THE EOCENE OF EUROPE AND NORTH AMERICA 149 



Lutetian times, because no anthracotheres are knowii below this period, 

 and no similar forms are found in the Eocene of North America. None 

 of these European forms appear to include the ancestors of the true Oli- 

 gocene anthracotheres {Anthracotherium) of Europe, a case of discontinuity 

 which is parallel to that of the Eocene and Oligocene pigs. Stehhn con- 

 cludes that the anthracotheres occurring in the Lower Oligocene of Europe 

 are not autochthonous, but migrants, or "in-wanderers." Since almost 

 simultaneously similar "in-wanderers" appear in North America, we should 

 probably regard Asia as the common northern center of the true anthra- 

 cotheres ; still, we must not forget that the diminutive (Rhagatherium cegyp- 

 tiacum) form of the Fayum of northern Africa is one of the most primitive 

 anthracothere types which we know. 



Ancodonts. — Parallel with and related to the anthracotheres is the second 

 group of semi-selendont artiodactyls which, in a comprehensive sense, 

 can be embraced in the term Eocene ancodonts, or hyopotamids, distin- 

 guished liy the structure of the molar teeth, the open mesostyles, and the 

 generally sharpened crests. These Eocene ancodonts are astonishingly 

 numerous, including Mixtoiherium (brachycephalic) from Quercy, and Da- 

 crytherium (dolichocephalic), and ranging through the Lutetian, Bartonian, 

 and Ludian stages in several phyla, including beside, the above Catodon- 

 therium and Hyracodontherium. While these animals (Mixiotherium) dis- 

 appear at the close of the Eocene of Europe, Stehlin discusses the very 

 interesting question, already suggested by Scott (1890) and Earle, of their 

 possible ancestry to the group of oreodonts which suddenly appear (Eomeryx, 

 Protoreodon, Protagriochcerus, etc.) in the Uinta Formation, Upper Eocene, 

 of northern Utah, Rocky Mountains. Stehlin, however, dismisses this 

 theory, showing that, despite many resemblances, the mixtotheres of Europe 

 are too specialized to have given rise to the oreodonts. He admits the pos- 

 sibility of a north Asiatic center from which common ancestors of the 

 European mixtotheres and the American oreodonts may have wandered, 

 to give rise to the respective Old and New World forms. 



Arboreal mammals. — The Primates include the lemur-like Adapts, 

 appearing in the Lutetian, surviving through the Ludian, and reappearing 

 in the giant Megaladapis of Madagascar. There is also the Tarsius-like 

 Necrolemur, which appears in the Lutetian and survives through the Ludian. 

 Of arboreal type are also probably the sciuromorph, or squirrel-like 

 rodents (Plesiarctomys) , analogous to similar forms in North America ; it is 

 noteworthy that most Eocene rodents seem to be arboreal or forest-living 

 forms ; the plains-living forms are not known until the Oligocene. Of the 

 remaining small fauna it is important to note that among Insectivora l)oth 

 the moles (Talpidffi) and hedgehogs (Erinaceidse) first appear in the Lutetian. 

 Considering this powerful herbivorous and small fauna it is surprising 

 that we know so little of the carnivores, since these are confined to the small 

 viverroid, or Sinopa-Vike forms of the Lutetian, which are succeeded by the 



