FOSSIL RODENTIA 35 



ISCHYROMYID^ 



Extinct. Eocene and Oligocene. 



These were Rodents with teeth more or less like Squirrels, 

 but with skulls more like those of Porcupines and Beavers. 

 They are more ancient than any living rodent families, for they 

 were common in the Lower and Middle Eocene, while no other 

 rodents appear until the Upper Eocene. Several skulls and parts 

 of skeletons of Ischyroinys, Parainys etc. are on exhibition. 



Castoroidid^. 



Extinct. Pleistocene. 



Intermediate between beavers and hystricomorphs, but of 

 very large size. Castor ohioensis equalled a black bear in size. 

 A skull and jaw of this rare animal are shown in wall case No. 

 8. Its remains are usually found in bogs, along with those of 

 the mastodon. 



South American Rodents. 



All the extinct and most of the living Rodents of South Amer- 

 ica belong to a division more nearly related to the porcupine 

 than to anything else. Some of the living ones, as the Paca and 

 Capybara are of quite large size. 



A series of skulls and jaws of extinct rodents from the Miocene 

 of South America is exhibited in the table-case. 



There are certain extinct European Rodent families which are 

 thought to be more nearly related to the South American Rodents 

 than to any others, and the remains of several of these forms are 

 exhibited in the case for comparison beside them. 



Leporid^. Hares and Rabbits. 



In the White River Badlands remains of fossil Hares are very 

 abundant. They are more primitive than the modem species in 

 the construction of the teeth, and are placed in the genus Palcc- 

 olagics ("Ancient Hare"). In the later formations of America 

 the rabbits belong to the modern genus Lepus. 



