756 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



than its depression as seen in other graviportal types) ; 



(2) lowering of the lateral rugosity of the great tro- 

 chanter to unite with that of the third trochanter; 



(3) depression and lowering of the third trochanter 

 from the upper to the middle portion of the shaft 

 (paralleling Astrapofherium and differing from the 

 typical rectigrades, such as Mastodon, in which the 



noteworthy in Manteoceras and extreme in Bron- 

 totherium.; (6) straightening, flattening, and elongation 

 of the shaft of the femur to parallel the graviportal 

 rectigrade type (Elephas) far more closely than the 

 graviportal digitigrade type of the rhinoceroses. 

 Both the syngenetic and teleogenetic characters of the 



A B C D E F G 



Figure 686. — Limb structure of perissodactjds: Hind limbs of Eocene and Oligocene titanotheres belonging to 



several phyla 



These limb segments (proximal elements above, distal below) show the range of adaptation, which includes subcursorial or primitive mediportal 

 (A), mediportal (B-F), and graviportal (G) types. A, Eoiiianops princeps: B, MesatirJiinus petersoni; C, Palaeosyops major; D, Limnohyops 

 monoconus: E, Manteoceras vianteoceTas: F, DoUchorhinus hyognathus; G, Brontops robustus. A-F, one-ninth natural size; G, one-fourteenth 

 natural size. Scales approximate. 



second and third trochanters become sessile); (4) low- 

 ering of the second trochanter toward the middle por- 

 tion of the shaft (thus differing from other graviportal 

 digitigrades, such as Rhinoceros, in which the second 

 trochanter remains high up on the shaft); (5) great 

 elongation of the femur and abbreviation of the tibia. 



femur are seen to be quite distinct from those of other 

 graviportal perissodactyls and are very distinctive 

 throughout the series. The only analogy with mem- 

 bers of other families is seen in the comparison of the 

 hind limb of MesatirJiinus and Tapirus terrestris, but 

 this is not very close. 



