218 THE AGE OF MAMMALS 



ized in their teeth to be regarded as directly' ancestral. The European 

 Entelodon of Eymar (1847) or Elotherium of Pomel (1847, indet.) is re- 

 garded as generically different from the American forms. Of the latter, 

 Archcvothcrium of the Lower Oligocene, Titanotherium Zone, is believed to 

 be distinguished from Entelodon by its elongate snout; in brief, its greater 

 dolichocephaly; the earliest phase {A. mortoni) gives rise to a series of 

 species, and already in the Upper Titanotherium Zone attains an impos- 

 ing size {A. ingens). The tul^erosities of the lower jaw are strongly de- 

 veloped in Pelonax hathrodon of the Protoceras Zone, Upper Oligocene. 

 In the Upper Oligocene of the John Day, a massive form, Boochcerus hu- 

 merosus, appears, distinguished by a long humerus and short feet, a slow- 

 moving type, while the gigantic Dinohyus hollandi of the Harrison beds of 



Fig. 106. — Type of the Oreodon Zone. Skeleton of the Middle Ohgocene oreodont Merycoi- 

 dodon (" Oreodon ") culbertsoni. In the American Museum of Natural History. 



Nebraska is more cursorial. The close of the Oligocene, or beginning of 

 the Miocene witnessed the evolution of four great phyla of entelodonts 

 (Pelonax, Dinohyus, Dceodon, Boochoerus). The distinctions of these phyla 

 require further discrimination. 



The geographic range was as far east as New Jersey (Amniodon Marsh), 

 while the geologic range is to the summit of the Arikaree beds, which are 

 here regarded as Lower Miocene. It has been suggested by Schlosser and 

 Winge that these animals were omnivorous or even carnivorous, which is 

 highly improbable. The extraordinary appearance, as sketched some 

 years ago under the direction of the present author (Fig. 76), is probably 

 less accurate than the more recent restoration by Mills under the direction 

 of Peterson (Fig. 83), in which the ears are placed lower dowTi and are 

 more drooping, in keeping with the inferior position of the external audi- 



