378 



TITANOTHEEES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Dentition. — The statements made below refer to the 

 type specimen unless otherwise indicated. The su- 

 perior incisors in general are of the M. manteoceras 

 type but exhibit several differences, which, on the 

 whole, are progressive toward the Oligocene titano- 

 theres of the genus Brontops. The median pair of 

 superior incisors (i^) are distinctly the smallest of the 

 series and are assuming the degenerate conical form 

 seen in the Oligocene species of Brontops,'^'' a change 

 that is effected especially by the reduction of the 

 posterior cingulum and the rounding together of the 

 anterior and posterior faces, with the consequent 

 loss of prehensile or cropping function. The inferior 

 series are all still pointed, jDosteriorly cingulate, and 

 functionally of the cropping type; 12 is the largest of 

 the series and ia is the most reduced. The superior 

 incisors are nearly in a transverse line, but i^ is slightly 

 behind i^. The incisors are separated from the 



terior faces, and with low posterior U-shaped basal 

 cingula. 



The median incisors (ii) are somewhat compressed 

 laterally (height 15 mm., ap. 14) but exceed in size 

 the lateral pair. The second incisors (i2) are much 

 larger (height 18, ap. 18) and the lateral incisors (ia) 

 are the smallest (height 12, ap. 12, tr. 12) and the 

 simplest, although still incisiform. 



The canines are distinguished by robust, rounded 

 fangs, which diminish rapidly into forward-directed, 

 tapering, pointed crowns, again suggesting those of 

 M. manteoceras, especially by the posterior swelling at 

 the base and the sublanceolate, internally flattened 

 apex with faint anterior and posterior ridges. In the 

 superior canines the diameters at the base are trans- 

 verse 26 millimeters, anteroposterior 28; height 49. 

 The inferior canines exhibit much the same form (ap. 

 32 mm., tr. 28, height 52), the base of the crown sloping 



Figure 320. — Lower jaw of Protitanotherium emarginatum 



One-fourth natural size. Partial reconstruction of anterior part of jaw to ms from Princeton Mus. 11242 (type), Kennedys Hole, 8 miles 

 north of White River and 25 miles east of Oiu-ay Agency, Uinta Basin, Utah, Uinta C; ms and posterior part of jaw from Am. Mus. 

 2028, White River, Utah, Uinta C. 



canines at the sides by a narrow diastema (9 mm.) 

 and separated in the median line by a diastema (10 

 mm.) similar to that observed in Mesatirhinus mega- 

 rhinus. The lateral incisors (i^) are large pointed teeth 

 (height 21 mm. side, 17 front; ap. 17) with oblique 

 posterolateral basal cingula and rather sharp lateral 

 cutting edges. The second incisors (i^) are much 

 smaller (height 12 mm., ap. 14) with heavy posterior 

 basal cingula connected with the apex of the tooth 

 by a median ridge which divides the somewhat concave 

 posterior surface. The median incisors (i') are still 

 smaller (height 10 mm., ap. 11), with subspherical 

 crowns and posterior median ridges rising to unite 

 with the apex of the crown and obscure the cingulum 

 except on the posterolateral side. 



The transverse extent of the inferior incisors is 69 

 millimeters; they aU exhibit pointed crowns, with 

 uniformly convex anterior faces, more concave pos- 



" In the Oligocene genera probably the median pair of superior incisors (iO and 

 he lateral pair of inferior incisors (ij) had disappeared, leaving i>, i' and ii, ia (see 

 p. 448). 



backward into a deep, powerfully implanted fang, the 

 crown diminishing rapidly as it rises to a rounded, sub- 

 lanceolate apex. 



The premolar-molar series are separated by a short 

 diastema from the canines in both jaws (27 to 30 mm. 

 above, 23 below). A postcanine diastema of varying 

 length is seen in Telmatherium ultimum, T. altidens, 

 Manteoceras uintensis, Diplacodon elatus, and Protitano- 

 therium superhum, an indication that it is independ- 

 ently preserved in different phyla. Of the superior 

 teeth unfortunately p^ only is preserved. This is a 

 bifanged tooth measuring (ap. by tr.) 20 by 11 milli- 

 meters, with a simple protocone, a sessile or rudimen- 

 tary posterior heel, and a postero-internal cingulum 

 anci concavity. The alveolus of p" shows that it was 

 a broader and much more advanced tooth than that 

 in Manteoceras manteoceras. The inferior grinding 

 teeth measure about 294 millimeters in length, as 

 compared with 180 to 192 in M. manteoceras. 



In the type the lower premolar series measures 103 

 millimeters on the left side, in which pi is abnormal 



