TICHOLEPTUS 



193 



Ticholeptus petersoni Loomis 1923 

 Figs. 5, 141; PL XLVII, fig. 2 



Original Reference: Oreodons of the lower Harrison beds. Amer. Jour. Sci. (5), VI, pp. 225-227. 

 figs. 2-4. 



Type Locality : Directly back of Van Tassel, Wyoming. 



Geologic Horizon: Lower Miocene (lower Harrison). 



Types: Holotype, Cat. No. 22-656 A.M., skeleton, complete except for two dorsal vertebrx and hind leg. 

 Paratype, Cat. No. 22-652 A.M., specimen with "all four legs but a less perfect series of vertebras" than the HT. 

 Species named for the late Mr. O. A. Peterson, of the Carnegie Museum. 



Specific Characters: The skull is about the size of that of T. brachymelis but of somewhat 

 less depth facially. The superior contour is unusually flat. The zygomata are moderately light, 

 although the malar is heavy beneath the orbit. The squamosal part of the arch is not so widely 

 expanded as in T. brachymelis and does not rise so abruptly posteriorly. The facial vacuities are 



Fie. 141. — Ticholeftus fetersoni Loomis. Skull. HT. Cat. No. 22-656 A.M. 1/2 nat. size. (After Loomis, 1923.) 



large and triangular in shape, with the apex forward and the base abutting the lacrimal bone. The 

 maxillary and frontal are the other delimiting bones. The nasals are unusually short, with their 

 posterior terminations nearly on a line with the anterior points of the facial vacuities. These bones 

 are very gently convex in both directions. The lacrimal bone is nearly square in outline, extends 

 well onto the face, and wholly carries the deep lacrimal fossa. The frontals are rather large, trans- 

 versely convex, and extend forward of the lacrimal. The orbits are rather large and subround and 

 are vertically a trifle above center. They are definitely closed posteriorly by a postorbital bar which 

 is heavier than that in the genoholotype. The shallow temporal ridges unite in advance of a point 

 above the anterior edge of the glenoid surfaces to form a long sagittal crest. The supraoccipital 

 crest extends slightly beyond the occipital condyles, with but a moderate wing spread. The brain 

 case is low but has a considerable breadth laterally. The external auditory meatus extends directly 

 outward. The glenoid surface is very shallowly concave. The paroccipital process is fairly long and 

 tapers to a point. Index: 0.53a. 



Mandible: The posterior part is moderately wide and deep, with a nearly straight posterior 

 edge. The angle extends but slightly below the inferior margin of the horizontal ramus and in 

 general characters resembles that of T. zygomaticus. The angle of the symphysis is 45°. Vertically 

 the symphysis is slightly concave. The coronoid processes are low, the sigmoid notch is very 

 shallow, and the condyle is low and nearly flat. 



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



Dentition: Teeth slightly hypsodont. The molar-premolar index is 0.70. 



