals and saber- toothed cats; weasel-like and otter-like forms, 

 and an ancestral raccoon represented another family. The genera of 

 the late Miocene were nearly all different from those of the early 

 Miocene, indicating rapid evolution. Rodents were abundant, but 

 neither insectivores nor primates are among the North American 

 fossils. The development of the plains, which favored horses, deer, 

 and cattle, was obviously unfavorable to the lemuroids. 



Primates. In the Old World, apes had appeared. One type was 

 rather large, combining some of the characters of apes and monkeys; 

 another was related to the chimpanzee and gorilla, and about as 

 large as the former. It is the view of some paleontologists that the 

 ancestral branch of the Hominida (man) must have diverged from 

 its relatives at least as early as this; but on the origin of man the 

 geologic record throws no direct light. 



Lower vertebrates. Little of moment is recorded relative to the 

 lower vertebrates. Not much is known of American Miocene birds, 

 but their advancement in later stages implies that they continued 

 their evolution with measurable rapidity, a conclusion supported 

 by the European evidence. Reptiles were represented by turtles, 

 snakes, and crocodiles. Amphibians came again to notice in the 



1 For a recent illustrated statement of the evolution of the horse, see Matthew, 

 Supplement to Am. Mus. Jour., Vol. III. 



