MERYCHYUS 217 



anterior to a plane through the posterior of the canines, and widest at contact with maxillaries ; 

 malar medium and zygomatic arches light; orbits large; occiput moderately broad; bulla; large; 

 frontals unreduced; dentition subhypsodont to hypsodont;. anterior upper molars reduced ante- 

 riorly, appearing to slant backward; molars increasing very gradually in length in earlier forms and 

 more rapidly in later ones; M 1 and M 2 tending to be nearer in length than M 2 and M 3 ; lower 

 premolars less crowded in earlier than in later species; P 4 well developed posteriorly in all species; 

 lower molars increasing rapidly in length posteriorly, so that length of M, is half that of M 3 ; neck 

 short; legs and feet slender, light, and of moderate length ; four toes on all feet; body of medium 

 length; and ribs light. 



Etymology: Merychyus (ruminant + pig). 



Species: 



M. arenarum Cope 1 884. 



M. arenarum leptorhynchus Cope 1 884. 



M. arenarum minimus Peterson 1906. 



M. curtus Loomis 1 924. 



M. delicatus Loomis 1 924. 



M. elegans Leidy 1 858. Genotype. 



M. elegans paniensis Loomis 1924. 



M. euryops (Cope), nomen nudum. 



M. h arris onensis Peterson 1906. 



M. pariogonus Cope 1 884. 



M. siouxensis Loomis 1924. 



Merychyus arenarum Cope 1884 

 Fig. 160; PI. XXXII, figs. 1-3 



Original Reference: Synopsis of the species of Oreodontidae. Proc. Amer. Philos. Soc, XXI, pp. 540- 

 542, pi. XXVII. 



Type Locality: East of Laramie Peak, Wyoming. 



Geologic Horizon: Lower Miocene (upper Harrison). 



Type: Holotype, Cat. No. 8146 A.M.N.H., skull, lacking anterior part of muzzle; mandible, nearly 

 complete except for coronoid process; fore and hind feet; and other limb bones. Collected by J. C. Isaac. 



Specific Characters: The skull is small, a trifle larger than M. siouxensis, moderately wide, 

 with very gently arched superior contour, and moderately low. The malar is deep beneath the arch, 

 but the zygomatic process of the squamosal is slender, nearly straight except for an abrupt rise at the 

 posterior angle, and with the maximum expansion occurring just in advance of the glenoid surface. 

 There is a small facial vacuity bounded by the lacrimal, maxillary, and frontal. It is subtriangular 

 in outline, with the base above. The nasals are not reduced, are of fairly uniform width, and are 

 posteriorly obtuse. The lacrimal is large and forms part of the face, in which lies a large but shallow 

 lacrimal fossa. The frontals are wide and transversely convex. The orbits have the longer diameter 

 anteroposteriorly and are not elevated. They look mainly sidewise. The temporal ridges are very 

 low, uniting above the glenoid surfaces to form a short, low sagittal crest. The supraoccipital crest 

 is low, overhanging the occipital condyles, and the wings are moderately spread apart. The brain 

 case is large but low. The external auditory meatus opens directly outward, with a slight upward 

 direction. The palate is wide and nearly flat, with the palatonarial border a little posterior to the last 

 molar. The basicranial axis is not steep. The glenoid surface is nearly flat, and the postglenoid 

 process is small and anteroposteriorly narrow. The paroccipital processes are small and triangular in 

 cross section. Index: 0.63. 



