478 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND- NEBRASKA 



lar, smoothly rounded crowns ; incisors smaller 

 tlian in Brontoiherium. Canines cf usually of 

 medium size, anterior face 40, 42, 48 milli- 

 meters, recurved, pointed crowns, often com- 

 pressed anteroposteriorly; canines 9 more 

 slender, shorter, and in section rounder. 

 Opposite molar-premolar series rectihnear to 

 arched. Upward flexure of premolars in side 

 view progressive and especially pronounced 

 in hyperbrachycephalic skulls; dental (pre- 

 molar-molar, basilar) index cf 46-50. 

 Premolars, tetartocone of p* typically re- 

 tarded, often a concave spur; tetartocones 

 of p^, p^ more progressive, but less so than 

 in Menodus; external cingulum typically less 

 prominent than in Menodus. Molars with 

 internal cingula less prominent than in 

 Menodus, crowns less hypsodont than in 

 Menodus. Skull cf brachycephalic to hyper- 



e'dc ha 



Figure 412. — Progressive broadening of 

 the nasals in the Bronto-ps phylum from 

 B. brachycephalus, with narrow nasals, 

 through B. dispar to B. robustus, with 

 broad nasals 



a, Brontops brachycephalus, Nat. Mus. 4947, Ghadron A 

 b, B. brachycephalus, Nat. Mus. 1214, Chadron, A; c, 

 B. brachycephalus, Nat. Mus. 1258, Chadron B; d 

 dispar, Nat. Mus. 4703, Chadron B; e, B. dispar, Nat, 

 Mus. 4696, Chadron C;/, B. robustus, Am. Mus. 1083, 

 Chadron C (?) 



brachycephalic, zygomatic index 73-91, skull 

 9 with narrow buccal arches. Nasals primi- 

 tively elongate, progressively shortened and 

 swelling at the extremities; nasal index 

 61-140. Horns cf primitively low, elongate, 

 ovoid, becoming cylindrical {B. dispar), club- 

 shaped {Brontops robustus) or with a small 

 secondary branch {Diplodonus) , roundly tri- 

 hedral (B. dispar) or broadly oval (Brontops 

 rohustus). Face progressively abbreviate. 



CONSPECTUS OF CHARACTERS OF SPECIES 



The salient features of the several species 

 are set forth in the following summary: 



Teleodus avus Marsh. The most ancient form re- 

 corded from the base of the lower beds. Readily dis- 

 tinguished by the three incisor teeth with rounded 

 crowns in the lower jaw, although the type is some- 

 what larger than B. brachycephalus. Phyletic position 

 somewhat doubtful. 



Figure 413. — Lower jaws of Teleodus primitivus, Brontops brachycephalus, 

 and Allops ualcottif 



A, Teleodus primitivus, Otta.wayias. (type); Cypress Hills, Saskatchewan; perhaps the smallest 

 and most prhnitive known jaw of an adult Oligocene titanothere, with horizontal ramus long and 

 moderately deep, chin gently convex, angle not projecting sharply backward, ascending ramus 

 relatively broad, coronoid of moderate height, three incisors, and a prominent postcanine 

 diastema. The external cingula of the cheek teeth are partly confluent with the ectolophs, 

 whereas in all other Menodontinae they are sharply defined. 



B, Brontops brachycephalus. Am. Mus. 1495; compared with the preceding has a horizontal ramus 

 very shallow anteriorly, angle projecting downward and backward, coronoid high, and molars 

 relatively larger. 



C, Allops walcottif, Nat. Mus. 4247; differs frona the typical Brontops in having sharply defined 

 external cingula and no diastema in front otpi (pi has dropped out). It differs from the known 

 Menodus in possessing incisors. 



All one-fifth natui'al size. 



