58 



THE MERYCOIDODONTID/F. 



Merycoidodon macrorhinus (Douglass) 1901(1903) 

 Fig. 24; PL II, figs. 7-8 



Original Reference: Fossil Mammalia of the White River beds of Montana. Trans. Amer. Philos. 

 Soc. (2), XX, pp. 243, 253, 264 (Oreodon robustum, preoccupied); New vertebrates from the Montana 

 Tertiary. Ann. Carnegie Mus., II, 1903, pp. 163-164, fig. 8 (Oreodon macrorhinus). 



Type Locality: Near the Missouri River, southeast of Helena and northeast of Toston, Montana. 



Geologic Horizon: Middle Oligocene (lower Brule). 



Type: Holotype, Cat. No. 767 CM., skull which lacks cover of brain case and zygomata and is otherwise 

 somewhat damaged. 



Specific Characters: The skull is about the size of that of M. culbertsonii, but the bones 

 are much heavier, and the face is a third higher above P 1 . The malar is heavy but not deep beneath 

 the orbit, while the origin of the zygoma is above P\ The nasal bones are posteriorly acute, are 

 very broad, nearly flat anteroposteriorly, and gently concave transversely. The -pars facialis of the 

 lacrimal bone is large, and the antorbital fossa is deep and is not confined to the lacrimal but invades 

 the maxillary. The wide frontals are unreduced and moderately flat and extend as a wedge in 

 advance of the lacrimal bones. The orbits appear to have been small and subround. The temporal 

 ridges, sagittal crest, and supraoccipital crest are missing. The brain case is wide, full, and rounded, 

 apparently without convexities. The palate is wide and gently vaulted, with the open V-shaped 



Fig. 24. — Merycoidodon macrorhinus (Douglass). Skull. HT. 



Douglass, 1903.) 



Cat. No. 767 CM. 1/2 nat. size. (After 



palatonarial border nearly on a line through the posterior lobes of the last molars. The basicranial 

 axis is steep. The glenoid articular surface is slightly convex. The postglenoid process is very 

 robust and is anteroposteriorly thick. The bulls are very small and are widely separated from the 

 basioccipital. The premaxillaries appear to have begun to coossify. Index: 0.62a. 



Foramina: The infraorbitals lie above the posterior portion of P 3 . The supraorbitals are 

 20 mm. apart, which is a greater distance than that in M . culbertsonii. The foramen ovale is unusu- 

 ally large, while the foramen rotundum is much smaller. The posterior palatine foramina are 

 opposite P 3 . 



Dentition: The canines are large. P 1 is small and narrow. The anterior three premolars 

 have large posterior basins and well-developed posterior crescents, with a reduction of the anterior 

 crescent. The anterior and posterior crests are strong, and the median crest is very weak or absent. 

 There are two tiny anterior pits separated by a weak anterointermediate crest. P 4 has a strong 

 internal cingulum and no anteroexternal pit. The molars are of the same pattern as those of M. cul- 

 bertsonii. The superior molar-premolar index is 0.90. 



