EPOREODON 



65 



Eporeodon bullatus (Leidy) 1869 

 Figs. 7, 28-30 



Original Reference: The extinct mammalian fauna of Dakota and Nebraska. Jour. Acad. Nat. Sci. 

 Phila. (2), VII, pp. 92, 106, 380 (Oreodon bullatus). 



Synonym: Merycoidodon bullatus Hay 1902. 



Type Localities: Badlands of South Dakota (HT) and John Day Valley, Oregon (PLT). 



Geologic Horizon: Middle and upper Oligocene (lower Brule and middle John Day). 



Types: Holotype, Cat. No. 10681 A.N.S.P., mature skull, much fractured, with one side of face broken 

 away, other side having molar-premolar teeth and part of canine. Collected by Hayden's Expedition of 1866. 

 Plesiotypes, all skulls, Cat. Nos. 10146 and 12299 Y.P.M., and Cat. No. 611 A.M.N.H. 



Specific Characters: The skull agrees in general form, in size, and in details of structure 

 with that of Merycoidodon culbertsonii, except for the large, inflated auditory bulla;, which approach 

 in size those of E. major. In the John Day forms the skull is more robust, with a greater expansion 



Fig. 28.— Eporeodon bullatus (Leidy). Skull. PLT. Cat. No. 12299 Y.P.M. 1/2 nat. size. 



of the zygomata. This may be due to sex or to the difference in geologic time. The muzzle is gently 

 depressed. The malar is deep beneath the orbit, while the squamosal part of the zygoma is lighter 

 and rises markedly above the glenoid surface. The nasals are wide, of nearly uniform width, and 

 posteriorly acute. The lacrimal bone has the form of that in Merycoidodon, but the lacrimal fossa 

 is relatively smaller and shallower. The frontals are wide and moderately flat and extend in 

 advance of the lacrimals. The orbits are large and look chiefly sidewise. The temporal ridges 

 unite just back of the narrow postorbital constriction. The sagittal crest is high and thin and about 

 one-third of the length of the skull. The supraoccipital crest is unusually well produced aft, with 

 the small wings moderately widespread. The brain case is narrow and has prominent lateral con- 

 vexities. The external auditory meatus is upwardly directed. The palate is wide and moderately 

 vaulted, with the palatonarial border well back of the last molars. The basicranial axis is steep. 

 The glenoid articular surface is transversely long and is shallowly convex anteroposteriorly. The 

 postglenoid process is robust and slightly more than half as long as the glenoid surface. The 

 paroccipital process is in contact with the bulla and is not appreciably flattened anteroposteriorly. 

 Index: 0.63 (based on Cat. No. 12299 Y.P.M. ). 



Foramina: The infraorbitals lie above the anterior part of P 3 . The supraorbitals are 17 mm. 

 apart. The foramen rotunda in is present. Osborn and Wortman (1894, p. 218) described it as 

 follows: 



The joramen rotundum is represented by two very minute vestigial foramina; at the sides of the pterygoid 

 plate, between the sphenoidal fissure and the "foramen ovale." It is more than probable that these will be found 

 wanting in many specimens of this species. In our specimen they certainly could not have been functional, and 

 there can be little doubt that the superior maxillary nerve made its exit through the sphenoidal fissure. The 

 foramen rotundum therefore may be said to be practically absent. 



