EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



403 



(1885.1, pi. 52, fig. 3), appears to have had but one root. 

 P2 is shorter anteroposteriorly and less compressed 

 than in the typical D. hyognathus; its posterior V is 

 also smaller as compared with the protoconid and less 

 sharply developed. P3 is not preserved. P4 is also 

 less compressed, the posterior V lower and more 

 primitive in form than in D. hyognaihus. The true 

 molar series is considerably shorter, but the posterior 

 half of ms and especially the hypoconulid are relatively 

 longer and more compressed. The space between ms 

 and the ascending ramus was less. Comparative 

 measurements are as follows : 



Measurements of Dolichorhinus vallidens and D. longiceps? , in 

 millimeters 



Front of canine to hinder border of ma 



Front of pi to hinder border of mj 



Length of true molar series 



P2, ap. by tr 



P4, ap. by tr 



M3 (anterior lobe) , ap. by tr 



M3, length of hypoconulid 



D. vallidens, 

 Am. Mus. 

 6098, lecto- 

 type jaw 



230 



146 



123 



19X11 



23X13 



55X20 



14 



D. longiceps?. 



Am. Mus. 



1852 



275 



165 



139 



23X11 



25X15 



60X23 



15 



The specimen under consideration is distinguished 

 from jaws of M. manteoceras by the longer molar 

 series and more elongate hypoconulid on ms. 



Upper teeth of the paratype of Dolichorhinus vallidens 

 (Am. Mus. 5097). — The characters of the premolar 

 ectolophs are so constant in all the many specimens of 

 D. hyognathus that the marked differences which they 

 present in the paratype of D. vallidens, approaching as 

 they do the characters of the Mesatirhinus premolars, 

 appear to establish the specific separation. 



The whole series of upper grinding teeth (p'-m^) of 

 D. vallidens is estimated at 185 millimeters, as compared 

 with 177 in D. intermedins and 206 in D. hyognathus. 



Comparison with Dolichorhinus hyognathus. — As 

 noted above, the superior grinding series is shorter 

 than that of D. hyognathus (185 mm. (estimated), as 

 compared with 206), and the detailed anteroposterior 

 and transverse measurements of the crowns of the only 

 perfectly preserved teeth, p^, p'*, are practically identi- 

 cal with those of the average D. hyognathus, as shown 

 below : 



Measurements of upper premolars in species of Dolichorhinus, in 

 millimeters 



P^ anteroposterior 



P^ transverse 



P^, anteroposterior 



P^i transverse 



P', internal lobe, anteroposterior 

 P*, internal lobe, anteroposterior 



15 

 9.8 

 20 

 22 

 21 

 23 



The linear ectoloph measurements of the true molars 

 are intermediate between those of D. intermedins 

 and D. hyognathus. The ectolophs of the premolars 

 of D. vallidens (fig. 341, B) afford the most distinctive 

 character — namely, the broad festoon and the basal 

 spreading of the convexities of the protocone, a primi- 

 tive character which relates these teeth to the Mesati- 

 rhinus stage. The deuterocones of p^"* are more 



D 



A 



Figure 341. — Upper premolars of Mesatirhinus, Dolichorhinus, 

 and Metarhinus 



Outer side view. Natural size. A, Mesatirhimis petersoni, British Mus. (formerly 

 Am. Mus. lo5G), Big Bone Mountain, Henrys Fork, Bridger Basin, Wyo., 

 Bridger D; B, Dolichorhinus vallidens, Am. Mus. 5097 (paratype), reversed, 

 Mammoth Buttes, Bitter Creek, Washakie Basin, Wyo., Washakie B; C, 

 DolicliorJiinus hyognathus, Am. Mus. 1850, White River, Uinta Basin, Utah, 

 Uinta B 2; D, Metarhinus fiuviatilis. Am. Mus. 1946, White River, Uinta Basin, 

 Utah, Uinta B 1. 



primitive and the tritocones are more flattened than 

 in' the D. intermedius type. 



These characters tend to show that so far as indi- 

 cated by the paratype D. vallidens is somewhat more 

 primitive than either D. intermedius or D. hyognathus. 



Comparison with M. petersoni and other forms. — The 

 superior grindiag teeth of this paratype resemble 

 those of certain specimens of M. petersoni on a larger 

 scale. The progressive distinctions are (a) the pres- 

 ence of a cingulum on the inner side of p'; (6) the 

 quite complete cingulum on the inner side of p^ and 

 p* and the somewhat more flattened and elevated 

 ectolophs of p^~^, which are less elevated, however, 



