EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



377 



The canines are intermediate in form between the 

 Manteoceras and Brontops types, perhaps nearer 

 Brontops, and were evidently robust fighting weapons. 

 Unfortunately the form of the superior and posterior 

 parts of the skull is still unknown. 



D 



Figure 318. — Nasal region in three specimens of Protilanotherium 



Top view. One-fourth natural size. A, X), P. emarginatum, Princeton Mus. 11242 (type); B 

 iuperbumf, Carnegie Mus. 2855; C, P. superbumf, Princeton Mus. 11213. 



Protitanotherium emarginatum Hatcher 



[Diplacodon emarginatus Hatcher, p. 177] 



Plates LXVni, LXIX; text figures 24, 29, 87, 112, 314-320, 

 374, 375, 408, 648, 649, 712 



Type locality and geologic horizon. — Kennedys Hole, 

 8 miles north of White River and 25 miles east of Ouray 

 Agency, Uinta Basin, Utah; Uinta formation {Dipla- 

 codon-Protitanotherium-EpiMppus zone, Uinta C). 



Specific characters. — Pi-ms 294 millimeters (esti- 

 mated), pi with a small talonid; ii small, round-topped; 

 is large, bluntly pointed ; ia much larger than is. Lower 

 canine more erect, recui'ved, and abruptly swelling at 

 the base. Postcanine diastema short (27 mm.) but 

 relatively longer than in P. superbum. Lower pre- 

 molars and molars more brachyodont, with sloping 

 curves. 



P. emarginatum appears to be closely allied to P. 

 superbum but is apparently a lower stage, distinguished 



by its smaller size, more brachyodont premolars and 

 molars, and more erect recurved lower canines, which 

 swell more rapidly at the base. 



Materials. — This species is represented by the 

 type (see below), by the finely preserved anterior 

 portions of a jaw in the Yale Museum 

 (No. 635 D), and by a fairly well preserved 

 jaw in the American Museum (No. 2028). 

 The jaw in the Yale Museum is especially 

 valuable because it includes, besides the 

 incisors, canines, and portions of the pre- 

 molars, a complete ma, a tooth which is 

 imperfect in the type. 



Skull. — The type of the present species, 

 discovered by Hatcher himself, is the an- 

 terior portion of a skull and lower jaw 

 (Princeton Mus. 11242). Hatcher noted 

 the greater size of this animal than Dipla- 

 codon elatus as indicated by the length of 

 the grinding teeth (294 mm., as compared 

 with 244). So far as preserved the dorsal 

 surface of the skull is concave anteroposte- 

 riorly and suggests the broad, fiat frontal 

 region and flattened parietal vertex of the 

 Oligocene forms. The nasal openings are 

 high and deeply incised. The horns are 

 composed of the frontals overlapping the 

 nasals; they are placed longitudinally and 

 directed upward, outward, and forward. 

 The nasals are broad, strong, and rather 

 short, firmly coossified, concave inferiorly; 

 they measure in free length 107 millimeters 

 and in greatest breadth 123. The specific 

 name P. emarginatum, refers to the fact that 

 the nasals are "emarginate anteriorly," but 

 they are not deeply indented in the 

 midline, as in a larger pair of nasals also 

 described by Hatcher (fig. 318) which may 

 be referred provisionally to P. superbum. 

 The premaxillaries are well developed and separated 

 anteriorly by a deep median 

 notch, below which they are 

 firmly coossified. The maxilla- 

 ries are expanded at the base of 

 the canines and decidedly con- 

 stricted between these teeth and 

 p'. The postcanine diastema 

 measures 37 millimeters, and 

 back of this the maxillaries ex- 

 pand rapidly in order to ac- 

 commodate the large posterior 

 premolars and molars. The in- 

 fraorbital foramen was probably 

 situated just above p*, as in 

 Palaeosyops, Limnohyops, Tel- 

 matherium, and Manteoceras. In Mesatirhinus and 

 Dolichorhinus it is more nearly above m^ 



Figure 319. — Sections 

 of the nasals and 

 horns of Protitano- 

 therium einar gi- 

 natum 



Princeton Mus. 11242 (type). 

 One-seventh natural size. 



