354 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



canine diastema is reduced or absent; (3) the superior 

 premolars p^ p\ p* are more progressive than in T. 

 ultimum, having very heavy internal cingula and pro- 

 nounced external cingula; (4) the basicranial region 

 differs in many details. 



The type skull of the species (Carnegie Mus. 2398) is 

 vertically crushed, a condition that led to some errors 

 in the original description of the species which a second 

 skull in the Field Museum (No. 12168) enabled Greg- 

 ory to correct and to reach the following conclusion 

 as to the affinities of this animal: 



Relation to Telmafherium. — StTienodedes is sharply 

 separated from the Dolichorhininae and at the same 

 time allied with Telmatherium by the following char- 

 acters: (1) General contour of the skull in basal view, 

 wholly unlike MetarMnus and resembling Manteo- 

 ceras or Telmatherium; (2) complete absence of infra- 

 orbital protuberance, the infraorbital portion of the 

 malar more like that of either Manteoceras or Telma- 

 tJierium; (3) midportion of malar with deep vertical 

 flange as in Telmatherium (contrast Metarhinus) ; 

 (4) incisors and canines readily derivable from the 

 Telmatherium type (compare figures of side view, 

 crown view; compare premaxillaries); (5) dentition 

 extremely macrodont (microdont in Metarhinus, 

 TQ.B.CYoAontm Telmatherium); (6) premolars more ad- 

 vanced than in T. ultimum but derivable from the 

 Telmatherium type (cf . T. validum) by enlargement of 

 internal cingulum, filling out the internal contour of 

 p^; (7) referred lower jaw (Field Mus. 12168) de- 

 cidedly nearer to Telmatherium ultimum than to 

 Metarhinus, macrodont, especially molars, ramus mas- 

 sive and deep; (8) basis cranii with postglenoid, post- 

 tympanic, meatus, and basioccipital nearer the 

 subbrachy-mesaticephalic type of Telmatherium than 

 to the subdolichocephalic type of Metarhinus. 



Through parallel evolution there are some marked 

 resemblances to the Dolichorhininae, as follows: (1) 

 Premolars (p^~*) with very heavy internal cingula and 

 crowns well filled out on the inner side; (2) incisors 

 cupped by upgrowths of heavy cingulum; (3) subhyp- 

 sodonli or elongate character of the molars of the 

 type specimen. 



Effects of crushing. — To the vertical crushing of the 

 type skull is possibly due the wide displacement of 

 the lacrimal bones on both sides of the face, result- 

 ing in the false appearance of "lacrimal pits." To the 

 crushing is also due the union of the postglenoid and 

 post-tympanic processes, the depression of the occiput, 

 and the abbreviation of the nasals. 



Sthenodectes incisivus (Douglass) 



Plates LXV, LXVI; text figures 129, 130, 301 



[For original description and type references see p. 185) 



Type locality and geologic horizon. — About 3 miles 

 northeast of well 2, Uinta Basin, Utah; upper levels of 

 Eohasileus-Dolichorhinus zone (Uinta B 2). 



Specific characters. — Skull, length 488 millimeters, 

 zygomatic breadth 305 millimeters, cephalic index 62. 

 Dentition, p^-m^ 207 millimeters; m^-m^ 125; p^ 

 large (ap. 19 mm., tr. 22), very progressive, with 

 advanced tritocone and complete internal cingulum, 

 deuterocones of p^~* relatively elevated, internal 

 cingula heavy, complete, m' (ap. by tr.) 42 by 45 

 millimeters with reduced posterior metacone crescent. 



Materials. — Besides the type skull in the Carnegie 

 Museum (No. 2398), on which the above specific 

 characters are based, there is a well-preserved skull in 

 the Field Museum (No. 12168), also a pair of lower 

 jaws (Field Mus. 12166). According to Riggs (1912.1, 

 p. 38) all three specimens are from the same locality 

 and belong to the same species. The skull and lower 

 jaws in the Field Museum were discovered by Abbott 

 in the lenticular sandstones near well 2 at the foot of 

 Coyote Basin. The skull, Field Mus. 12168 (PL 

 LXVI), is shorter (460-300 mm., cephalic index 

 65) than in the type of S. incisivus but has the 

 broad-crowned molars and massive incisors of that 

 species. At approximately the same geologic level but 

 half a mile distant was found the lower jaw (Field Mus. 

 12166) referred to this species (PL LXVI), which 

 belongs to an older individual, as is evident from the 

 worn molars and incisors. It is described below. 



This short-headed, massive-jawed titano there ex- 

 hibits a remarkable combination of characters. It 

 exceeds all other known titanotheres in the size of the 

 incisor teeth, which are correlated with the massive 

 jaws and the relative abbreviation of the skull, the 

 general proportions of which suggest those of Manteo- 

 ceras. The abbreviation of the facial region consti- 

 tutes a differentiation directly the opposite of that 

 which was occurring in the line which gave rise to 

 Telmatherium altidens in Uinta C, in which the face, 

 judging by the wide postcanine diastema, was elon- 

 gated. The indices are significant. 



Indices of Sthenodectes incisivus 



Cephalic index 



Faoiocephalic index.. 

 Molar-cephalic index 



Carnegie 



Mus. 2398 



(type) 



Field Mus. 



12168 

 (referred) 



65 

 44 

 28 



The grinding teeth are also proportionally very 

 large. The skull is at once separable from that of 

 Mesatirhinus and Dolichorhinus by the short basi- 

 cranial region and the stout, wide, spreading zygo- 

 mata, as well as by the heavy, short premaxillae and 

 the absence of a rounded infraorbital protuberance, or 

 shoulder. It also differs from any of these genera in 

 the proportions of the molar teeth, m^ and m^ being 

 wider, or more brachycephalic in type. It parallels 

 the true" Dolichorhininae, however, in the advanced 



