FOSSIL VERTEBRATES— MAMMALIA 1 69 



It is found most commonly in the Loup Fork. Many teeth 

 • resembling CJialicotlierium have been named from all parts of the 

 world, notably China, Hungary, and Germany, indicating a very 

 wide range for the genus. 



From the Tertiary deposits of South America, in Patagonia, 

 and the Argentine Republic come the remains of many animals 

 that seem to be without representatives in any other part of the 

 world. In some respects they resemble the Perissodactyls and, 

 indeed, one of the orders is regarded by Zittel as a possible 

 family of that group. Their relationships are, however, still too 

 imperfectly known to permit of much discussion. Three orders 

 are known, the Typhotheria, Toxodo?itia and Litopterna {Proterothe- 

 ridae Zittel). Smith Woodward says they "must be little mod- 

 ified descendants of very primitive eutherian mammals." 



Typotheria. — The order is peculiar among the ungulates, in 

 that it possesses a well-developed clavicle. The limbs are unmod- 

 ified and the dentition is nearly complete. 



Pachyrucus and TypotJierium are the best known genera. The 

 first was somewhat the smaller of the two. The teeth are some- 

 what rodent-like in appearance and the dentition is not com- 

 plete. There was a considerable diastema between the enlarged 

 incisors and the premolars, the canines were wanting. 



Toxodontia. — The second order of the South American 

 group resembled in many of its characters the first, but lacked 

 the clavicle, and the limbs were modified toward the ungulate 

 type, there being but three toes on the fore and hind feet The 

 animals were much larger than the previous order, reaching 

 nearly the size of the rhinoceros in the genus Toxodon. The 

 bodies of the animals were short and stout, and the head was 

 placed on a very short neck low on the body. The two typical 

 genera Toxodont and Nesodon are both from the Tertiary of South 

 America, but Nesodon is from the earliest strata. 



Litopterna. — This order was much farther developed than 

 the preceding, and in general appearance could not have been 

 far from that of the modern horse. The primitive condition is 

 indicated by the complete dentition and the stage of develop- 



