EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



649 



length and slenderness, form of the great tuberosity 

 and supinator crest of the humerus and of the ole- 

 cranon. The manus has the deep carpus, relatively 

 long metacarpals, and extremely abbreviate ungual 

 phalanges of Amynodon; metacarpal III is enlarged, 

 the foot being functionally mesaxonic. 



UNASSOCIATED ASTRAGALI PBOVISIONALLY REFERRED TO 

 DOLICHORHINUS AND MESATIRHINUS 



The tarsus is known from unassociated specimens 

 only. The structure of the tarsus is uncertain. 

 Three types of relatively large astragali are found in 



Figure 582. — Left scapula 

 of Dolichorhinusf hyogna- 



Am. Mus. 1833; Uinta B 2. 

 sixth natural size. Compar 

 ure 590. 



One- 

 :Fig. 



Figure 583. — Humerus of 

 Dolichorhinus hyognaihus 



A, Am. Mus. 13164, Washakie B, 

 right humerus, front view; B, Am. 

 Mus. 1843, Uinta B 2, left humerus, 

 front (Bi) and distal (B2) views. 

 One-sixth natural size. 



the Eoiasileus-DolicJiorhinus zone (Washakie B 2 = 

 Uinta B 2). These are sketched in Figure 588. B 

 (Am. Mus. 1845) is said to be associated with part 

 of a Dolichorhinus skull. It differs from Mesatirhinus 

 in the short sustentacular facet, deeply grooved above; 

 also in the short neck. Of this type another astraga- 

 lus (Am. Mus. 1838, fig. 588, C) has a broader cuboidal 

 facet and is wider. A (Am. Mus. 2352, from Wash- 

 akie B 2), which is not associated with other remains, 

 agrees with Mesatirhinus in the long neck and long 

 sustentacular facet. D (Am. Mus. 1962), although not 

 associated with other remains, possibly belongs to Tel- 

 matherium. (See above.) If B belongs to Dolicho- 

 rhinus it is certainly distinctive. 



SKELETONS REFERRED TO DOLICHORHINUS LONGICEP8 



Three partial skeletons that have been referred to 

 this species are loiown. Two are in the Carnegie 

 Museum at Pittsburgh. They were discovered in 

 1912 by Peterson (1914.3) in the upper levels of horizon 

 B 1 of the Uinta Basin Eocene, on White River, Utah. 

 The skull, mandible, and hyoid bones of this specimen 



have been described in Chapter V; the vertebrae, 

 limbs, and feet, as described by Peterson," are noticed 

 below. The third skeleton referred to this species is 

 in the Field Museum at Chicago and was discovered 

 in 1910 by Riggs (1912.1) in the "upper Metarhinus 

 beds" (upper level of Metarhinus zone = Uinta B 1, 

 formerly included in Uinta A). A photograph (PI. 

 XXXII) and numerous measurements (see below) of 

 this skeleton were kindly supplied for this monograph 

 through the courtesy of Mr. Riggs. 



SKELETON OF DOLICHORHINUS LONGICEPS COMPARED WITH THAT 

 OF EOTITANOTHERIUM (DIPLACODON?) OSBORNI 



The description by Peterson (1914.1, pp. 132-137) 

 of the vertebrae and limbs of the specimen of Dolicho- 

 rhinus longiceps in the Carnegie Museum (No. 2865) 

 may be abstracted and restated as follows: 



The atlas. — In comparing the atlas with that of Eotitanothe- 

 rium osborni Peterson, it is at once observed that the bone is 

 proportionally higher and longer but of a less transverse di- 

 ameter, which is due chiefly to the shorter transverse process in 

 the present genus. The anterior cotyle is on the whole very 

 nearly as large as but is deeper than in Eotitanoiherium, and 

 its inferior surface is more distinctly separated. The odontoid 

 process of the axis is proportionally longer and reaches nearly 

 through the inferior arch of the atlas, while in Eotitanoiherium. 



Figure 585. — -Metatarsals 

 of Dolichorhinus hy o- 

 gnathus 

 Am. Mus. 13164; Washakie B. 

 Right metatarsals III and IV. 

 Ai, Front view; .Aa. proximal 

 view. One-third natural size. 



Figure 584. — Radius and ulna of 

 Dolichorhinus hyognathus 



Ai, Outer side view of proximal end of left 

 radius and ulna. Am. Mus. 13164, Wash- 

 akie B; A2, front view of same, combined 

 with distal end of radius. Am. Mus. 1831, 

 Uinta B 2; A3, rear view of left olecranon 

 shown in Ai. One-sixth natural size. 



it does not. The articulation for the axis is much deeper than 

 in Eotitanotherium and not nearly as broad, in this respect more 

 nearly suggesting the condition found in some Oligocene rhi- 

 noceroses {Diceratherium) than the horned titanotheres. The 

 transverse process is pierced by a large foramen, unlike Eoti- 

 tanoiherium, in which this canal is smaU, or completely absent. 

 The axis. — The body of the axis is possibly somewhat longer 

 than in Eotitanotherium, the anterior opening of the arterial 

 canal located farther back, and the postzygapophysis is smaller 

 and less rounded in outline, while the neural spine and the 

 ventral keel have approximately the same general proportions. 



" Peterson's final description of these skeletons (Carnegie Mus. Mem., vol. 9, 

 No. 4, 1924) was received too late for extended notice in this monograph. 



