188 THE AGE OF MAMMALS 



North America or first known in the Upper Eocene of that region. The 

 conspectus of this fauna is as follows: 



Among the odd-toed ungulates of this as- 

 LowER Oligocene semblage the horses (Equidse) are conspicu- 

 Grotip ous by their absence. The palieotheres (Pa- 



a. {Continued from Eocene) Iceotherium, Plagiolophus) are entering on their 

 Palteotheres decline. The rhinoceroses are represented 



Anthracotheres by a small form {Ronzotherium) with sub- 



Anoplotheres hypsodont molar teeth which appears to be 



Csenotheres of the river-frequenting, amynodont type 



Canids (dogs) rather than a true rhinoceros. Tapirs have 



Erinaceids not appeared in Europe at this stage. 



Opossums The last of the anoplotheres occur at this 



Hyaenodonts level. Among the even-toed ungulates the 



h. (New Arrivals) entelodonts, supposed migrants from America, 



Rhinoceroses ^re still rare. The anthracotheres are begin- 



Entelodonts iiing their dominant reign. These animals are 



Gelocids purely European in origin, hardy travelers 



Mustelids and versatile feeders; they are very widely dis- 



Amphicvonids tributed geographically and form valuable means 



Cricetines for time correlation. They are polyphyletic and 



(hamsters) include hypsodont and brachyodont branches 



as follows: (1) The typical Ancodus {Hyo- 

 potamus) velaunus of Ronzon, with its long-crowned molar teeth, is of the 

 same evolution stage as the animals {A. bovinus) found at Hempstead on 

 the Isle of Wight; it is a bit more hypsodont or modern than our Ancodus 

 (A. americanus, A. hrachyrhynchus, A. rostratus) of the great plains of 

 ancient Dakota. (2) The short-crowned anthracothere Brachyodus also 

 occurs in the Fayum of northern Egypt (B. goringii), in Dakota (B. 

 hrachyrhynchus), and at Hempstead. It is descended from the Catadon- 

 therium of the Lutetian. (3) Anthracotherium also occurs, an ancestor of 

 the giant Middle Oligocene forms. The anthracotheres^ also exhibit a 

 divergence into dolichocephalic and brachycephalic forms. There is a wide 

 geographic distribution of the ancodons in Europe, Africa, Asia, and 

 North America. No ancestral forms have been discovered in the Amer- 

 ican Eocene, and their abundance in the Upper Eocene of Europe and 

 Africa points to migration from the Old World; it would appear that from 

 a north Asiatic center these animals may have migrated independently to 

 Europe, southern Asia, and to North America. The American species occur 

 in four successive levels, and parallel those of Europe in their evolution. 

 Whereas in Europe they disappeared at the close of the Middle Oligocene, 

 in North America they survived to the Lower Miocene, represented by an 



' Matthew, W. D., Observations upon the Genus Ancodon, Bull. Amer. Mus. Nat. 

 Hist., Vol. XXVI, Art. i, Jan. 5, 1909, pp. 1-7. 



