SOUTH DAKOTA SCHOOL OF MINES 



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animals continue into the Upper Oligocene, the Lower Mio- 

 cene and the Upper Miocene. They are particularly 

 abundant in the Lower Miocene. Babbits occur also in the 

 Lower Miocene as well as certain poorly preserved forms 

 supposed to be related to pocket gophers. 



The number of specimens found indicates a consider- 

 able abundance of rodents in the region during Tertiary 

 time, and the number of species adds emphasis to this. It 

 happens, however, that but few complete skeletons have 

 been obtained, the best material consisting largely of skulls 

 and lower jaws, and in several of the species named, the 

 description has been based on still more fragmentary ma- 

 terial. 



The earliest specimens of the rodents obtained were 

 found by Hayden in the Big Badlands, and described by 

 Leidy. Ywth the exception of two other species described 

 many years ago by Cope, little further information became 

 available until the last few years, during which time Mr. 

 Peterson of the Carnegie Museum, and Mr. Matthew of the 

 American Museum of Natural History, each described a 

 number of species. The Carnegie Museum material has 

 come chiefly from northwestern Nebraska and eastern Wyom- 

 ing, the American Museum material from Little White river. 



Figure 33 — Skeleton of the Lower Miocene burrowing rodent Steneo- 

 fiber fossor. Peterson, 1905. 



The commonest fossil is Steneofiber. This is especially 

 abundant in the Lower Kosebud beds of Little White river 

 and in the Harrison (Daemonelix) beds in northwestern 

 Nebraska and in eastern Wyoming. Entoptychus, the 

 gopher-like rodent, seems to be fairly common in the Little 

 White river area also. Peterson found many specimens of 



