EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



309 



meters transversely as compared with 99 in L. mono- 

 conus. The width of the occiput across the top is 

 108 millimeters. At the sides of the exoccipital por- 

 tion are indistinctly seen the mastoid foramina. Just 



Figure 261. — Skulls of three species of Limnohyops 



Occipital view. One-fourth natural size. A, L. monocomis, Am. Mus. 11679 

 (type); Grizzly Buttcs, west Bridger Basin, Wyo.; Bridger formation, level B 2. 

 B, L. laticeps, Yale jMus. 11000 (type, vertically crushed); Bridger Basin; upper? 

 Bridger. C, L. matlhewi, Am. Mus. 11684 (type); Grizzly Buttes, west Bridger 

 Basin; Bridger formation, level B 2. 



above the foramen magnum are very faintly indi- 

 cated the pair of facets characteristic of this genus, 

 more distinctly marked in Telmatherium. 



Limnohyops monoconus Osborn 



Plate LXII; te.xt figures 117, 261-263, 484, 485, 510-514, 516, 

 519-523, 525, 527-530, 685, 686, 701, 723 



[For original description and type reference see p. 130. For skeletal characters see 

 pp. 604, 612] 



Type locality and geologic Tiorizon. — Grizzly Buttes 

 (west), Bridger Basin, Wyo.; Bridger formation, Pal- 

 aeosyops paludosus-Orohippus zone, level B 2. This 



specimen was discovered by the American Museum 

 expedition of 1903. It was on the level of L. laevidens 

 and L. matthewi and thus belongs to a much lower 

 horizon than L. laticeps. This specimen may rep- 

 resent, however, the geologic intrusion of a fauna from 

 a higher level, and it is therefore quite possible that it 

 was not contemporaneous with L. laevidens. The 

 presence of these specialized forms, L. mattheivi and 



Figure 262. — Skull of Limnohyops matthewi 



One-fourth natural size. Am. Mus. 11684 (type) ; Grizzly Buttes (west) , Bridger 

 Basin, Wyo.; Bridger formation, level B 2. Ai, Side view; As, basal view. 



L. monoconus, on the same geologic level as the 

 primitive forms L. laevidens and L. priscus is contrary 

 to the general law of succession observed among 

 other forms in the Bridger Basin. It may indicate 

 either some source of error in the geologic records 

 or some deviation from the generally horizontal dis- 

 tribution of the Bridger titanotheres. Another ex- 

 planation is possible: that Limnohyops was evolving 

 more rapidly in other geographic centers, from which 

 these progressive forms may have migrated. 



Specific characters. — M^ without hypocone, roundly 

 triangular in form, with broadly extended ectoloph 

 and parastyle. P*-m', 142 millimeters; p'-m^, 156. 

 Condyle to incisive border 439 millimeters (estimated); 



