EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



341 



Measurements of skull and teeth of species of telmatheres, in 

 ■millimeters 



Basal length of skull 



Zygomatic breadth of 

 skull 



Length of dental series 



Pi-m3 



P'-p< 



M'-m3 



I', ap. by tr__ 

 P, ap. by tr_. 

 C, ap. by tr__ 

 P*, ap. by tr_. 

 M', ap. by tr_ 

 IVP, ap. by tr_ 



255 



180 



80 



103 



9X 8 



MX 13 



20X ? 



21X26 



29X29 



36X39 



270 



79 



113 



UX 9 



22X30 

 30X30 

 39X38 



330 



295 



207 



82 



128 



22X21 



25X22 



27X24 



22X36 



38X38 



38X43 





S5. 

 as 



300+ 



305 



218 

 89 



130 

 14X14 

 19X18 



25X35 

 38X40' 

 46X52' 



229 

 95 



137 

 14X14 

 22X20 

 2.5X 22 

 27X35 

 40X37 

 49X48 



The history of this species has already been given. 

 (See pp. 167-168.) 



Materials. — As noted above, the type (Princeton 

 Mus. 10027) is from the Bridger Basin, Henrys 

 Fork Hill, level C or D. It represents a smaller and 

 considerably more primitive animal than T. validum, 

 especially in the more incisiform character of the 

 superior lateral incisor. Another specimen from 

 Bridger C 2 referable to this species (Am. Mus. 12209) 

 consists of p"*, m', and m^ Another specimen that is 

 certainly referable to this species is a young lower jaw 

 (Am. Mus. 1560), with ms not yet entirely exposed, 

 recorded from Twin Buttes, level Bridger C or D. 

 Another well-preserved lower jaw (Am. Mus. 12193), 

 from Henrys Fork, level Bridger C 3, agrees closely 

 with the type in the dentition. Am. Mus. 12685, 

 which includes m\ with a deciduous molar, and an 

 unerupted p-, from Sage Creek Spring, level Bridger 

 C 3, may represent a primitive phase of this species. 

 A lower jaw (Am. Mus. 12687) from Henrys Fork Hill, 

 level Bridger D 3, is somewhat more progressive than 

 the type in p2 and ps. Another specimen from the 

 Bridger Basin (Am. Mus. 1546a), consists of pMn^, 



B "=^ C 



Figure 289. — Progressive hypsodonty of the molars in Telmaiherium 

 Natural size. Posterior view of third left upper molar. A, T. cuUridens, upper Bridger (C or D) ; B, T. ralidum, Bridger D; C, T. uUimum, Uinta C (true Uinta) . 



The table illustrates (1) the marked increase in the 

 size of the skull and dentition as we pass from T. 

 cultridens of the upper Bridger to T. ultimum of 

 Uinta C; (2) the relatively larger size, in the later 

 stages, of the true molars as compared with the pre- 

 molars; (3) the increase in both the length and the 

 breadth of the molars. 



Telmatherium cultridens (Osborn, Scott, and Speir) 



(? Leurbcephalus cultridens) 



Plates LV, LXIII, LXV; text figures 101, 223-226, 289-293, 

 735 



[For original description and type references see p. 168] 



Type locality and geologicliorizon. — Henrys Fork Hill, 

 Bridger Basin, Wyo.; Bridger formation, level C or D. 

 Also recorded from Bridger C 2 and probably other 

 horizons, as described below. 



Specific characters. — P'-m', 180 millimeters. In 

 males superior canines elongate (46 rnm.), laterally 

 compressed; premolars less progressive than in T. 

 validum. 



right and left, and the lower border of the orbit. 

 It differs from the type in the more complete exter- 

 nal cingulum on p*, but the malar closely resembles 

 that of the type. This specimen also approaches 

 M. manteoceras in some respects. A young lower jaw 

 from the Washakie Basin (Am. Mus. 2356), with the 

 milk molai's in place, is more advanced than the type 

 in the characters of the permanent p2. 



Type of T. cultridens. — So little is preserved of the 

 cranium of this type (Princeton Mus. 10027) that it 

 can only be partially characterized. As shown in 

 Figure 290 there is a slight concavity at the side of 

 the face and distinct evidence of the existence of a 

 nasofrontal horn rudiment. The premaxUlary in side 

 view approaches the Manteoceras type but is dis- 

 tinguished by the greater depth and by the emphasis of 

 the dorsal symphyseal keel. It is more elongate and 

 more angulate superiorly than the short, rounded 

 premaxillary of Palaeosyops and is vertically deeper 

 than in Mesatirhinus, Metarliinus, and Dolichorhinus. 

 Its dimensions are, depth from symphyseal crest to 



