MERYCOIDODON 



59 



Discussion: This species, based on a single specimen, is perhaps of equivocal status until 

 further specimens are found to confirm its position. It may represent a male, exhibiting a high 

 degree of dimorphism, but, as I have neither seen any comparable forms in the innumerable speci- 

 mens from the middle Oligocene deposits of the Great Plains nor observed any marked sex 

 dimorphism in this group, I should consider it a valid species for the present. We may think of it 

 as a robust species (or subspecies), living in the general region of western Montana, but not far 

 removed from the Great Plains M. culbertsonii, perhaps representing a localized variant of that 

 species. 



Merycoidodon platycephalus Thorpe 1921 



Figs. 25-27 



Original Reference: A new M cry cold odon. Amcr. Jour. Sci. (5), II, pp. 339-340, figs. 1-2. 

 Type Locality: Near Scotts Bluff, Nebraska. 

 Geologic Horizon: Middle Oligocene (lower Brule). 



Type: Holotype, Cat. No. 12752 Y.P.M., skull, two cervicals, three dorsals, parts of rami, and distal end 

 of radius. 



Specific Characters: The very low, wide skull is mesocephalic and somewhat smaller than 

 71/. culbertsonii fericulorum. The maximum expansion of the zygomata is just in advance of the 

 glenoid surface. The malar portion is deep, while the lighter squamosal part rises gently aft. The 

 nasal bones are posteriorly obtuse, of uniform width, and gently convex in both diameters, with the 



Fig. 25 — Merycoidodon flatycefhalus Thorpe. Skull. HT. Cat. No. 12752 Y.P.M. 2/3 n.it. size. (After 



Thorpe, 1921.) 



anterior termination lying above the incisors. The lacrimal bone has a large oval-shaped pars 

 facialis, bearing a small, moderately shallow depression. The wide frontals are markedly decurved 

 above the orbits, while the central portion is nearly flat. They extend but slightly forward of the 

 lacrimal bone. The shape of the orbits is unlike that of any other species, being oval, with the long 

 axis directed forward and upward at an angle of approximately 35° from the plane of the palate. 

 There has been no crushing or distortion of the orbital margins. These orbits are actually smaller 

 than those of M. gracilis, although the skull is considerably larger. The temporal ridges unite about 

 14 mm. aft of the postorbital constriction and are rugose throughout, as are likewise the postorbital 

 processes of the frontals. The very low sagittal crest is rugose and somewhat less than a third of 

 the skull length. The supraoccipital crest has less than the normal amount of overhang, and the 

 wings are widespread. The wide and low brain case has the usual convexities. The very small 

 bullas are joined by a ridge to the paroccipital processes, which are L-shaped, because of the deep 

 anteroexternal excavation. The small external auditory meatus is very markedly directed upward, 

 more so than in the other species of this genus. The U-shaped palatonarial border is about 5 mm. 

 aft of a line across the posterior of the last molars, while the palate is narrow and very slightly 



