METOREODON 209 



The mandible is not of the same individual as the cotype skull. It belongs to a smaller animal, 

 but one larger than M. ? medius and nearer in size to M. profectus. The dentition shows it to be 

 more advanced than any previously described species in this genus. By analogy I judge it is of the 

 same stage of evolution as the cotype skull. The true canine is set at right angles to the tooth row, 

 the caniniform premolar is placed at an angle of 45° and P 2 at nearly 75° from the line of the teeth, 

 while P 3 is also obliquely placed to a higher degree than in any other known species of the genus. 

 In other words, the anterior three premolars are rotated inward to a much greater degree than those 

 of any known form of Metoreodon. The canines are of less depth than in the plesiotype of 

 M. profectus but are longer and narrower. P 3 is narrower for the same length, while P 4 is longer 

 for the same width. M x is shorter, M 2 is of about the same dimensions, while M 3 is shorter and 

 narrower. The lower molar-premolar index is 0.61 in this form and 0.62 in M. profectus. 



Discussion: These two cotypes were collected about five miles apart. The skull is heavy and 

 massive, besides being larger than the skull which belonged with the mandible. I believe this 

 belonged to a male and the mandible to a female. 



Both are much more advanced than any other Metoreodon, and it is my opinion that they 

 represent one of the culminations of this whole great group. 



The skeletons of three immature individuals in the American Museum of Natural History 

 apparently belong to this species. 



Metoreodon profectus Matthew and Cook 1909 

 Figs. 152-153; PI. XXX ; PI. XXXI, fig. 1 



Original Reference: A Pliocene fauna from western Nebraska. Bull. Ainer. Mus. Nat. Hist., XXVI, 

 Art. 27, pp. 394-395, fig. 15 (Merychyus [Metoreodon] frojectus). 



Type Localities: Twenty-three miles south of Agate, Sioux County (HT and PTs) ; Devil's Gulch 

 and Plum Creek, Brown County (PLTs), all in Nebraska. 



Geologic Horizon: Lower Pliocene (Snake Creek and Devil's Gulch). 



Types: Holotype, Cat. No. 14055 A.M.N.H., left inferior ramus, with dentition complete except for L and 

 P 4 . Paratypes, both in A.M.N.H., Cat. No. 14066, an upper jaw, and Cat. No. 14068, an individual M 3 . 

 Plesiotypes, both in Nebraska State Museum, Cat. No. 6-7-11-13, skull lacking the posterosuperior part of brain 

 case, and Cat. No. 5-7-11-13, lower jaw of young individual. 



Specific Characters: This species is about the size of Metoreodon ? medius, and of the larger 

 species of Merycoides. The skull is low and wide. The zygomata reach their greatest expansion at 

 the anterior part of the glenoid surfaces. The malar is decidedly robust and deep beneath the orbit, 

 flaring outward and downward. The postorbital process of the malar is very heavy. The squamosal 

 part of the zygoma is weak in comparison with the malar portion, and it rises in a gentle curve, with 

 its highest point in a plane above and just posterior to the postglenoid process. The malar extends to 

 the glenoid surface, and the squamosal extends to a point beneath the posterior part of the orbit. 

 The nasals are reduced in proportion to the size of the skull, but they have moved backward to pene- 

 trate wedge-like into the frontals to a point posterior to a line through the center of the orbits. 

 Anteriorly they terminate about over P 1 . The posterior part of the anterior narial opening is above 

 P 3 . The nasal bones rise anteriorly so that anteroposteriorly they are markedly concave, while 

 transversely they are gently convex forward and flat aft. The lacrimal bone has a large pars 

 facialis, bearing a large and deep pit. The frontals are wide, moderately flat, and unreduced. They 

 are somewhat depressed between the orbits and convex immediately above the latter, and they 

 extend in advance of the lacrimal bones. Their anterior termination is truncated. The orbits are 

 large, highly placed, and subovate in outline. The temporal ridges are slightly rugose and prob- 

 ably unite just back of the postorbital constriction. The brain case is wide and apparently well 

 rounded. The palate is wide and vaulted to a slight degree. The palatonarial border is posterior 



