352 THE AGE OF MAMMALS 



introduced by A. planiceps of the Middle Miocene, and extending into the 

 brachyccphalic Peraceras superciliosus of the Lower Phocene; in the latter 

 animal the premaxillaries are weak and there are no superior canines; the 

 hornless and pointed nasals resemble those of the aceratheres of Europe. 

 (5) The most distinctively Old World form constitutes a fifth phylum; 

 this is composed of the short-footed ' Teleocerine ' (Teleoceras) rhinoceroses 

 which now attain very large dimensions; the males are armed with horns 

 placed at the very tip of the nasals; there is no evidence of the furth(^r 

 evolution of the second or median frontal horn, which is observed in the 

 Middle Miocene ancestor, T. medicornutus; although distributed over the, 

 entire northern hemisphere, these animals were clumsy, slow-moving, and 

 resembled the hippopotamus in their proportions; it is not improbable that 

 they largely frequented the sluggish rivers of the period. 



Tapirs. — Tapirs still survive, but are very little known, being repre- 

 sented by the single species Tapiravus rarus. 



Even-toed mammals. — The artiodactyls of the period include the sur- 

 viving oreodonts, the browsing and grazing camels, the ancestral American 

 cervids, the merycodonts, and the peccaries. 



Among the camels, Pliauchenia, an animal characterized by the presence 

 of only three premolars in the lower jaw, but in other respects showing much 

 resemblance to Procamelus, is the most typical form. The Upper Miocene 

 Procamelus is still present and abundant, and there are evidences in this 

 formation of the existence of the giraffe or browsing camels {Alticamelus) . 

 The merycodonts are still represented by Merycodus, which, it will be re- 

 called, is a delicately formed grazing type, with a skeleton analogous to that 

 of the pronghorn antelopes, but with deciduous antlers of the American 

 deer type. 



The true American procervids are represented by Blastomeryx, an animal 

 little known at this stage, but probably provided with simple, branched 

 antlers. The peccaries are represented by Prosthennops. 



Rodents. — Among the rodent fauna it is interesting to note the presence 

 of Eucastor, closely related to if not identical with Dipoides, a rodent also ob- 

 served in the Pliocene of Asia; it is possibly ancestral to the Castoroides of 

 our Pleistocene, and it should be compared with the Sigmogomphius of the 

 Pliocene of California. The peculiarly American family of Mylagaulidse is 

 now represented by Mylagaulus, a remarkable horned gopher (as discovered 

 by Matthew), and by the still more specialized Epigaidus. These animals 

 as a whole ^ seem to have been especially adapted to digging, for which 

 habit they were far better equipped than any of the existing gophers. The 

 highly modified feet and unusually small orbits suggest that they may have 

 lived almost exclusively underground. Of what use could the horns have 

 been to a burrowing rodent? They may prove to be sexual characters. 



^ Gidley, J. W., A New Horned Rodent from the Miocene of Kansas. Proc. U.S. Nat. 

 Mus., Vol. XXXII, June 29, 1907, pp. 627-636. 



