286 



THE AGE OF MAMMALS 



Fig. 140. — Skull of the typical Lower Miocene oreodont 

 Merycochwriis proprius. In the American Museum of Natural 

 History. After Matthew. 



The fossils are, how- 

 ever, less abundant 

 than in the lower ho- 

 rizon, and further ex- 

 ploration is awaited 

 with interest. As ob- 

 served on p. 277, in 

 defining these beds as 

 Lower Miocene the 

 following characteristic 

 Oligocene forms are 

 now believed to be 

 absent: Entelodon 

 (Dinohyus), Hyper- 

 tragulus, and Steneo- 

 fiber. The latter genus is replaced in Europe by the Lower Miocene 

 Chalicomys; its successors in America are perhaps the Upper Miocene 

 and Pliocene Hystricops and Eucastor. 



Especially noteworthy among the new Lower 

 Miocene mammals is Blastomeryx, a descendant of the 

 Oligocene Leptomeryx, and broadly ancestral to the 

 American deer {Mazama and Odocoileus) . This animal 

 is hornless but provided with sharp canine tusks, and 

 is in the same stage of evolution as Dremotherium of 

 the Upper Oligocene of Europe. Other new artio- 

 dactyls are the oreodonts MerycochoerussindMerychyus. 

 The former is a brachycephalic, or short-faced successor 

 of Pr ornery cochcerus, while Merychyus is a smaller ani- 

 mal which becomes extremely abundant and is es- 

 pecially characteristic of the Middle Miocene. Both 

 these oreodonts persist through the Miocene. Among 

 the tylopods or camelids the long-limbed and long- 

 necked Oxydactylus ^ again appears, a tree-browsing 

 camel with brachyodont molar teeth broadly ancestral 

 to the ' giraffe camels ' of the Middle and Upper Mio- 

 cene. The other camelid, Protomeryx, was a small, 

 rather short-limbed animal with hypsodont molars; it 

 probably gave rise to the line of camels that ended in 

 the Pleistocene with very large and long-limbed forms. 

 The peccaries are again represented in Desmathyus. 



The perissodactyl Herbivora include the chali- 

 cotheres (Moropus) and the last survivors of the 



^ Peterson, O. A., Osteology of Oxydactylus. Ann.' Carneg. Miis., Vol. II, no. 3, Feb., 

 1904. 



Lower Miocene 



?Mastodons 

 Camelids 



Protomeryx 



Oxydactylus 

 Oreodonts 



M ery cochcerus 



Merychyus 

 Pro-Cervids 



Blastomeryx 



(hornless) 

 Horses 



Parahippus 



fAltippus 

 Rhinoceroses 



Aceratherium 



Diceratherium 

 Procyonids 



Phlaocyon 

 Mustelids 



Megalictis 

 Rodents 



