EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



353 



physisis extremely long (200 mm.); it is both, actually 

 and relatively longer than in P. emarginatum (155) or 

 P. superhum (158, estimated). The jaws are de- 

 cidedly deep, measuring 107 millimeters below p2, 124 

 behind m2. The coronoid was probably elevated, ta- 

 pering, and recurved toward the summit. The thick- 

 ness of the rami in the type jaw has been reduced by 

 crushing; below mi it is 40 millimeters. This jaw 

 therefore represents a large but fairly slender and 

 active animal, which in some respects is suggestive of 

 relationship with species of the long-jawed genus Meno- 



ently short, broad proximally, and tapering distally; 

 face concave in front of orbits; frontonasal "horn 

 swellings" not evident; sagittal crest deep and nar- 

 row; occiput low with thin crests; dentition extremely 

 macrodont; incisors relatively larger than in any other 

 known titanothere. 



Historical notes.^ln describing the type species 

 {Sthenodectes incisivus) of this genus the author, Earl 

 Douglass (1909.1, p. 305), said: "I think that this skull 

 represents a different genus from Telmatherium, but I 

 prefer to place it provisionally here rather than estab- 



FiGURE 300. — Lower jaws of Telmatherium ullimum and T. altidens 



One-fourth natural size. A, T. ultimum, Am. Mus. 2060 (type), reversed; White River, Uinta Basin, Utah; base of Uinta C, true Uinta 

 formation. B, T. altidens, Am. Mus. 2025 (type); White River, Utah; Uinta C. 



dus of the Oligocene but in other respects is very unlike 

 an ancestor of Menodus — namely, the excessively large 

 size of the incisors, the retarded condition of pi and 

 P2, and the very long postcanine diastema. 



Sthenodectes Gregory 

 Plates LXV, LXVI; text figures 129, 130, 301 



[For original description and type references see p. 190] 



Generic cTiaracters. — Skull mesaticephalic or sub- 

 brachycephalic; cephalic index 62-65; malars with- 

 out infraorbital shelf or protuberance; nasals appar- 



lish another genus." Through the courtesy of Doug- 

 lass, Gregory (1912.1) was enabled to compare this 

 type with the extensive material in the American and 

 Yale Museums and reached the conclusion that T. 

 incisivum represents a different genus or subgenus, to 

 which he gave the name Sthenodectes, in allusion to 

 the great power and development of the incisors and 

 canines. The following characters were assigned by 

 Gregory in the original description of the genus as 

 compared with Telmatherium: (1) The incisors are much 

 larger and more advanced in evolution; (2) the post- 



