THE MIOCENE PERIOD 823 



dry silicious 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. 



Tapirs and rhinoceroses. Tapirs were but meagerly represented, 

 but rhinoceroses, though the running and swimming branches had 

 disappeared, were prominent. The American species were still 

 mainly hornless (Aceratherium) , though slight indications of horns 

 appeared in one genus (Diceratherium) . Two-horned species 

 appeared during the period in Europe. 



Carnivores. The carnivores were abundant, and had assumed 

 forms referred with some doubt to the living genera Canis, Felis, 

 Mustela, and Putorius. The dog family embraced numerous 

 wolves and foxes; the cat family, panther-like animals and saber- 

 toothed cats; the Mustelidce, weasel-like and otter-like forms, and 

 an ancestral coon. The genera of the Loup Fork epoch were 

 nearly all different from those of the John Day epoch, indicating 

 rapid evolution. Other existing families of carnivores lived in 

 Europe. 



Other orders. Rodents were abundant, but neither insectivores 

 nor primates are among the North American fossils. The develop- 

 ment of the plains which favored horses, deer, and cattle, was 

 obviously unfavorable to the lemuroids. 



Primates. In the Old World, true apes had appeared. One 

 type was a rather large annectant form, combining some of the 

 characters of apes and monkeys; another was a generalized type 

 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 Hominidce must have diverged from its relatives at 

 least as early as this ; but on the origin of the Hominidce, the record 

 throws no direct light. 



The 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 con- 

 tinued their evolution with measurable rapidity, a conclusion sup- 



1 An excellent recent statement of the evolution of the horse, admirably 

 illustrated, is given by Matthew, Sup. to Am. Mus. Jour., Vol. Ill, No. 1, 

 jJan., 1903. 



