66 



THE MERYCOIDODONTID/E 



Dentition: The structure of the teeth is very close to that in Merycoidodon culbertsoriii, both in 

 pattern and in size; but in one skull (Cat. No. 10146 Y.P.M.) the premolars are so crowded that 

 P 2 is obliquely set. This appears, however, to be an individual variation. The superior molar- 

 premolar index is 0.86. 



Discussion: This species holds an intermediate position between M. culbertsonii and the 

 upper Oligocene species of Eforeodon. It is, however, seemingly present in the upper Oligocene 

 of the John Day Basin, as the specimens in the Marsh Collection show, but it has changed some- 

 what from the type species. In the Great Plains area it is a transitional form, found only in the 

 upper portion of the middle Oligocene. In structure it was likewise intermediate in that the foramen 



Fig. 29. — Eforeodon bullatus (Leidy). Right half, inferior view of skull. PLT. Cat. No. 12299 Y.P.M. 1/2 nat. size. 



Fig. 30. — Eforeodon bullatus (Leidy). Right half, superior view of skull. PLT. Cat. No. 12299 Y.P.M. 1/2 nat. size. 



rotundutu was present, although probably not functional. The bulla? are much more inflated than in 

 Merycoidodon, but not to the same degree as in most of the species of Eforeodon. Cat. No. 1228+ 

 Y.P.M. is a partial skull, referred to this species, which was collected by Dr. Hayden in Colorado; 

 while three skulls, Cat. Nos. 10146, 1 1056, and 12299 Y.P.M., are from the John Day Basin, the 

 first two from Turtle Cove and the third from Bridge Creek. These three are all more robust 

 than the type, with a greater bizygomatic diameter and apparently a higher skull index. Cat. No. 

 1 1056 is more robust than Cat. No. 12299 and may well be a male. It is also individually older. 

 These skulls tuend toward brachycephaly, as does E. occidentalism and, with the exception of the 

 latter species and E. trigonocephalies, they exhibit this trend more distinctly than do any other 

 species from the Basin. 



Eporeodon condoni Thorpe 1921 

 Figs. 31-33 



Original Reference: John Day eporeodons, with descriptions of new genera and species. Amer. Jour. 

 Sci. (5), II, pp. 104-106, figs." 6-8. 



Type Localities: Bridge Creek (HT) and Haystack Valley and Turtle Cove (PTs), John Day Valley, 

 Oregon. Referred material from Clarno Bottom and Big Bottom in the same region. 



Geologic Horizon: Upper Oligocene (middle John Day — matrix green). 



Types: Holotype, Cat. No. 1 1 ol 6 Y.P.M., well-preserved skull. Paratypes, Cat. Nos. 11029 and 12294 

 Y.P.M., skulls. 



