PAROREODON 1 77 



Discussion: In most respects this species conforms to the genus Merycoides, but in the facial 

 vacuities, the greater length of the palate, the posterior obtuse shape of the nasal bones, and the 

 lengthening of the posterior part of the skull there are marked differences, as well as in the higher 

 geologic horizon. It is indeed an extreme type of Merycoides and almost entitled to subgeneric 

 rank. 



Genus PAROREODON Thorpe 1921 

 Table 1 



Original Reference, Type Locality, Geologic Horizon, and Genoholotype: Same as for 

 P. marshi. 



Genotype: Paroreodon marshi Thorpe. 



Distinguishing Characters: Skull small, high, and strongly arched, tending toward brachy- 

 cephaly; brain case very large and full, with diameter of postorbital constriction unusually great ; 

 sagittal crest low and short, with skull depressed posteriorly ; bulla; large and deep, terminating 

 inferiorly in a sharp ridge — a unique form; nasals reduced; face relatively long (approximately 

 98 mm.); facial vacuities small and placed in front of lacrimals; orbits large and highly placed; 

 frontals wide and long; malar deep; muzzle moderately narrow, tapering gradually; interparietal 

 fused; dentition brachyodont; premolars not crowded; general tooth structure similar to that in 

 Merycoides. 



Discussion: Professor Loomis (1924B, p. 14) considers Paroreodon close to Merycliyus, but 

 my own opinion is that it is a branch from the Tichole-ptus line, nearest to Merycoides but not 

 referable to that genus. 



Paroreodon differs from Merychyus mainly as follows: Skull much higher, with high point 

 farther aft and posterior part more depressed and more brachycephalic (index 0.64); face rela- 

 tively longer; brain case and postorbital constriction of greater diameter; basicranial axis much 

 steeper; malar deeper; nasals shorter; bulla; decidedly different in shape; paroccipital processes 

 straighter in profile, adhering to the bulla; much more closely and directed more forward and out- 

 ward. The dentition differs in that in Paroreodon the premolar series is longer than the average in 

 Merychyus ; the teeth are brachyodont; the face of the metacone stands at an angle of nearly 30° 

 from the paracolic, while in the other genus they are almost on a line; the outer faces of P 3 and P 4 

 are not on the same line in the Oregon form, and none of the premolars are obliquely placed; P 3 is 

 relatively narrower; the styles on the molars are heavier; M 1 is wider than long and relatively 

 smaller, while the last lobe of M 3 is relatively larger; and the construction of P 3 and P 4 is different. 



There are no contemporary John Day forms so far described comparable to Paroreodon, and 

 for comparison we have to use the Great Plains forms. Compared with Phenacoccelus we find that 

 Paroreodon has neither frontal nor occipital vacuities, is smaller, has a larger brain case, a greater 

 postorbital constriction diameter, and a much shorter and lower sagittal crest. The face is relatively 

 longer (about 50-50 in Phenacocoelus and a third longer in Paroreodon than the part posterior to the 

 orbits) and more brachycephalic, with muzzle tapering gradually in front of orbits. The skull is 

 much higher; the bulla; are distinctly different in shape; the basicranial axis is much steeper; the 

 posterior of the skull is much more depressed; and the malar is actually deeper. In the dentition, 

 Paroreodon differs much as it does from Merychyus, since the teeth of Phenacoccelus are nearer like 

 those of Merychyus than are those of Paroreodon. The styles on the molars of the latter are 

 heavier, the metacone is offset from the paracone, the premolars are not obliquely placed, the pre- 

 molar series is relatively longer, P 3 is longer than wide, and M 1 is wider than long. The opposite is 

 true in Phenacocoelus, M 2 is much more nearly square, and M 3 is half as wide as long; but in 



