THE EOCENE OF EUROPE AND NORTH AMERICA 133 



smaller, very progressive Bridger form Stylinodon first appears; this animal 

 is distinguished by the long-crowned grinding teeth, beginning to grow 

 from persistent pulps. 



Little change appears among the Insectivora, since all the Wasatch 

 families and genera survive or pass into more advanced mutations or stages. 

 It is noteworthy that ipembers of the supposed insectivore genus Hyopsodus 

 attain a large size at this time and are the most abundant of Wind River 

 mammals. 



The opossums, or Marsupialia-Didelphyidse, are possibly represented 

 at this time in the species Peratheriimi comstockii recorded by Loomis, or 

 in the problematic form Didelphodus. 



Of the ancient Carnivora the Creodonta are now represented by three 

 families: (1) the Mesonychidse, including the giant Pachycena; (2) the 



Fig. 44. — The Lower Eocene creodont Oxywna preying upon the earcass oi Eohippus. 

 After original by Charles R. Knight in the American Museum of Natural History. 



Hysenodontidse, which are still limited to two animals about the size of the 

 fox, namely, Sinopa, the creodont most widespread geographically of any 

 geologic period, and Tritemnodon, both animals possessing slender bodies 

 and long and slender heads; (3) among the Oxyaenidae is one species of 

 Oxycena of intermediate size, and there first appear in this family at this 

 time the primitive Limnocyon and the specialized short-faced Patriofelis. 

 The latter animal is cat-like, large-limbed, nearly as large as the South 

 American jaguar {Fells uncia), and becomes especially characteristic of 

 Middle Eocene, or Bridger times. The bear-creodonts, or arctocyonids, are 

 doubtfully represented in the Wind River and Huerfano depositions. 



Progressive mammals. — The report by Cope of the existence of bats, 

 or Cheiroptera, is an error; there are no certainly known bats in the entire 

 American Tertiary. The supposed Middle Eocene (Bridger) bats reported 

 by Marsh are talpoid insectivores.* 



' Matthew, W. D., The Carnivora and Insectivora of the Bridger Basin, Middle Eocene. 

 Mem. Amer. Mus. Nat. Hint., Vol. IX, Pt. 6, 1909. 



