MKSOREODON 



103 



The supraoccipital crest is lower and more prolonged than in the genoholotype. The brain case is 

 moderately low and small. The external auditory meatus is tubular and like that in the other 

 species but is situated slightly lower. The U-shaped palatonarial border lies just behind the last 

 molars, and the palate is wide and gently uparched. The basicranial axis is shallow. The bullse 

 are mediumly large. The postglenoid process is stout and the paroccipital process long and slender. 

 Index: 0.63. 



Mandible: The symphysis is strong, gently sloping, and nearly straight in profile — less con- 

 cave than in M. chelonyx. The symphysiodental angle is about 40°. There is a tubercle at the 

 inferior part of the symphysis. The ascending ramus is rather deep, with the angle strongly 

 marked. The coronoid process is short and somewhat slender. The sigmoid notch is shallow and 



Fig. 66. — Mesoreodon megalodon Peterson. 

 Fragmentary skull and jaw. HT. Cat. No. 1325 

 CM. 3/8 nat. size. (After Peterson, 1906.) 



Fig. 67. — Mesoreodon megalodon Peterson. 

 Mandibular ramus. PLT. Cat. No. 1323 CM. 

 3/8 nat. size. (After Peterson, 1906.) 



wide open, and the condyle is set but very slightly inward from the posterior edge of the ascending 

 ramus. In M. chelonyx the condyle is much farther from the line of the posterior edge of this 

 ramus. The masseteric fossa is about as extensive as in the latter species. 



Foramina: The infraorbitals lie above the middle of P 3 . 



Dentition: The teeth are relatively heavier, longer, and more crowded. The index of the 

 superior molar-premolar series is 0.82± and of the inferior 0.80 to 0.84. 



Skeleton: Loomis (1933, pp. 727-728) has briefly characterized the skeleton as having seven 

 cervicals, thirteen dorsals, and seven lumbars. These are all lightly built, with high spines on the 

 posterior cervicals and anterior dorsals. The wide scapula has a curved anterior margin and a 

 straight posterior one, with a moderately high spine having a sinuous edge. The humerus, radius, 

 and ulna are long and slender, in fact unusually long for an oreodont. The carpals are similar to 

 those of the genoholotype, but the metacarpals are long, the whole ensemble making an unex- 

 pectedly long front limb. The pelvis is long and light. The femur, tibia, and fibula are shorter 

 than in M. chelonyx, as are also the metatarsals, thus showing, in contrast with the latter, longer 

 front limbs and shorter hind ones. The tarsus is essentially alike in both species. 



1924. 



Mesoreodon scotti Schlaikjer 1934 

 PI. XLIV, fig. 2 



Original Reference: Three new oreodonts. Proc. Boston Soc. Nat. Hist., XL, pp. 223-225. 



Type Locality: Muddy Creek, Wyoming. 



Geologic Horizon: Lower Miocene (lower Harrison). 



Type: Holotype, Cat. No. 17480 M.C.Z., nearly complete skeleton, collected by Professor F. B. Loomis, 



