86 The Badland 1 Formations of tone Black Hills Region 



golden moles of South Africa are of this. nature. A similar 

 animal in fossil form has been found in the Upper Miocene of 

 southern South America. The peculiar geographical distribu- 

 tion of certain animals and plants of southern lands has long 

 been a source of speculation and study and this finding of a 

 fossil golden mole in South Dakota so far removed from its 

 present day and fossil relatives, adds a new feature of interest. 



RODENTIA. 



The rodents or gnawers constitute the largest order of 

 mammals. Their most prominent and universal character, the 

 dentition, shows the absence of canine teeth and the paramount 

 importance of front teeth or incisors. They appear to have 

 originated in North America in early Eocene time and to have 

 been rather rapidly distributed to the other great land masses 

 of the earth. In the Black Hills region they appear first in the 

 Middle Oligocene, ancestral squirrels, rabbits, beavers, and rats, 

 being represented. The beavers or beaver-like animals con- 

 tinue into the Upper Oligocene, the Lower Miocene and the 

 Upper Miocene. They are particularly abundant in the Lower 

 Miocene. Rabbits 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 considerable 

 abundance of rodents in the region during Tertiary time, and 

 the number of species adds emphasis to this. It happens, how- 

 ever, 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 material. The only complete restor- 

 ation of which I know is Stcneofibcr fossor by Mr. O. A. Peter- 

 son, reproduced in Figure 14. 



Figure 14— Restored Skeleton of Steneofibe?' fossor. After Peterson, 1905.. 



