108 The Badland Formations of the Black Hills Region 



OREODONTIDAE 



The Oreodontidae include the commonest fossil mammals 

 of the badland formations of the Black Hills region. Repre- 

 sentatives of the family are found only in North America. They 

 originated in the Eocene, ranged through the Oligocene and 

 Miocene and became extinct in Lower Pliocene. They are 

 distinguished by many primitive characters and according to 

 Cope they constitute one of the best marked types of Mammalia 

 the world has seen. They occupy a position somewhat inter- 

 mediate between the ruminants (cud-chewing animals) and the 

 suilline pachyderms (pig-like thick-skinned animals). 



The skull, Plates 43 and 44, has to some extent the form of 

 the present day peccary. The cranial portion is much like that of 

 the camel. The skeleton as a whole more nearly resembles that of 

 the pig, but the number, general proportions, relative position and 

 plan of construction of the teeth are more nearly those of the 

 ruminants and it is this relationship to the ruminants that has 

 governed the classification of the family. Leidy in his descrip- 

 tion of the Oreodon suggested that it might very appropriately 

 be called a "ruminating hog." One remarkable feature is the 

 highly developed canine teeth in both jaws. These teeth or 

 tusks are three sided with rounded borders, the upper pair 

 curving forward, downward and slightly outward, the lower 

 pair nearly or quite straight and pointing upward, forward, and 

 outward. They give to the jaws something of the appearance 

 of the wolf's jaws but it is only a resemblance and does not 

 indicate any close relationship. As in the pigs the eyes were 

 small, the neck and legs short. With the exception of the older 

 forms all of the Oreodontidae had four toes on each foot. These 

 represent the second, third, fourth, and fifth of five toed animals. 

 Agriochoerus and the far commoner Oreodon had five on the 

 front feet. The tail was long and slender. The animals varied 

 considerably in size but the common forms were about the size 

 of the peccary. 



Following is a list of the species found within the Black 

 Hills region : 



Lower Oligocene. 



Oreodon (Merycoidodon) hybridns Leidy. 

 Oreodon (Merycoidodon) affinis Leidy 

 Oreodon (Merycoidodon) bullatus Leidy 



Middle Oligocene. 



Agriochoerus antiquus Leidy. 



