THE PLIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 355 



Rhinoceroses, 3-4 phyla 

 Teleoccrine 

 Acerathcrine 

 Peraceras 

 Aphelops 

 Aceratherium 

 Tapirs 



Tapiravus 

 Gravigrade edentates 



? Megalonychids 

 Last oreodonts, 2 phyla 

 Merycoclioerus 

 Merychyus 

 Camels, llamas 

 Browsing camels 



Alticamelus 



Grazing camels 



Procamelus 



Pliauchenia 



Cavicornia 



Neotragocerus 

 Merycodonts 

 Merycodus 

 Pro-Cervids 



Blastomeryx 

 Peccaries 



Prosthennops 

 Carnivores 

 Rodents 

 Mylagaulids 



(Horned gophers) 

 Primitive beavers 

 (Eucastor, Dipoidesf) 



For the first time in the history of the North 

 American continent true antelopes are positively 

 recognized, which appear to be related to the 

 tragocerine, or fiat-horned group, ^ characteris- 

 tic of the European Miocene and Pliocene; 

 hence the animal is named Neotragocerus and 

 the zone in which it occurs the Neotragocerus 

 Zone. The horn cores are perfectly straight, 

 and of a round-oval section; they approach 

 those of the existing mountain sheep (Oream- 

 nos) but lack the curvature. The teeth and 

 jaw of species of Bison also occur in this forma- 

 tion, but there is some doubt as to whether they 

 are properly associated with this geological 

 level, because the specimens may be intruders 

 from a more recent formation. 



Another possible newcomer is indicated by 

 the presence of gravigrade edentates represented 

 by an undetermined member of the Megalonyx 

 family. It will be recalled, however, that the 

 claw of a gravigrade edentate has been found 

 in the Middle Miocene (Mascall) of Oregon, 

 and there is a possibility that these giant sloths 

 may have been resident in the forests of North 

 America throughout the Caenozoic period, while 

 not finding their way into the river and flood 

 plain areas. 



By far the most astonishing feature of the 

 fauna is the extraordinary richness and variety 

 of the horses; these are the most abundant 

 animals in this formation. The four or five 

 main phyla are the same as those in the Upper 

 Miocene (p. 297), that is, we find remains of 



the conservative and presumably tridactyl 

 browsing or forest horses (Hypohippus and Parahippus) intermingled with 

 those of the intermediate stage in the evolution of the true horses (Mery- 

 chippus). There are also several species belonging to the Protohippus and 

 Pliohippus phyla, as well as several species of the desert-living horses 

 (Neohipparion). This assemblage of conservative and progressive types 

 of horses was certainly one of the most distinctive features of Lower Plio- 



' In the tragocerine group the horn cores are laterally compressed, as in the goats (caprine 

 section), but the grinders are short-crowned, resembling those in the brachyodont antelopes. 

 (Flower and Lydekker, An Introduction to the Study of Mammals Living and Extinct, Lon- 

 don, 1891, p. 349.) 



