482 



TITANOTHERES OF ANCIENT "WYOMING, DAKOTA, AND NEBRASKA 



which in turn are a trifle larger than the external 

 pair. The incisors of Teleodus avus thus differ widely 

 from those of Protitanotherium emarginatum, since 

 they are round topped and small instead of being 

 flat topped and large. The canines are of medium 

 size, rounded in basal section, with faint posterior 

 cingula. The presence of only three premolars is also 

 noteworthy. There is no alveolus for pi. P2 is 

 separated by a narrow diastema from the canine. 

 The combined measurement of the three premolars 

 (106 mm.) is only 5 millimeters greater than that of 

 the posterior molar, which shows in a marked way the 

 inferiority of the premolar to the molar series. 



The jaw represents an individual slightly smaller 

 than the paratype of Menodus proutii Leidy and larger 

 than the jaws attributed to Brontops hrachycepJialus. 

 The canines show that this specimen was a male, and 

 the advanced wear of the molar teeth indicates that 

 the animal was fully adult. The external cingulum is 

 deficient opposite the widest part of the molar crowns, 

 whereas in Menodus and Brontops the cingulum tends 

 to surround the molars completely; in fact, through- 

 out the series the external cingulum is not very promi- 

 nent. The internal crest of the hypoconulid of ma 

 is moderately developed and crenulate. 



Taken together the characters of the canines, of 

 the incisors, and of the grinding teeth suggest affinity 

 to Brontops, and for the present we may regard the 

 genus Teleodus as of subgeneric rank. 



Teleodus primitirus (Lambe) 



Text figures 204, 413, A 

 (For origina] description and type references see p. 235) 



Type locality and geologic horizon. — Cypress Hills, 

 Saskatchewan; lower TitanotJierium zone. 



Specific cJiaracters. — ly, P^. Second lower incisor 

 the largest, median lower incisor the smallest, crowns 

 rounded. Premolars, 103 miUimeters (estimated); 

 molars 183 (estimated). Lambe writes: 



In the Cypress Hills specimen the crowns of the incisors are 

 of a depressed spherical shape, with a tendency to come to a 

 rounded central point above. The second incisor is the largest, 

 and the first is slightly smaller than the third, which is the 

 most upright. The first is more procumbent than the second. 

 Between the inner pair is a very decided interval, leaving a 

 space of 6.5 millimeters between the crowns of the two teeth. 

 The crowns of the canines are broken off, * * * and the 

 right first premolar is lost from its alveolus. [Lambe, 1908.1, 

 pp. 49, 50.] 



This apparently valid type represents the smallest 

 and most primitive Oligocene titanothere known at 

 the present time (1914). It is from the Cypress 

 Hills of Saskatchewan. It differs from T. avus in its 

 inferior size, in the presence of four lower premolars 

 and in the proportions of the incisor teeth, in which 

 is is smaller than ii. The rounded form of the 

 crowns of these incisors relates them to those of B. 

 irachycephalus. Another Brontops affinity is seen in 



the presence of an external cingulum on the grinding 

 teeth. Lambe's detailed comparison with " Menodus" 

 angustigenis Cope is as follows (op. cit., p. 50): 



Compared with Megacerops angustigenis (Cope) * * * 

 M. ■primiiivus differs in the following respects: There are six 

 incisors instead of four, and the breadth of the jaw between the 

 canines, which are of smaller diameter, is relatively greater; 

 the diastema between the canine and the first premolar is twice 

 as long; the symphysis is of greater length, reaching back to a 

 point almost in line with the posterior edge of the fourth 

 premolar (in angustigenis in line with the anterior root of the 

 corresponding tooth) ; the exterior cingula are much less de- 

 veloped; the coronoid process is shorter. In both species the 

 premolars have reached about the same stage of development 

 toward the molar pattern, and the molars have very much the 

 same proportions. In angustigenis the internal cingula are 

 partially developed. In primitivus the mandible is shorter, 

 proportionately deeper, and not so thick in the neighborhood 

 of the alveolar border posteriorly. 



Brontops Marsh 



("Megacerops phylum," Osborn, 1902) 



Plates XVIII, XX, XXI, XXIII, XXIV, XXXIII-XXXVI, 

 XLIII, XLVII, LXXXII-CIII, CLIII, CLX, CXCV- 

 CCXXIX; text figures 24, 28, 176, 179, 180, 195, 374, 375, 

 384-387, 389, 391, 393, 394, 396, 398-400, 406, 408-425, 

 482, 483, 510, 606-611, 616, 618, 622-024, 626, 628, 630, 635, 

 636, 639, 640, 650, 651, 653-655, 657-660, 665, 669, 673, 685, 

 686, 693, 699, 708, 712, 719, 727, 744, 746 



[For original description and type references see p. 222. For skeletal characters 

 see pp. 674-6761 



Geologic horizon. — From lower to upper TitanotJie- 

 rium zones. 



Generic characters. — Upper and lower incisors 2-1. 

 Canines pointed, becoming obtuse. Premolars cin- 

 gulate; tetartocones retarded. Horns of an elongate 

 to transverse oval section, shifting forward. Skulls 

 progressively brachycephalic. 



Incisors. — The Brontops phylum exhibits an assem- 

 blage of characters that sharply mark it off from the 

 main phyla of Brontotherium and Megacerops, as 

 follows : In young animals there are two upper incisor 

 teeth on each side (i^, i^), which in some specimens 

 tend to be reduced in old age to one on each side (i^) 

 by the loss of the median incisor; thus the incisive 

 formula, ffx) clearly distinguishes these animals from 

 Menodus and Megacerops, in both of which the in- 

 cisors are vestigial, the formula being f^. In Bronto- 

 therium the formula is the same (fEy,) but both upper 

 incisors, in the males at least, are strongly persistent. 



Canines. — In the early stages of Brontops the canines 

 are less elongate and less pointed than in Menodus, 

 less robust and obtuse than in Brontotherium, but 

 somewhat larger than in the feebly armed Megacerops; 

 they are generally of a graceful, recurved form. 



Premolars. — As noted above, the premolar grinding 

 teeth are decidedly retarded in complication — that is, 

 in the assumption of tetartocones and a molar pattern. 

 Thus the premolars of these animals from levels B 

 and A can readily be distinguished from those of 

 Menodus, which are advanced or progressive in com- 



