TICHOLEPTUS 191 



the occipital condyles and the wings were not very widespread. The brain case is low and short but 

 rather wide. The palate is narrow, and the U-shaped palatonarial border is opposite the posterior 

 edge of M 3 . The basicranial axis is moderately inclined. The glenoid surface is nearly flat. The 

 postglenoid process was small and stocky, bounding only the inner half of the glenoid surface. The 

 paroccipital processes are very broad transversely and thin anteroposteriorly, with a convex surface 

 aft and a concave one forward. The bullae are missing but apparently were of relatively enormous 

 size. Index: 0.69a. 



Mandible: The ascending ramus is rather deep but only moderately wide, with the posterior 

 border apparently less vertical than in T. zygomaticus. However, as most of the border is missing, 

 we cannot be certain of this. The condyle is small, with the sigmoid notch wide open and the 

 coronoid process short, slender, and very thin transversely. The masseteric fossa is small and 

 narrow anteroposteriorly. The angle of the symphysis is 47° and the chin is very gently concave 

 vertically. There is a small tubercle at the base of the symphysis. The inferior border of the 

 horizontal ramus is nearly straight, and the depth is moderate. 



Foramina: The infraorbitals lie above the anterior part of P 4 . The supraorbitals are small 

 and apparently double, with the outer one 13.5 mm. from the mid-line. The basicranial foramina, 

 as in the later oreodonts, have no foramen rotundum. The posterior palatines are opposite P 4 . 



Dentition: The teeth, especially the molars, are hypsodont, as we should expect in the upper 

 Miocene. In all species of this genus the molar series is longer than the premolar, but in T. brevicefs 

 this feature is carried farther than in any other except T. fetersoni which has the same molar-pre- 

 molar index, 0.70. The combined length of M 2 and M 3 is about a quarter more than the total 

 premolar length. In T. brachymelis and T. zygomaticus, M 2 plus M 3 is slightly less than the 

 length of the premolar series, but in T. fetersoni M 2 plus M 3 is slightly more than the combined 

 premolar length. P 1 , P 2 , and P 3 overlap, and the diastema between C and P 1 is unusually small. 

 The tooth patterns are typical of the genus. The external styles on the molars are decidedly promi- 

 nent, as in T. zygomaticus. The inferior teeth in advance of the molars are all crowded. The 

 incisors are small; the C is leaf-shaped and about twice the size of I 3 . The premolars all overlap. 

 The last lobe of M 3 is nearly in line with the other lobes and is not turned inward, as it is in 

 T. hy-psodus, for example. 



Skeleton: The limbs and feet are moderately short, about the length of those in Merycoidodon 

 culbertsonii. 



Discussion: This skull is much more brachycephalic than that of any of the other species so far 

 known. The index is about 0.69. The zygomatic arch is relatively heavier, and so are the molars in 

 relation to the premolars. The nasals are shortened, and the premaxillaries are coossified. There 

 are several characters distinguishing this species which cause it to deviate from the Tichole-ptus norm. 

 Whether they are due to age, sex, or evolution (this being an upper Miocene form), we cannot 

 know definitely until more material of this species is brought to light. I judge it to be an advanced 

 stage of the genus. 



Ticholeptus hypsodus Loomis 1924 

 Fig. 140 



Original Reference: Miocene oreodonts in the American Museum. Bull. Amer. Mus. Nat. Hist., LI, 

 Art. I, pp. 35-36, fig. 25. 



Type Locality: Twenty-three miles south of Agate, Nebraska. 



Geologic Horizon: Probably upper Miocene (lower Snake Creek) but possibly lower Pliocene (upper 

 Snake Creek). 



Type: Holotype, Cat. No. 14057 A.M.N.H., fragmentary right lower jaw, with molar series and P 3 . 4 

 complete and alveoli of Pi and P 2 . 



