700 



PROTOUNGULATES 



XXVIII. 3- 



3. Classification (cont.) 



*Order 3. Litopterna. Palaeocene-Pleistocene. S. America 

 *Thoatherium, Miocene; *Macrauchenia, Pleistocene 



*Order 4. Astrapotheria. Eocene-Miocene. S. America 

 *Astrapotherium, Oligocene-Miocene 



Order 5. Tubulidentata. Pliocene-Recent 



Orycteropus, aardvark, Cape ant-eater, Africa 



Fig. 468. Skeleton of *Phenacodus as found in the rock. 

 (Simplified after S. Woodward and Cope.) 



4. Superorder Protoungulata 



*Order Condylarthra 



This group includes animals so close to the central eutherian stock 

 that it is still disputed whether some of them should be classified as 

 insectivores, primates, or creodonts. Five families are recognized, all 

 from the Palaeocene and Eocene periods. The more 'primitive' in 

 structure, such as the Eocene *Hyopsodus, had a complete row of 

 bunodont, quadritubercular teeth, and also short legs with clawed 

 digits. They were small (1 ft long) and perhaps arboreal, and there- 

 fore could be classified with lemurs or insectivores. *Mioclaenus is 

 an even older type, which possessed sharp-cusped teeth. *Phenacodus 

 (Fig. 468) is perhaps the best known condylarth. It was an Eocene 

 form with ungulate characters already present, including hoofs and 

 square bunodont molars. The build was, however, still that of a 

 generalized carnivorous or insectivorous mammal, with a markedly 



