380 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



P. superhum is distinctly of the Manteoceras and 

 Protitanoiherium phylum. It is, however, more pro- 

 gressive toward the Brontops stage in that it is larger, 

 that its canines are extremely robust, and that p2_4 are 

 a little longer but mi_3much longer than in P. emargi- 

 natum. We observe that Teleodus (Brontops) avus of 

 the Oligocene has grinding teeth similar in size to 

 those of P. superhum. 



Inferior dentition. — The canines and grinding teeth 

 are preserved in the type jaw, but the incisor series is 

 wanting. They represent a specific progression upon 

 those of P. emarginatum in their greater size; in the 

 abbreviation of the postcanine diastema; in the 

 lengthening and broadening of the true molars, a 

 progressive tendency that may be followed from 

 Eotitanops through Manteoceras and Protitanotherium up 

 into the Oligocene titanotheres ; in the arrested length 

 of the premolar series; and in the more pronounced 

 hypsodonty of the cusps of the premolars and molars. 



Considered in detail, the inferior canines are seen to 

 be relatively closer together than those of either 31. 

 manteoceras or P. emarginatum, which are presumably 

 near the ancestral types of P. superhum; but they 

 retain the characteristically robust fangs and the 

 stout recurved crowns with gen er all 3^ rounded section, 

 faint anterior and posterior cingula. The basal crown 

 measurements of the canines are anteroposterior 32 

 millimeters, transverse 31. The postcanine diastema 

 is relatively reduced and uneven on the two sides — ■ 

 namely, 30 millimeters on the left, 20 (estimated) on 

 the right. 



The premolar series (PI. LXIX) is closely continuous, 

 measuring 105 millimeters. Pi of the left side was 

 apparently somewhat smaller than pi of the right. 

 Nothing remains of the crown of this tooth except the 

 laterally compressed subsecant talonid. P2 (ap. 28 

 mm., tr. 16) is distinguished from that of M. manteo- 

 ceras by the deepening of the crescents and the more 

 decided accent of the internal cusps, which are analo- 

 gous to the paraconid, metaconid, metastylid, and 

 entoconid on the molars. P3 (ap. 28 mm., tr. 18) is a 

 slightly longer and decidedly broader tooth than in 

 P. emarginatum; it is little if any more progressive 

 in the development of the cusps analogous to the 

 paraconid, metaconid, metastylid, and entoconid of the 

 molars, which, being less worn down than in the type 

 of P. emarginatum, produce at first the impression that 

 they mark a higher stage of evolution, but the diJSfer- 

 ences seem to be due largely to difference in wear; 

 however, the entoconid of the right side only is some- 

 what better developed than in P. emarginatum. P4 

 (ap. 33 mm., tr. 21) is still more decidedly molari- 

 form, the median internal cusp ( = metaconid) being 

 much more prominent than in either of the preceding 

 teeth, a feature foreshadowed in M. manteoceras. 



The true molars are decidedly longer and broader 

 than those of P. emarginatum. This progression in 



size and especially in width points toward brachy- 

 cephaly. There is a somewhat stronger accent of the 

 paraconids than in P. emarginatum, but this may result 

 from the greater wear in the type of that species, which 

 would depress the metaconids and entoconids nearer 

 to the level of the paraconid. The metastylid ridges 

 do not appear very prominent. The external cingu- 

 lum tends to festoon the sides of the protoconids and 

 hypoconids in a faint line, whereas in P. emarginatum 

 the cingulum is straighter and is thus (by comparison 

 with other titanotheres) seemingly more advanced 

 than in P. superhum. The outer surface of the ecto- 

 loph is entirely smooth on the median portion of the 

 lobes — that is, the cingulum has disappeared. The 

 measurements, in millimeters, are as follows: Mi, ap., 

 52; tr., 27 through trigonid, 30 through talonid. M2, 

 ap., 63; tr., 35 through trigonid, 36 through talonid. 

 M3, ap., 95 (estimated); tr., 40 through trigonid, 

 38 through talonid. 



Superior molars. — The second and third superior 

 molars of the same individual (PL LXIX) are almost 

 certainly associated with the type lower jaw; they have 

 the proper dimensions to fit the lower molars, and in 

 this jaw, as in others, they show more dentine than the 

 lower teeth; they are quadrate in form, m- measuring 

 57 by 57 millimeters and m^ 62 by 62. They exhibit 

 imperfectly developed external cingula and an internal 

 cingulum , which faintly festoons the inner cusps of the 

 crown. The features of m^ are the complete wearing 

 out of the prefossette, the somewhat median position 

 of the protocone, and the somewhat detached and 

 anteroposteriorly compressed hypocone; it is note- 

 worthy that, as in other titanotheres, while the ex- 

 ternal crescents are extremely worn the internal cones 

 are very slightly worn, the protocone barely exhibit- 

 ing exposure of the dentine at its apex. M^ shows the 

 bottom of the prefossette, a very large protocone, and 

 an angulate hypocone region, in which, however, there 

 is a sessile cingulum but no rudiment of the hypocone 

 proper. 



Comparison of teeth of Protitanotherium with those 

 of other genera. — Protitanotherium is at once distin- 

 guished from Teleodus avus of the lower Oligocene by 

 the character of the incisors, which in Protitanotherium 

 are large and more or less flat-topped and in Teleodus 

 smaller, with ovoid or hemispherical tops. The canines 

 of Protitanotherium are more robust, especially at the 

 base; those of Teleodus are more slender, erect, and 

 evenly sloping. The premolars of Protitanotherium 

 are in a lower stage of evolution — that is, they are less 

 molariform than those of Teleodus and Brontops. 



The jaw. — The dimensions of the jaw of P. superhum 

 (type) considerably surpass those of Brontops hrachy- 

 cephalus, from the lower Titanotherium zone, the length 

 from condyle to incisive border being 580 millimeters 

 and the depth of the angle below the condyle 270, as 

 against 490 and 220, respectively, in a small B. 



