2Q2 THE MERYCOIDODONTIML 



Genus METOREODON Matthew and Cook 1909 



Table 1 1 



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

 Art. 27, pp. 391-392 {Merychyus, subgen. Metoreodon subgen. nov.). 

 Genotype: Metoreodon relictus Matthew and Cook. 

 Genoholotype: Cat. No. 14U56 A.M.N.H., right mandible, with incisors, canine, M 2 , and ascending 



ramus missing. 



Distinguishing Characters: Size range from about that of Merycoidodon culbertsonii to that 

 of a large Merycochcerus ; skull brachycephalic; nasal bones reduced anteriorly; premaxillaries 

 moderately large, coossified, and extending some distance upward and backward but probably not 

 quite reaching nasal bones; face (including orbits) considerably more than half _ of total length of 

 skull and depressed between orbits and toward back of nasal bones; frontals wide, flat, and unre- 

 duced; orbits small to medium in size and moderately high; malar very deep and posterior part of 

 zygomatic arch moderately light in comparison with anterior part; occiput broad and brain case 

 wide and low; facial vacuities large; infraorbital fossa rather large and moderately deep; bulls 

 medium to large; mandible rather slender for size of animal, with symphysis coossified; infra- 

 orbital foramen above posterior part of P 4 to anterior of M 1 . 



Dentition: Strongly hypsodont. Superior anterior premolars sloping backward, as in Mery- 

 chyus, and quadratic, with P 1 " 2 longer than wide and with anterointernal tubercle and cingulum 

 well developed; superior molars showing marked increase in length between P 4 and M 1 , and proto- 

 cone larger than hypocone; canine reduced; incisors pointed, although I 3 is somewhat spatulate. 

 Inferior Pi premolariform and generally reduced; cusp-like pillar on P 4 enlarged almost to bound 

 anterior basin, while posterior part of tooth is small to medium sized; anterior crescent of P 3 nearly 

 bounding anterior basin, and posterior basin divided more or less completely by posterior inter- 

 mediate crest nearly parallel to median crest; Mi and M 2 nearer in length than M 2 and M 3 ; heel 

 of M 3 nearly in line with tooth row and showing tendency to be bifid. Index of lower molar- 

 premolar series 0.63 to 0.69. 



Discussion: The structure of the premolar teeth in this genus is very distinctive. The reduc- 

 tion of the canine is more pronounced than in any other genus of the family, although this character 

 appears sporadically in certain merychyid forms from the lower Miocene formations. 



The structure of the face indicates that the genus had a more or less flexible snout, but hardly a 

 proboscis like Pronomotherium, since the recession of the anterior nares has not been developed to 

 such an extent as in that genus, nor as in Merycochcerus. 



There is a progressive development in size and in premolar complication of crown structure in 

 the species now assigned to this genus. M. relictus is probably the most primitive, while M. cali- 

 fornicus may well be the largest form, or at least it shares this honor with M. novomexicanus, which 

 has the generic premolar characters developed to a greater degree than any of the other forms. 



Etymology: Metoreodon (after or later + Oreodon). 



Species: 



M. calif or nicus (Merriam) 1917. 



M. com-pressidens (Douglass) 1901. 



M. major (Leidy) 1858. 



M. medius (Leidy) 1858. 



M. novomexicanus (Frick) 1929. 



M. profectus Matthew and Cook 1909. 



M. cf. M. profectus Matthew and Cook 1909. 



M. relictus Matthew and Cook 1909. Genotype. 



