EVOLUTION OP THE SKULL AND TEETH OF EOCENE TITANOTHERES 



351 



including as progressive features (1) the prominence 

 and the backward extension of the paraconid into a 

 parastylid; (2) the variable but distinct metastylid 

 ridge; (3) the external position of the hypoconulid 

 on 1X1} and the prominent internal ridge on it, which 

 gives it a concave form internally; (4) the external 

 cingulum slightly more progressive than in M. 

 manteoceras and dipping somewhat into the valleys 

 but not so deeply as in D. hyognathus. 



Lower jaw of T. ultimum. — The jaw of this specimen 

 is represented by that of the type (Am. Mus. 2060). 

 The type jaw retains the characters of T. cultridens 

 in the rather slender recurved coronoid process but 

 departs from them by its rapidly increasing depth 

 posteriorly — in fact, the whole j aw is relatively deeper 

 than in the ancestral species. The distance from 

 the condyle to the incisive border is estimated at 

 435 millimeters in the type. The chin is strongly 

 compressed laterally (54 mm.), and behind it the jaw 

 gradually broadens and deepens, the lower border 

 being more nearly straight than in M. manteoceras 

 and terminating in the slightly depressed and back- 

 wardly produced angle; the condyle exhibits two 

 marked peculiarities: the outer half of the rotular 

 facet extends broadly forward, whereas the inner half 

 has a straight anterior border and unites posteriorly 

 by a much broader union than in M. manteoceras 

 with the broad facet for the postglenoid process. 

 The coronoid process, perfect in the type, is rather 

 narrow and uniformly recurved. The striking resem- 

 blance to T. cultridens observed in the dentition of 

 this species is therefore not seen in the jaws, which are 

 relatively shorter, more massive, and deeper posteriorly 

 (below ms) than in T. cultridens, all of which are pro- 

 gressive characters. 



A second jaw (Am. Mus. 2033) was at first doubt- 

 fully referred to the same species. In this jaw the 

 second premolar is spaced as in the type. In other 

 features, as in ps, in the coronoid process, and in the 

 proportions of ma, this jaw resembles those of members 

 of the Manteoceras phylum, to which this one is now 

 provisionally referred. (See Manteoceras uintensis, 

 below.) 



A skull in the Carnegie Museum (No. 2339) differs 

 from the type and paratype in having a longer tooth 

 row but shows generic agreemeiit with T. ultimum 

 in the general form of the skull, especially of the 

 zygomata, occiput, and nasals. 



Telmatherium altidens Osborn 



Plate LXV; text figures 127, 299, 300 

 [For original description and type references see p. 184] 



Type locality and geologic Tiorizon. — Uinta Basin, 

 Utah; Uinta formation, Diplacodon-ProtitanotJierium- 

 EpiMppus zone (Uinta C). 



Specific characters. — Pj-ms, 313 millimeters; a wide 

 diastema (55 mm., estimated) behind the inferior 



canines; canines in males elevated (76 mm., estimated) 

 and pointed; pi_2 laterally compressed, nonmolari- 

 form; p3_4 submolariform. Subdolichocephalic, upper 

 postcanine diastema elongate. 



Materials. — As described in Chapter III, this animal 

 is known only from a single lower jaw (Am. Mus. 2025) 

 with no parts of the skull or skeleton associated. 



Comparison. — The reference of this specimen to the 

 genus Telmatherium depends chiefly upon (1) the large 

 size and vertical elongation of the canines, as in 

 T. validum; (2) the very large size of the lower incisors; 

 (3) the exceptional elongation of the lower postcanine 

 diastema, which is incipient in T. ultimum but was 

 evidently carried to a much greater extreme in T. alti- 

 dens; (4) p2 much less molariform than in Protitano- 

 therium and hence more like the simple, laterally com- 

 pressed p2 of T. ultimum; (5) the very large size of the 

 lower molars (mi_3), the form of which indicates large, 

 broad upper molars, as in T. ultimum. 



The skull when discovered may well prove that this 

 animal represents a well-marked new generic stage. 

 On the other hand, the very large incisors and lofty 

 canines, the pronounced diastema, the characters of 

 Pi, p2, and the large, broad molars, as noted above, 

 appear to indicate generic Idnship with T. ultimum. 



Chief characters. — The exceptionally long mandibu- 

 lar symphysis and wide postcanine diastema, as fore- 

 shadowed in T. ultimum, distinguish this titanothere 

 as possessing a relatively elongated facial region. 

 This character, as well as the long, relatively shallow 

 jaws, the elongation of ms, and the wide space behind 

 ma, is evidence that the skull as a whole was sub- 

 dolichocephalic, although far less so than that of 

 Dolichorhinus. In common with T. ultimum, "T. inci- 

 sivum," Protitanotherium, and all other upper Eocene 

 and Oligocene forms, T. altidens had undergone a dif- 

 ferential elongation of the middle part of the skull, 

 which allowed the molars to become extremely large, 

 both absolutely and as compared with the premolars. 

 The elevated, piercing canines are also exceptional 

 among titanotheres; they exceed those of the ances- 

 tral species. Thus the animal is very readily distin- 

 guished from any of the known species of the contem- 

 porary Diplacodon and Protitanotherium. A fourth 

 feature is the simple, nonprogressive, elevated, and 

 somewhat laterally compressed form of p2, which is 

 decidedly more primitive than the corresponding tooth 

 in Protitanotherium. 



The cracked and much weathered teeth of this male 

 individual (Am. Mus. 2025) fortunately include the 

 median incisors (ij) of the opposite sides, the left 

 canine, and the entire grinding series of the right side 

 in sufficient preservation to define the species sharply. 

 In detail the median incisors are much larger, with 

 more pointed tips than those of Protitanotherium 

 emarginatum, measuring 19 millimeters on the anterior 

 face, 20 anteroposteriorly, and 15 transversely. These 



