344 



TITANOTHERES OF ANCIENT "WYOMING, DAKOTA, AND NEBRASKA 



the apices being only 12 millimeters apart. M' ex- 

 hibits a rudimentary hypocone, also a rudimentary 

 swelling of the anterior cingulum corresponding with 

 the protostyle of T. ultimum and Menodus. The in- 

 ferior molars constitute a long, narrow series (122 

 mm.) in the type specimen and exhibit distinctly 

 defined paraconids as well as rudimentary metastj^- 

 lids and entostylids. In the elongate nis (54 by 22 

 mm.) the apex of the hypoconulid is placed nearly in 

 line with the outer wall, and this cone is deeply cres- 

 centic within. 



Mechanical correlation oj upper and lower teeth. — The 

 significance of these accessory cuspules as well as the 

 mechanical relations of the upper and lower cusps is 

 well demonstrated in the accompanying drawings 

 (figs. 291, 292), which show that the metastylid be- 

 low serves to press the food against the protocones 

 and their ascending internal cingula ebove. The 

 adaptive significance of these minute features in the 

 comminution of the harder food which was probably 

 selected by this species is thus clearly brought out. 



Figure 293. — Lower jaw of Telmatherium cuUridens 



One-fourth natural size. Am. Mus. 1560. Twin Buttes, Bridger Basin, Wyo.; 

 upper part of Bridger formation (Bridger C or D). 



It is seen also that the entoconid and paraconid 

 below press the food against the hypocones above, 

 that the tip of the hypocone fits squarely into the 

 antero-internal part of the basin of the trigonid, that 

 the single deuterocones of the superior premolars fit 

 into the posterior internal valleys (=talonids) of the 

 inferior premolars, and that the elongate p^ above is 

 effectively correlated with the elongate and secant 

 P2 below. 



Millc dentition of fT. validum. — A pair of young 

 jaws from the Washakie Basin (Am. Mus. 2356) 

 exhibit dp2, dps, dp^, m', nr in place, with the true 

 premolars as well as nis still deeply buried in the jaw. 

 Each of the deciduous premolars is fully molariform, 

 with sharply defined double crescents; precocious 

 molarizatiou is, in fact, characteristic of mUk pre- 

 molars of titanotheres in general. Dps measures 

 (ap. by tr.) 19 by 11 millimeters, dp4 24 by 14. The 

 enamel is vertically crenulate on the outer surface. 

 An important fact is that this jaw is in a more ad- 

 vanced stage of evolution than the type of T. cul- 

 tridens, since the second permanent premolar (P2) 



has the talonid V much better developed, and it 

 may therefore belong to T. validum. 



Lower jaw of Telmatherium cultridens. — The par- 

 tially preserved type jaw (fig. 292) exhibits (1) two 

 mental foramina, the second indistinctly shown, the 

 larger and more anterior being below p^; (2) a gradual 

 increase in depth from 58 millimeters behind p2 to 65 

 behind m2 and 76 behind nia, with a thickness of 20 

 millimeters below mo. 



A more perfectly preserved young jaw (Am. Mus. 

 1560, fig. 293) in which ms is not fully emerged 

 exhibits a long (91 mm.) and rather shallow (26 mm.) 

 symphysis and laterally compressed chin (47 mm.); 

 the ramus exhibits two mental foramina and gradually 

 increases in depth from 51 millimeters behind pa to 58 

 behind m2 (inside), the thickness being 19 millimeters 

 below m2. All these measurements would naturally 

 increase with advancing age. The depth of the angle 

 below the condyle is 134 millimeters; the coronoid 

 attains a free height of 49 millimeters and is regularly 

 hooked or recurved from base to tip. The angle is 

 thin but extended downward and backward very 

 decidedly, as in Manteoceras manteoceras. Compari- 

 son with Am. Mus. 12193 (Bridger C 3), which prob- 

 ably belongs with this species, brings out the differ- 

 ences due to age. In the younger jaw (Am. Mus. 

 1560) the chin and ramus are shallower, the whole 

 ascending ramus narrower, the angle less depressed, 

 the coronoid shorter, more delicate and recurved, less 

 truncate at top, and with the lateral flange much less 

 pronounced. 



Measurements of Am. Mus. 12193 are as follows: 

 Pi-ms, 194 millimeters; pi_4, 68; mi_3, 125. 



Telmatherium validum Marsh 



Plate LXIV; text figures 93, 289 

 [For original description and type references see p. 160] 



Type locality and geologic horizon. — Bridger Basin, 

 Wyo.; Bridger formation, Uintatherium-Manteoceras- 

 Mesatirhinus zone, level Bridger D. 



Specific characters. — P'-m^, 195 millimeters. In 

 males, superior canines large, elongate (55 mm.), 

 lateral superior incisors subcaniniform; ectolophs of 

 superior premolars with sharply cingulate ridges; pre- 

 molars more progressive than in T. cultridens; trans- 

 verse measurements of p'-m' greater than in T. cultri- 

 dens. Frontonasal region unknown. 



The only teeth definitely known are those of the 

 type in the Yale Museum (No. 11120), a male indi- 

 vidual first characterized by Marsh in 1872 and fully 

 discussed later by Earle. The animal is young, since 

 the crown of the last molar is entirely unworn, and all 

 the distinctive characters of the surfaces of the teeth 

 are still sharply defined. As noted above in the 

 description of Palaeosyops these surface characters 

 disappear rapidly by the wearing action of the food. 



The type specimen represents a comparatively large 

 and powerful animal. The canines, relatively more 



