Cope.] ^b [Feb. 21, 



ON THE SHORT FOOTED UNGULATA OF THE EOCEXE OF 



WYOMING. 



By Edward D. Cope. 



(Bead before the American Philosophical Society, Feb. 2\st, 1873.) 



In no group of Mammalia have the determinations of palaeontology 

 been more significant than in the Ungulata. Here, in an especial manner, 

 the anticipations of science have be^n realized, in the filling up of the 

 numerous gaps in the series of living forms. Here especially is it evi- 

 dent, that the existing fauna is but a fragment, and that the faunae of 

 the past, as we know them to-day, are but the precursors of what we may 

 bring to light to-morrow. 



The primary range of variation in the structure of the Ungulata, has 

 been generally admitted by zoologists to be found in the structure of the 

 limbs and feet. Three most prominent types have been distinguished on 

 this basis, viz. : the Artiodactyla, Perissodactyla and the Proboscidia : 

 with some of the lesser importance, those of the Toxodontia and Ilyra- 

 coidea* If we direct our attention to the detailed structure of the feet, 

 or of the teeth, each division offers its own range of variation ; witness 

 in the Artiodactyles the differences between the Ruminantia and Omni- 

 vora, and in Perissodactyla, between Equus and Rhinocerus. In either 

 order canines and incisors may be present or absent, and molars assume 

 a great variety of patterns of enamel plication. The toes in the latter 

 i uder may vary from four to one. Nevertheless, the most diverse genera 

 are bound together by intermediate forms, often extinct. Connecting 

 Omnivora and Ruminantia come Oreodon. Merycopotamus, Tragulus, etc. 

 In Perissodactyla, Anchitherium, Pakeosyops, etc., connect the extremes. 



The Proboscidians have, on the other hand, remained until recently an 

 isolated group with but few representatives, hence its definition as an 

 order, has been more or less obscured by characters of a special nature, 

 drawn from the dentition, trunk, etc., which it has been found necessary 

 to omit in characterizing the two orders above mentioned. These charac- 

 ters are so striking in their appearance as to suggest greater systematic 

 importance than belongs to them. Thus the trunk is not more important 

 as a character of the Proboscidia, than it is of the Perissodactyla, where 

 the tapir alone possesses it. Nor are the complex molars and large tusks 

 to be regarded as a definition, for in the Phacochwrus we have molars as 

 compound as in some mastodons, huge canine teeth and no incisors below ; 

 characters very different from many Artiodactyles. Nor can we regard 

 the exclusive union of the astragalus with the navicular as a final test, for 

 in Perissodactyles the facet for union with the cuboid may be considera- 

 ble (Rhinocerus) to almost nothing (Eqttus). 



The occasion for this discussion is presented by the discovery by the 



* Vide GUI, Arrangement of the Families of Mammals, Smithson, Misc., Coll., 1872, No. 2'50; 

 the best analysis of the Mammalia yet published. 



