xxvm. s NOTOUNGULATES 701 



curved spine, small brain-case, sagittal crests, rather short limbs with 

 slightly elongated metapodials, the central digit the longest, complete 

 ulna and fibula, carpus and tarsus not interlocking, and a long tail. 

 The animal was, however, rather large (4 ft long). Smaller Palaeocene 

 phenacodonts, such as *Tetraclaenodon, still possessed claws and may 

 have been very close to the ancestry of all protoungulate types. Evi- 

 dently some 10 million years of herbivorous life in the Palaeocene had 

 produced only suggestions of the 'ungulate' facies. Other condylarths 

 became more specialized in the Eocene. Thus *Meniscotherium had 

 lophodont grinders, though retaining the clawed digits. *Didolodus 

 and similar forms from South America are condylarths that may 

 perhaps have given rise to some of the characteristic South American 

 ungulates though they themselves survived to the Miocene. The 

 # Periptychidae were Eocene condylarths probably ancestral to the 

 pantodonts. They also show similarities to the surviving Orycteropus, 

 which may be descended from them. 



5. South American ungulates 

 *Order Notoungulata 



The ungulate fauna of South America provides a case of geographic 

 isolation as striking as that of the marsupials in Australia. In Palaeo- 

 cene times there were ungulates common to South America and the 

 rest of the world. Besides the condylarths, considered above, there 

 was the *Palaeostyhps, in the Palaeocene of Asia, and the similar 

 *Notostylops found in North and South America. These earliest 

 notoungulates showed only a slight advance in size and other features 

 from the basal condylarth condition. The teeth possessed simple 

 ridges. From some such beginnings there quickly developed, after the 

 isolation of South America in the Eocene, a very rich fauna, including 

 many large animals. Specimens of these peculiar animals were first 

 collected by Darwin during the voyage of the Beagle and were later 

 described by Owen. Darwin records that their characteristics were 

 among the earliest stimuli that turned his thoughts to evolution (see 

 p. 524). A characteristic of the group was the very large tympanic 

 bulla. The brain was small and especially the cerebral hemispheres. 



As many as nine families of notoungulate can be recognized in the 

 Oligocene; after this period they became less numerous. Some of them 

 persisted throughout the Tertiary, but all became extinct in the 

 Pleistocene, after the connexion with North America was re-made and 

 competition was felt from more modern types, both ungulates and 

 carnivores. The notoungulates known as toxodonts were very large 



