EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



637 



neck was relatively shorter, the head more elongate, 

 thus bringing the lips closer to the ground. 



Yet, as compared with the other middle Eocene 

 titanotheres, MesatirJiinus is mediportal, and all parts 

 of the skeleton which are known are relatively narrow 

 and deep in their proportions, including the atlas, the 



Mesatirhinus petersoni, Princeton Mus. 10013, Figures 563, 565, 



566; Bridger D. 

 Mesatirhinus petersoni?, Am. Mus. 11659 (fore and hind limbs 



not associated). Figure 564; Bridger C 5. 

 Mesatirhinus petersoni, Am. Mus. 1571; Wasliakie A. 

 Mesatirhinus megarhinus, Am. Mus. 1523 (associated), Bridger 



C? 



■■^■'^"U"i n f'"! n r 





Hind limbs // ::^y"' li 



A.M. 11659 ^""^ yj^ fy 



I'iGURB 558. — Restoration of the skeleton of Mesatirhinus petersoni 

 A provisional reconstruction of this light-limbed titanothere of Bridger D, based on specimens in the American Museum pertaining to various 

 individuals. The backbone, scapula, and pelvis are restored in broken lines from BolichoThinus: the ribs from Palaeosyops. One-twelfth 

 natural size. 



imbs, the carpals and tarsals, and the metapodials. 

 We observe at once (figs. 512, 520) that the digits of the 

 manus are more compressed laterally and at the same 

 time more paraxonic and tetradactylous — that is, the 

 fifth digit of the manus is relatively longer than in the 

 above-described Palaeosyops and LimnoTiyops. 



The above individuals include only a single vertebra, 

 the atlas. The scapula and pelvis are still unknown. 

 When found they will furnish us with very significant 

 characters. 



In the following description of the skeleton it seems 

 best to describe together the parts belonging to the 



Figure 559. — Restorations of Mesatirhinus petersoni (left) and Palaeosyops leidyi (right) 

 By Mrs. B. M. Fulda. Bridger C and D. About one-thirtieth natural size. 



The above diagnosis is important because this type 

 of skeleton is broadly ancestral to the mediportal and 

 brachypodal DolichorJiinus. 



The skeletal material of MesatirJiinus, like that of 

 Manteoceras, is rarely associated with parts of the 

 skull or teeth, so that identifications are difficult; 

 parts only of two skeletons have been found asso- 

 ciated. The specimens listed below have been col- 

 lected. 



different species of Mesatirhinus. The geologically 

 oldest specimen named in the above table is M. mega- 

 rhinus, from the Bridger formation, level unknown 

 (Am. Mus. 1523), consisting of a skull with incomplete 

 axis. From Spanish John's Meadows, Bridger Basin, 

 Wyo. (level Bridger C or D), came the very well- 

 preserved radius, ulna, and manus (Princeton Mus. 

 10013) that were describedand figured by Earle (1897.1, 

 pp. 358-364) as belonging to Limnohyops laticeps. 



