EVOLUTION OP THE SKULL AND TEETH OF EOCENE TITANOTHERES 



437 



Measurements in millimeters 



" Approximate measurements. 



MANDIBLE 



[Fig. 3C5] 



The lower jaw is somewhat depressed by crushing, but 

 allowing for this fact, it appears that the horizontal ramus of 

 Diploceras osborni is shallower than in P. emarginatum. Char- 

 acteristics which may further be noted are the more rounded 

 under surface of the symphysis and the constriction of the lower 

 jaws in the area between the canine and the premolars, which is 

 greater than in P. emarginatum. As in the latter, the symphysis 

 is strong and the mental foramen is large, located well down 

 on the ramus, directly below P2. The lower jaw is broken 

 off back of ms. 



DENTITION 

 [Fig. 366] 



The upper incisors and canines are well preserved, though 

 much worn in the two crania under description. The molar- 

 premolar series is less completely preserved in No. 2858, while 

 in 2859 the superior dentition is completely represented. The 

 lateral incisor and the canine of the right mandible and the 

 complete molar-premolar series of the left ramus are also 

 present in the latter individual. 



As stated above, the median upper incisors are widely 

 separated by the deeply excavated median notch of the pre- 

 maxillaries. As seen in the illustration, the incisor series is 

 placed well in front of the canine and the arc of the circle, 

 which their arrangement represents, is more convex than in 

 P. emarginatum. Their crowns are nearly circular in outline, 

 covered with a heavy coat of enamel, bluntly conical, with a 

 prominent cingulum at their posterior bases. They perhaps 

 increase in size more gradually from i' to i^ than in P. emar- 

 ginatum. The canine is relatively smaller than in the latter 

 genus, which imparts a much lighter looking aspect not only 

 to this region of the dentition but also to the entire outline of 

 the anterior portion of the muzzle in the paratype. No. 2858, 

 as well as in the type. No. 2859. Furthermore the crown of the 

 canine (especially in No. 2859) is shorter, blunter, and the 

 lateral ridges are less developed in the present species than in 

 either P. emarginatum or Diplacodon elatum. D. elatum has 

 the canine more nearly of the same proportion as in P. emar- 



ginatum. The diastema back of the canine is relatively longer 

 and its border much thinner than in P. emarginatum, in which 

 respect it is more nearly like Diplacodon elatum. 



The crown of pi is so much worn that its characters can not 

 be made out. It is, however, of greater anteroposterior than 

 transverse diameter and undoubtedly had a simple structure 

 like that of P. emarginatum. P^ is also much worn, especially 



Figure 366. — Nasals and horn swellings of Eotitanotherium 

 osborni 



One-fourth natural size. Ai, Carnegie Mus. 2859 (type), Duchesne River near 

 Myton, Uinta County, Utah, Uinta B 2, top view; Aj, same, basal view; B, 

 Carnegie Mus. 2858 (paratype), locality and level same as A, top view. 



along the external portion. The external face of the ectoloph 

 is subdivided by a deep vertical groove and is much convex both 

 anteroposteriorly and supero-inferiorly. This deep groove adds 

 greatly to the anteroposterior convexity of the proto- and trito- 

 cones. The general outlines of the tooth are less quadrate than 

 in Titanotherium, which is apparently due to the lack of devel- 



