METOREODON 



203 



Metoreodon californicus (Merriam) 1917 

 Figs. 146-147 



Original Reference: Relationships of Pliocene mammalian faunas from the Pacific Coast and Great 

 Basin provinces of North America. Bull. Dept. Geol., Univ. Calif., X, p. 431 (Merycochcerus [Pronomo- 

 therium] californicus, n. sp. — name only, in Ricardo faunal list); Tertiary mammalian faunas of the Mohave 

 Desert. Ibid., XI, pp. 575-578, figs. 211-215, 1919 (first description). 



Type Locality: Univ. Calif. Coll. Loc. No. 1755. On the west wall of the first canyon west of Red 

 Rock Canyon, west-northwest of Ricardo Post Office, Mohave Desert, California. 



Geologic Horizon: Lower Pliocene (Ricardo). Fine-grained buff micaceous sandstone. 



Types: Holotype, Cat. No. 21351 U.C.M., fragmentary skull with molar dentition. Paratypes, Cat. No. 

 23128 U.C.M., fragment of right upper jaw with last three premolars; Cat. No. 21353 U.C.M., skull frag- 

 ment with well-worn molars; and Cat. No. 21567 U.C.M., symphysial area of mandibles. 



Specific Characters: The skull, if complete, should be about the size of that of M. major, 

 judging by the size of the comparable teeth in both species. Unfortunately the holotype skull is 

 considerably crushed and the anterior part is missing. The face was depressed back of the anterior 

 nares. The zygomatic arch is incomplete, but it was short anteroposteriorly. The malar is consid- 



Fic. 146. — Metoreodon californicus (Merriam). Inferior view of skull. HT. 



(Redrawn from Merriam, 1919.) 



Cat. No. 21351 U.C.M. 1/4 nat. size. 



erably expanded and deep beneath the orbit. The maxillaries and premaxillaries slope backward at a 

 rather low angle, indicating the recession of the anterior narial opening. The orbits are small. The 

 sagittal crest is low, and the supraoccipital crest strongly overhangs the occipital condyles. The brain 

 case is laterally expanded and well rounded, so that the occipital region is extremely wide. The 

 U-shaped palatonarial border lies well back of the posterior of M 3 , and the palate is wide. The basi- 

 cranial axis is moderately shallow. The wide mastoid plates merge into the heavy, robust paroccipital 

 processes, which are relatively long. Index: 0.70a. 



Dentition: The molars are large, and their combined length is unusually great, with a molar- 

 premolar index of 0.61. In both M. projectus and M. novomexicanus it is 0.66. The protocone is 

 larger than the hypocone on each molar, and the styles are well developed, progressing in size from 

 molars 1 to 3. 



The premolars are typical of Metoreodon but have not advanced so far as those of M. novo- 

 mexicanus, though they seem to be at about the stage of M. profectus. The anterointernal tubercle 



