UNQULATA. 329 



period in North America, however, one peculiar group of 

 primitive perissodactyls arose, comprising large animals which 

 in the Miocene period rivalled the modern elephants in size 

 and then suddenly became extinct. This is the family of 

 Titanotheriidae or Brontotheriidae, which seems to have 

 been a comparatively local race confined to a limited region 

 of North America; for the only European fossils hitherto 

 claimed to belong to similar animals are merely fragments of 

 jaws and teeth too inconclusive for satisfactory discussion. The 

 grinding teeth are very low-crowned (brachyodont), and there 

 is nearly always a short diastema between the canine and the 

 premolars. In the upper molars (fig. 189) the two external 



FIG. 189. 



Second Bight Upper Molar of Titanotheriida;, two-thirds nat. size. M. Eocene 

 (Bridger Formation) ; Wyoming. 1. Palaosyops paludosus. 2. Limnohyops 

 laticeps. 3. Palteosyops minor, hy., hypocone ; me., metacone ; ml., meta- 

 conule ; pa., paracone ; pi., protoconule ; pr. , protocone. (After Earle.) 



cusps are merged into a W-shaped outer wall, while the inner 

 cusps are separate pointed tubercles ; in the lower molars the 

 crown consists of crescentic ridges, two in m. 1, 2, three in the 

 hindermost m. 3. In the Eocene genera (e.g., Palceosyops) all 

 the premolars are simpler than the molars, while in the 

 Miocene forms (e.g., Titanotherium) one or more of the pre- 

 molars approximate to the molars in complexity. The canines 

 and incisors are at first well developed, while later they 

 become much reduced, variable and rudimentary. The nasal 

 bones always project freely over the large narial opening, and 

 in the specialized Miocene genera they enter the base of a pair 

 of bony prominences which arise from the maxillae. The ilium 

 is expanded like that of the elephants, and the third trochanter 



