266 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



spreading feet, and to judge from the associated fauna 

 in comparison with that of the Uving tapirs it inhab- 

 ited semitropical forests, especially those near streams. 

 Dolichocephalic types. — The other extreme of struc- 

 ture among Eocene titanotheres is the long-skulled 

 Dolichorhinus, which succeeds Palaeosyops in geologic 

 time, belonging more to the upper Eocene. The 

 muzzle of this animal (fig. 219) was rather expanded 



The cheek teeth were relatively long-crowned with 

 pointed cusps and constituted a relatively elaborate 

 cutting and triturating apparatus, as compared with 

 the very short-crowned grinders of Palaeosyops. The 

 excursion of the more slender mandible was partly 

 vertical, partly oblique. The oblique position of 

 the grinding teeth produced an oblique shearing 

 action. Conditioning these changes the length and 

 proportions of the masticating muscles 

 and their angles of action were also 

 changed. (See Chaps. V, VIII for de- 

 tails. 



These features of the head of Dolicho- 

 rhinus indicate that the food of this 

 animal required finer cutting and better 

 trituration than that of Palaeosyops. 

 Although in no sense a grazing animal 

 as compared with the grazing Equidae 

 and Bovinae, Dolichorhinus was better 

 adapted to grazing than Palaeosyops. 

 Its remains are very frequently found in 

 coarse sandstones laid down by rapid 

 streams, and it may well have hved partly 

 in the rivers and along their banks. 



Intermediate types. — The other Eocene 

 titanotheres, such as Manteoceras (fig. 

 220, C) and Telmatherium (fig. 220, B) 

 are more or less intermediate between 

 these extremes in the form of the head. 

 Thus Manteoceras has very heavy, 

 almost boarlike tusks and large, blunt 

 incisor teeth, together with cheek teeth 

 that are more elongate than those of 

 Palaeosyops. Telmatherium had much 

 more trenchant canine tusks, pointed 

 incisor teeth, and somewhat elongated 

 grinding teeth. 



ORIGIN AND STRUCTURE OF THE 

 IN TITANOTHERES 



'HORNS" 



-Heads of Eocene titanotheres of four phyla 

 Modeled by Charles R. Knight. A, Palaeosyops, brachycephalic; B, Telmatherium, mesaticephalic; C' 

 Manteoceras, mesaticephalic; D, Dolichorhinus, dolichocephalic. The nostrils were actually more 

 nearly terminal than those shown in the models, and the upper lip may have been more markedly 

 pointed or prehensile. H, Horn rudiments. 



or truncate. The incisors were arranged in a semi- 

 circle and made some approach to the cropping in- 

 cisors of a ruminant, being also partly cupped as in 

 Oligocene species of the horse. The space behind 

 the canine tusk was longer, as in typical herbivorous 

 forms. The canines were recurved, compressed, or 

 sharp-edged and may have been used in fighting, 

 as in the camels. The offensive power of the front 

 teeth was, however, much less than in Palaeosyops. 



The so-called horns of titanotheres 

 arise as rectigradations; they consist of 

 osseous protuberances of the skull above 

 the eyes, where the frontals overlap 

 the nasal bones. In life they were prob- 

 ably covered with tough sldn, rather than with horn. 

 In the earliest titanotheres, of lower Eocene age {Lamb- 

 dotherium, Eotitanops), the frontonasal junction shows 

 no beginning of the horns. In the genera Palaeosyops 

 and Limnohyops (middle Eocene) most of the skulls 

 were equally hornless, but some very old males of 

 Palaeosyops show an incipient nasofrontal protuber- 

 ance and roughening of the outer tabula of the bone. 

 (See PI. XVI.) In the middle Eocene contemporary 



