514 LAND MAMMALS IN THE WESTERN HEMISPHERE 



evidence. It remains to be proved whether the assemblage 

 of hoofed mammals, as a whole, was of single or multiple origin. 

 Have all ungulates been derived from a common stock, or did 

 they arise independently from several groups of clawed mam- 

 mals ? While the records cannot be followed back to the point, 

 or points, of origin of the various orders, yet it is a noteworthy 

 fact that, between several of them, the differences grow less 

 marked as the more ancient members are reached, as though 

 they were converging to a common term ; others again show 

 little such approximation, and the most probable conclusion 

 from the evidence now at hand is that the ungulate assemblage 

 is composed of several independent series. 



One such series is that of the Hyracoidea and Proboscidea, 

 to which Dr. Schlosser has given the name '^Subungulata," 

 and has pointed out its relationship to the fCondylarthra, 

 which, however, is not a close one and may be illusory. 

 Another apparently natural group is that of the peculiarly 

 South American forms, the fToxodontia, with its four sub- 

 orders, the fLitopterna and the fAstrapotheria, which all 

 appear to be traceable to closely allied families in the Eocene, 

 whose teeth strongly suggest derivation from the fCondy- 

 larthra ; but the material does not permit any positive state- 

 ments. The Artiodactyla and Perissodactyla have so many 

 similarities that they have always been regarded as closely 

 related groups, but the distinction between them was almost as 

 sharply drawn in their most ancient known members as it is 

 to-day, and there was no distinct tendency to converge back 

 into a common stem. Their mutual relationships are thus ob- 

 scure, but the Perissodactyla, at least, seem to be derivable from 

 a fcondylarthrous ancestry. 



The fCondylarthra, as a whole, were by far the most 

 primitive of the ungulates, which they connected with the 

 clawed mammals. None of the genera yet discovered can be 

 regarded as ancestral to any of the higher orders, but it is en- 

 tirely possible that in the upper Cretaceous period the f Con- 



