224 THE MERYCOIDODONTID/E 



cave, while the U-shaped palatonarial border is definitely posterior to M' ! . The basicranial axis is 

 not steep. The glenoid surface is gently convex anteroposteriorly, and the glenoid process is small, 

 with the inner side almost touching the relatively enormous bullae. These bulla; give the appearance 

 of foreshortening to the basicranial region. The paroccipital processes are short and more plate-like 

 than usual. Index: 0.62. 



Mandible: The chin is steeper than in some of these species. It forms an angle of 50° with the 

 tooth row, and its face is very gently concave vertically. The mental tubercle is more prominent, 

 descending below the forward inferior line of the ramus. The coronoid process is small, the sigmoid 

 notch is shallow but well marked, and the gently convex condyle is placed forward of the posterior 

 line of the ascending ramus. 



Foramina: The infraorbitals are above the interval between P 3 and P 4 . The supraorbitals are 

 fairly close to the mid-line, with shallow grooves extending medially forward. 



Dentition: The molar teeth are nearly square in outline, and the premolars are wide trans- 

 versely and tend to shorten anteroposteriorly. The first three upper premolars are anteriorly abbre- 

 viated, with several small stria; extending forward from the main cusp. The posterior crescent is 

 normal but apparently does not unite with the median crest. P 4 looks as if its inner portion had been 

 twisted forward and is not symmetrical, as it is in M. elegans. It has a tiny pit in the anteroexternal 

 corner. 



Skeleton: Loomis has described the skeleton of M. curtus in comparison with M. a. minimus 

 Peterson. Both are nearly of a size in regard to the skulls, but the skeleton of the former is some- 

 what longer and much taller. 



The skull has a large antorbital fossa and a small facial vacuity. The reverse is true for 

 Peterson's species. 



The vertebral column closely resembles that of M. a. minimus. 



Loomis (1933, pp. 724-725) wrote of this species as follows: 



In the front limb the scapula of M. curtus, although equally wide, is less angular, and the spine has a less 

 distinct metacromion process than that in M. minimus. The humerus has the proportions characteristic of the 

 genus, but this species is peculiar in having an epicondylar foramen of fair size. The radius is markedly curved, as 

 in Leftauchenia. The ulna is stout, its square-topped olecranon process being curved toward the front, giving the 

 bone a peculiar form not seen in M. minimus but characteristic of Leftauchenia. The sigmoid notch is deep and 

 has the appearance of a notch cut into the side of a straight bone, again resembling Leftauchenia. The carpus 

 is of the character normal for an oreodont but has the individual bones elongated vertically. In M. curtus the 

 lunar does not crowd down between the unciform and magnum as far as it does in M. minimus. The metacarpals 

 are moderately elongated, and Digit I is reduced to a tiny vestige, seen only in an unusually well preserved foot. 

 It is in this respect that Leftauchenia differs markedly from Merychyus, the former having Digit I complete to 

 the last phalanx, the latter having but the tiniest vestige of the digit, with the tetradactyl foot elongated throughout. 



The pelvis is similar to that of M. minimus, except that the tuberosities are less pronounced. The femur is 

 relatively short and stout, with a normal greater trochanter and a weak lesser trochanter. The tibia is also rela- 

 tively stout, but longer in proportion than is the femur. The fibula is well developed throughout its length, and 

 heavier than that of M. mmirnus. The tarsus is similar to that of M. minimus and not so slender as that of 

 M. siouxensis. It differs from the tarsus of both species in having the middle and external cuneiform bones fused. 

 Digit I is represented by a tiny scale of bone immediately behind the contact between Digit II and the middle 

 cuneiform. Overlapping the contact between Digit V and the cuboid there is a small scalelike bone which the 

 writer has never before seen in an oreodont. . . . The metatarsals are developed much as in M. minimus and 

 are of about the same size. 



Discussion: Loomis feels that this skeleton confirms his opinion that Merychyus and 

 Leftauchenia are close of kin and that, to use his own words again, they "represent a group which 

 early separated from the phylum that contains Eforeodon, and then divided into two lines, the 

 one slender and long-limbed — Merychyus — the other slender but short-legged — Leftauchenia, 

 Cyclofidius, etc." 



