314 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



below; is have short roots and are being crowded out 

 byia. 



Canines. — The superior canines are rounded at the 

 base and when unworn are very sHghtly recurved and 

 sharply pointed, differing from those of Telmatherium 



Figure 266. — Lower jaws of Limnohyops and Palaeosyops 



One-fourth natural size. A, L. prisms. Am. Mus. 11688 (cotype), reversed; Grizzly 

 Buttcs (east), Bridger Basin, Wyo.; Bridger formation, level B 2; coronoid and 

 condylar region reconstructed. Bi, P. copeiT, Am. Mus. 12205a; Lone Tree, 

 Henrys Fork, Bridger Basin; level D 1, 15 feet above white stratum. Bj, The same, 

 section through mj. C, L. laticeps. Am. Mus. 12201,$, reversed; Henrys Fork 

 Hill, Bridger Basin, level C 4; angle restored from P. paludosus, Am. Mus. 11690 



in their circular section and strongly convex inner 

 sides. In females the canines are long, pointed, and 

 less robust, whUe in males they are much more rounded 

 and robust. The inferior canines are of very similar 

 form, nearly erect, with crowns rounded at the base, 



differing from those of Manteoceras in the absence ol 

 the marked posterior expansion of the base, and from 

 those of Telmatherium in the rounded, nonlanceolate 

 form. A peculiar feature of the lower canines is the 

 directly internal or lingual position of the posterior 

 ridge, the two ridges being thus brought very close 

 together. 



Premolars. — The law of cusp addition in the pre- 

 molars, which constitutes a most important means of 

 distinguishing the specific stages, is clearly set forth 

 above. In the general brachycephaly the premolars 

 acquire a rounded form rather than the elongate or 

 angulate form seen in Telmatherium. P' is either 

 slightly separated from the canine or placed im- 

 mediately behind it, according to the degree of 

 brachycephaly; in form it is either an extremely small, 

 rounded, bifanged tooth or considerably larger, with a 

 posterior internal cingulum in the higher stages. The 



Figure 267. — Lower jaws of 



, male and female 



Inferior view. One-fourth natural size. A, P. paludosus, Am. Mus. 11680, S 

 (neotype); Little Dry Creek, Bridger Basin, Wyo.; Bridger formation, middle 

 beds, level B 1. B, P. copeif, Am. Mus. 12206a, V; Henrys Fork, Lone Tree, 

 Bridger Basin; Bridger D 1 , 15 feet above white stratum. 



chief point to note in p^ is the strengthening and in- 

 creasing convexity of the tritocone or posterior outer 

 cusp (P. major). A very sharp distinction is seen in 

 the progressive transformation of p' and p* in Palaeo- 

 syops — namely, in the gradual development of a 

 mesostyle or median ridge separating the protocone 

 from the tritocone (P. leidyi), which appears to in- 

 dicate that in Palaeosyops the ectolophs of the premo- 

 lars are tending to become somewhat like those of the 

 molars, whereas in Manteoceras the ectolophs never 

 assume the molar form. The outer cusps of the 

 premolars of titanotheres never become crescentic 

 externally, however, and are thus essentially different 

 from those of the molars. 



In general, the grinding teeth are distinguished by 

 persistent brachyodont or short crowns, and the 

 persistence of the conules is undoubtedly correlated 

 with the persistent breadth of the grinders. 



