156 



THE AGE OF MAMMALS 



tomorphidae, Notharctidae), both surviving from the Lower Eocene. The 

 pro-Carnivora (Miacidae) also survive from the Lower Eocene, and be- 

 come more diversified than in the Wind River, although 

 most of the genera are modified Lower Eocene forms. 

 The Rodentia still are limited to the rather generalized 

 Ischyromyidae, also surviving from the Lower Eocene 

 and becoming diversified into six genera, which may 

 prove to represent more than one family. At the very 

 summit of the Eocene the American rodents known as 

 jumping mice, or Dipodidae, are doubtfully represented 

 in the genus Protoptychus. Among the modern ungu- 

 lates, as in Europe, this is the grand epoch of the Peris- 

 sodactyla. Of these, two families only (Equidae and 

 Lophiodontidae) have relatives in Europe. Of the re- 

 maining families, the tapirs (Tapiridae), titanotheres 

 (Titanotheriidae) , two families of rhinoceroses (Hyraco- 

 dontidae, Amynodontidae), cursorial, aquatic, or amphib- 

 ious respectively, appear to be peculiar to North 

 America. 



The even-toed ungulates, or Artiodactyla, are far less 

 diversified than in Europe. They include the bunodont 

 and omnivorous Achaenodontinae {Achcenodon) , related to the entelodonts 



Characteristic 

 Mammals 



Uintatheres 



Horses 



Tapirs 



Rhinoceroses 



Titanotheres 



Lophiodonts 



Entelodonts 



Homacodonts 



Oreodonts 



Camelids 



Taeniodonts 



Tillodonts 



Insectivores 



Lemuroids 



Armadillos 



Fig. 57. — In tlic li,.:irt <,l'th.' Middle Eocene, Bndgcr liadl;uid.s <il W \ nimnt^, ii. tli.' fani.nis 

 locality known as Grizzly Buttes. Zone of Orohippus and Palwosyops. Photograph by 

 American Museum of Natural History, 1903. 



