184 



UNGULATA 



ORDER VII 



formula : 



3.1.4.3. 



Cheek teeth selenodont. Superior molars with four, rarely with 



3.1.4.3. 



five crescents. Premolars anteriorly monocuspid, laterally compressed, slightly elongated, 

 progressively complex posteriorly. Fourth premolar sometimes molariform ; inferior 

 first premolar functioning as canine, inferior canine functioning as fourth incisor. 

 Radius, ulna, carpals, tarsals and metapodials distinct. Feet tetradactyl; in more 

 primitive forms, a small pollex in the fore foot. 



The Agriochoeridae (Oreodontidae) are extinct and at present are known only 

 from the Eocene, Oligocene, Miocene and Pliocene of North America. They 

 have transmitted no descendants to recent times, but probably may be traced 

 back to the same stem-form as the Camelidae. 



Subfamily 1. Agriochoerinae Leidy. 



Superior molars with deeply concave external crescents. Humerus strongly 

 expanded distally, with low trochlea. Terminal phalanges claw-like. Tail long. 



In appearance the Agriochoerinae show great similarity to the Anoplo- 

 theriidae, from which they differ by the presence of two lateral toes. Upper 



Eocene to Lower Miocene : North 

 America. 



Frotagriochoerus Scott. Pre- 

 molars : ^. Superior molars with 

 three crescents in the anterior half 

 of the tooth. Fourth premolar 

 simple in both jaws. Upper Eocene 

 (Uinta beds) ; F. annectens Scott. 



Agriochoerus Leidy (Artionyx 

 Osborn and Wortman ; Merycopater, 

 Coloreodon Cope ; Agriomeryx Marsh) 

 (Fig. 252). Dental series broken 

 by a post-canine diastema ; without 



superior incisors. Premolars : — . 



Posterior premolar above and below like first molar. Superior molars with 

 four crescents and concave distinctly W-shaped ectoloph. Orbits open 

 posteriorly. Pollex present. Terminal phalanges short, curved and pointed. 

 Oligocene ; North America. A. latifrons, major Leidy, A. guyotictnus Cope. 



Agriochoerus latifrons Leidy. Oligocene (White River 

 beds), Nebraska. Upper and lower cheek teeth. 3/.. 

 (After W. B. Scott.) 



Subfamily 2. Oreodontinae Leidy. 



Without long diastema. Thorax large, limbs short. Orbits generally closed 

 posteriorly. Humerus typically artiodactyl. Terminal phalanges generally developed 

 into short narroiv hoofs. 



In habit the Oreodontinae exhibit great similarity to Dicotyles; the later 

 forms often acquire similarity with Hippopotamus by the thickness and 

 prominence of the zygomatic arch. Upper Eocene to Upper Miocene ; North 

 America. 



