TILLODONTIA 



44' 



a Capybara, and of much the same general appearance. Its skeleton 

 is completely known, and shows a singular combination of characters, 

 resembling Toxodon or a generalised Ungulate on the one hand, and 

 the Rodents, especially the Leporida', on the other. In the presence 

 of clavicles it differs from all known Ungulates, and in having two 

 pairs of lower incisors from all Rodents. The teeth are i^, c%,p -j. 



»> % - 24. 



From the Tertiaries of various parts of South America a number 

 of forms more or less closely allied to Toxodon and Typotherium have 

 Keen recently described, but as many of them are very imperfectly 

 known, and there is much doubt as to their generic position, it will 

 be unnecessary to refer to them further. 



It will thus be seen that, although our knowledge of many of 

 these forms is still very limited, we may trace among them a curious 

 chain of affinities, which would seem to unite the Ungulates on the 

 one hand with the Rodents on the other ; but further materials 

 are required before we can establish with certainty so important a 

 relationship, one Avhich, if true, would alter materially some of the 

 prevailing views upon the classification of mammals. 



Group Tillodontia. 



Here may be noticed a remarkable group of animals, called by 

 Marsh, Tillodontia, the remains of which are found abundantly in 



Fig. 103. — Skull of TUlotheriumfodiens. i natural size. From Marsh. 



the Lower and Middle Eocene beds of North America. They seem 

 to combine the characters of the Ungulata, Rodentia, and Carnivora. 

 In the genus Tillotherium of Marsh (probably identical with the pre- 

 viously described Anchippodus of Leidy) the skull (Fig. 193) resembled 

 that of the Bears, but the molar teeth were of the Ungulate type, 

 while the large incisors were very similar to those of the Rodents. 



The dental formula is i -§-, 



c a p f , m 



3 

 3~* 



The first pair of incisors 



