PETERSON: A REVISION OF THE ENTELODONTIDA 147 
Middle Miocene Ammodon ) 
| Dinohyus 
Lower Miocene 
| Deeodon Bodéchcerus 
| 
| | t; 
| leer 3 
| Pelonax [eA | 3 
: | aN \S = 
Oligocene | NE Ue a) 
| Selle = 
| SS hs Entelodon © 
| Archeotherium S 
DS é 
| See, 
| NE 
5 ee 
Eocene ) 
DIAGRAM EXPRESSING THE PHYLETIC AND GEOLOGIC PosITION oF Entelodontide. 
As Pomel (74, p. 1085), Leidy (50, p. 174), Marsh (64, p. 408), Kowalevsky 
(38, p. 450), Scott (87, p. 322), Schlosser (88, p. 80), and others have shown us, this 
family has in the pigs and Hippopotamus its nearest °' representatives of the recent 
forms, while the direct ancestors are yet to be found. In the meanwhile we have 
seen that during the relatively short geological time in which we are able to trace the 
family in Europe and America there are certain anatomical differences, indicating 
lines of divergence. These lines probably point to habits due to the varied environ- 
ments during the life-history of the group. 
We have, for example, in the European genus Hntelodon, a form with enlarged 
premolars indicating a diverging step from Archwotheriwm. It has further been 
pointed out that the base of the skull of Hntelodon is very greatly different from that 
of the American forms; and also that the trigon of the lower molars is entirely 
absent, while in Archwxotherium it is quite plain in young, but fully adult specimens. 
Pelonaa ramosum of the upper Oligocene has tremendously heavy chin-processes, a 
very prominent angle, and single-rooted first and second lower premolars. Deodon 
of the John Day formation has no chin-processes at all and has a light angle of the 
lower jaw; while in the Miocene of Nebraska we have in Dinohyus a form with 
very small chin-processes, and a gentle sweep of the downward projection of the 
angle approaching what is seen in Dwodon. The median upper incisors of Dino- 
hyus are distinctly reduced and are in fact sometimes wanting, having been perhaps 
shed quite early and the alveoli closed up. 
In confining ourselves to these characters of the mandible alone and leaving 
out Mntelodon whose generic position can hardly be doubted, it would seem that 
there is a variation of importance, when we consider the fact that all the specimens 
61 The relationship to these recent forms is a very remote one. 
