EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



349 



long and deep maxillary union so characteristic of 

 D. hyognathus. The nasals are much less thickened 

 and decurved at the sides than in D. hyognathus. This 

 aspect of the skull also exhibits the depth of the 

 zygoma, including the malar and squamosal portion, 

 compared with the extreme shallowness of this arch 

 in D. hyognathus. 



The occipital view of the skull is still more charac- 

 teristic, owing to its great height (194 mm.) as com- 

 pared with its breadth (137 mm.), also to the pres- 

 ence of a pair of oval prominences on either side of 

 the superior portion of the foramen magnum, as in 

 Menodus giganteus. This view also illustrates the 

 breadth of the paroccipital and postglenoid processes. 



The dentition is finely represented in the complete 

 type skull (Am. Mus. 2060) and in a somewhat more 

 progressive stage in the paratype, consisting of the 

 anterior portion of a skull (Am. Mus. 2004). 



The incisors are superbly shown in Am. Mus. 2004 

 and 2060 (PL LV; figs. 294-297). The superior in- 

 cisors in the type are pointed, decidedly cingulate or 

 cupped posteriorly, and sharply convex anteriorly, and 

 increase in size rapidly from i' to i'; the lateral incisor 

 (i^) is more caniniform than incisiform; the crown of 

 i' measures 15 millimeters vertically, and a slight ridge 

 extends down the posterior face to the apex of the 

 basal cingulum which branches on either side to form 

 lateral depressions; the crown of i^ (measuring 19 mm. 

 vertically) is slightly larger and of exactly similar 

 form; in i^ the caniniform crown (measuring 28 mm. 

 vertically) is distinguished on its postero-internal sur- 

 face by a lanceolate face with sharply defined antero- 

 internal and postero-external ridges, which sweep at the 

 base into the low, broad cingulum, exactly as in the 

 canine. In Am. Mus. 2004 the superior incisors are 

 even larger and the posterior cingulum is more strongly 

 accented. All the cutting teeth, both incisors and 

 canines, bear a striking similarity to those of T. cultri- 

 dens and T. validum — in fact, they are almost directly 

 progressive upon them, the only difference being that 

 the posterior angles and cingula are a little less sharply 

 accented. The inferior incisors are not known. 



The superior tusks, which are completely preserved 

 only in the paratype (Am. Mus. 2004), are much more 

 decidedly of the lanceolate, typical Telmatherium 

 type than those of M. manteoceras, although the 

 anterior and posterior ridges are not quite so promi- 

 nent and sharply defined as in T. cultridens, T. validum, 

 or D. hyognathus; the tusks are none the less long 

 (43 mm.) and transversely narrower (22 mm.) at the 

 base of the crown than those of M. manteoceras 

 (25 mm.); the ridges pass inferiorly into a strong 

 postero-internal cingulum, which also clearly dis- 

 tinguishes these tusks from those of other species 

 so far as observed. The superior molar-premolar 

 series as a whole is not only larger (229 mm. in Am. 

 Mus. 2004) but has a very marked individuality 



throughout, so that every tooth in the series can be 

 distinguished by careful observation from those of 

 either M. manteoceras or D. hyognathus. The type is 

 distinctly telmatherioid, exhibiting peculiar pro- 

 gressive modifications upon the dental type of T. 

 cultridens and T. validum which partly anticipate 

 those seen in Menodus. The series in the type 

 (Am. Mus. 2060) is of somewhat smaller size and in an 

 earlier or less progressive stage than that in Am. 

 Mus. 2004. In both specimens the breadth of the 

 molars equals or slightly exceeds the length, whereas 

 in the more dolichocephalic D. hyognathus molars the 

 length decidedly exceeds the breadth. The dental 

 proportions are therefore mesaticephalic. 



Premolars. — The superior premolars of the type are 

 so much worn as to obliterate certain of their rudi- 

 mentary progressive characters. The following de- 

 scription of these parts is accordingly based upon the 

 unworn premolars of the paratype specimen, which 

 appears to be in a somewhat more progressive stage of 

 evolution. A narrow diastema, 12 to 16 millimeters. 



Figure 297. — Paratype skull of Telmatherium uUimum 



One-fourth natural size. Am. Mus. 2004, reversed; White River. Uinta Ba.sin, 



Utah; Uinta C, true Uinta formation. 



separates the canine from p^ The premolar series, 

 measuring 90 (type) and 95 (paratype) miUimeters, 

 as compared with 82 in M. manteoceras, exhibits not 

 only increase in size but marked progression in pattern, 

 as seen in the following characters: (1) Slightly in- 

 creased compHcation of p^ (ap. 19 mm., tr. 12) in the 

 rudimentary internal cingulum and more decided 

 elevation of the tritocene; (2) in p^ to p* of the para- 

 type (No. 2004) the deuterocones consist of antero- 

 posteriorly elongate ridges, much more pronounced 

 than in T. cultridens, convex on the lingual and 

 flattened on the buccal surfaces, totally different 

 from the smooth-sided deuterocones of M. manteoceras 

 and from the apically compressed cones with faint 

 lateral ridges in D. hyognathus; this feature, it should 

 be added, is much more distinctly exhibited in the 

 Httle worn series of Am. Mus. 2004 than in the much 

 worn series of the type, Am. Mus. 2060; (3) this deu- 

 terocone ridge is destined to give rise to the tetarto- 

 cones by constriction, and in p^ p** a faint rudiment of 

 the postero-internal cingulum can be observed in the 

 unworn crown; (4) the internal cingulum is faintly 

 defined around the entire lingual surface of the deutero- 



