EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



345 



prominent than in T. ultimum, suggest a possible 

 affinity to T. altidens of Uinta C The lateral superior 

 incisors are almost as distinctly caniniform as in T. 

 ultimum. As compared with T. cultridens, distinctive 

 characters are the more progressive rectigradations, 

 seen principally in the premolar teeth, as enumerated 

 below, also the greater width of the premolars. From 

 M. manteoceras this animal is readily distinguished 

 by its very long and less curved canines. 



A comparison of the detailed measurements of the 

 teeth is given in the following table : 



Measurements of teeth in Telmatherium validum and T. cultri- 

 dens, in millimeters 



In T. validum the opposite superior incisor series 

 converge slightly. I' has an angulate antero-exter- 

 nal face and sharply defined postero-internal cingulum; 

 i^ is a larger tooth, with a broad and sharply defined 

 cingulum; while in i' we have a subcaniniform crown of 

 very large size, with compressed anterior and posterior 

 edges and somewhat less prominent internal cingulum, 

 sloping downward and backward. The inferior in- 

 cisors are not Icnown. 



The superior canine (55 mm.) is a powerful lance- 

 shaped tooth, larger but of the same form as in T. 

 cultridens, with a very convex antero-external and 

 more plane postero-internal face, bounded by the 

 sharply defined anterior and posterior ridges. 



The superior grinding series, including the spaced 

 p', extends 195 millimeters anteroposteriorly, as com- 

 pared with 180 in T. cultridens (both males). In 

 general, the teeth are similar to those of T. cultridens, 

 but besides the larger size we note the following pro- 

 gressive features: (1) On p' the internal cingulum is 

 well defined, with the rudimentary posterior cusp 

 larger; (2) p^ is slightly broader and shorter (ap. 24 

 mm., tr. 20); (3) there are protoconules on p^"*. The 

 protoconules on the true molars are the only variable 

 or reversional characters. 



P' is much larger than in T. cultridens. It is 

 separated by narrow intervals both from the. canine 

 (9 mm.) and from the second premolar. In p^ be- 

 sides the greater breadth we note the somewhat more 



anterior position of the deuterocone and the more sub- 

 equal convexities of the protocone and tritocone on the 

 ectoloph, although the base of the protocone is still 

 much broader than that of the tritocone; p^ has a 

 rudimentary protoconule but no suggestion of a 

 tetartocone. In p' we have a more quadrangular 

 crown with a more elevated ectoloph than in T. cul- 

 tridens, and a more symmetrical development of the 

 deuterocone and tritocone, although the former is 

 still widely expanded at the base. In both p^ and 

 p* the internal cingulum is slightly less complete than 

 in T. cultridens. On p** there is a very striking ele- 

 vation of the ectoloph accompanied by greater promi- 

 nence of the antero-external style and greater sym- 

 metry of the deuterocone and tritocone convexities. 



The molars represent a progression upon those of 

 T. cultridens, with sharp prominent styles, serrate 

 external cingula, elevated anterior cingula, pointed 

 protocones and hypocones, which are somewhat 

 flattened and vertically striated on their inner faces; 

 m^ has a prominent and serrate posterior cingulum 

 but no trace of a hypocone. 



Telmatherium ultimum Osborn 



Plates XVI, XLVI, LI, LV, LXV; text figures 126, 219, 223, 

 255, 256, 289, 294-298, 300, 508, 516, 592, 593, 647, 717, 745 



[For original description and type references, see pp. 177, 184. For slteletal 

 characters see p. 653] 



Type locality and geologic horizon. — White River, 

 Uinta Basin, Utah; Uinta formation {Diplacodon- 

 Protitanotherium-Epihippus zone, Uinta C 1). 



Specific characters. — Skull very large (basal length 

 510 mm.), zygomata arching (zygomatic breadth 300 

 mm., estimated). Incisors and canines large, i' very 

 large, subcaniniform. P'-m^ 218 millimeters (type); 

 premolars progressive; p^ p* with the two outer cusps 

 subequal and externally convex; well-developed 

 internal and nearly complete external cingula; very 

 rudimentary tetartocone swellings; molars large 

 (m'-m^, 129 mm.) and progressive. 



The discovery in Uinta C, by 0. A. Peterson, of a 

 female skull and jaw (Am. Mus. 2060) and the ante- 

 rior half of a male skull with well-preserved dentition 

 (Am. Mus. 2004) representing this species was a 

 most important one. The animal was at first sup- 

 posed by Osborn to be a terminal member of the 

 Palaeosyops series. Subsequently it was compared 

 point by point with Marsh's type of Telmatherium 

 validum and was found to exhibit the most striking 

 resemblances in the dentition and those parts of the 

 skull in which comparison could be made in both. 

 Highly distinctive is the premaxillary symphysis, 

 more deep and elongate than in Metarhinus, deeper 

 than in the type and paratype of Manteoceras 

 manteoceras, more abbreviate than in Dolichorhinus. 

 The region of the malars below the orbits is also 

 characteristic and similar to that of T. cultridens but 

 shows a more decided depression for the anterior 



