FOSSIL RODENT/A 33 



Species of rodents than of all the other mammals put together, 

 and they are found in all sorts of places ; some are terrestrial, 

 others arboreal, others fossorial or subterranean, others am- 

 phibious. They live chiefly on vegetable food, such as grasses, 

 fruit and nuts. 



During the Tertiary period Rodents were probably equally 

 numerous; but their remains are so small that they are apt to 

 escape the attention of collectors. Even so they are among the 

 most common of fossil mammals. Alost of them belong to 

 families still living. 



MuRiD.^. Rats, Mice, Muskrats, Meadow-mice etc. 



This is the largest group of the Rodents ; there are more than 

 170 recognized species in North America alone. Several species 

 have been found rather abundant in the American Badland 

 formations. In the White River beds, Euinys, allied to the 

 White-footed Mouse, is common ; Paciciilus, allied to the Wood- 

 Rat, is found in the John Day beds ; Muskrats and Meadow-mice 

 occur in the Pleistocene. 



Geomyid.-e. Pocket Gophers. 



Found only in North America. Fossil Pocket Gophers occur 

 in the John Day and later formations in the Western States. 



Heteromyid.-e. Pocket Mice. 



Found only in North America. Fossil Pocket Mice are 

 rather common in the White River and John Day formations. 



SciURiD.^. Squirrels, Prairie Dogs, Woodchucks etc. 



Fossil Squirrels, not easily distinguishable from the modem 

 forms, are found in the Oligocene and later formations of the 

 United States. Prairie-Dogs occur in the Pleistocene. 



Haplodontiid.-e, or Sewellels. Oligocene to Recent. 



The Sewellel, or Mountain Beaver, is a peculiar little burrow- 

 ing Rodent found only in the western Coast Region of North 



