EVOLUTION OF THE SKELETON OP EOCENE AND OLIGOCENE TITANOTHERES 



627 



and outward, whereas in D. 1 and in the succeeding 

 dorsals they face respectively upward and downward. 

 This oblique inward and outward facing of the pre- 



ih.inter-t/. 



FiGUBB 542. — Atlas of Palaeosrjops robiistus 



.■vm. Mus. 1580 Bridger formation, Bridger Basin, Wyo. Top view. One third 



natural size. 



zygapophysial and postzygapophysial facets, 

 respectively, is seen not only in Mnnteoceras, 

 Dolichorliinus, and the Oligocene forms but in 

 ungulates generally and is associated with the 

 vertical movement of the neck. 



In C. 5-C. 7 the posterior face of the cen- 

 trum approaches a transverse oval form, the 

 front face is wider at the top and narrow at the 

 bottom. Comparison with Manteoceras is shown 

 in Figure 552. 



The neural spines of the cervicals and dorsals 

 are narrow anteroposteriorly and deeply exca- 

 vated posteriorly. They increase rapidly in 

 height, from 55 millimeters in C. 4, 70 in C. 5, 

 and 135 in C. 7 to 201 in D. 1. The centrum 

 of C. 5 (posterior face) measures 43 millimeters verti- 

 cally, 55 transversely; that of C. 6 begins to assume 

 the narrower and deeper form characteristic of the 

 dorsals. The lamellae of C 4 and C. 5 are broadly 



The scapula of P. robustus is represented by a 

 referred specimen (Am. Mus. 1580). It is decidedly 

 wider in proportion to its height than the scapula 

 of Dolichorhinus. The humerus associated with the 

 skull (Am. Mus. 1580, fig. 546) exhibits a length of 

 345 millimeters (estimated). It is 

 thus slightly longer and much more 

 massive than the humerus of Palaeo- 

 syops? sp. (Am. Mus. 12205), from 

 Bridger D, and it is much longer than 

 the humerus of Manteoceras from 

 Bridger D (Am. Mus. 

 12204), which meas- 

 ures 260 millimeteis 

 The distal bieadth 



Figure 544. — Cervicals and dorsals of Palaeosyops robustus 

 Am. Mus. 1580; Bridger D (?). Cervicals 4-7, dorsals 1-3. One-third natural size. 



trochlea is 60 millimeters. The radius (fig. 546) is 

 extremely broad (71 mm.) both proximally and dis- 

 tally, a marked progressive character of the Palaeo- 

 syopinae. The ulna also sharply expands distally; 

 the olecranon rises to a 

 pointed rugose knob. 

 The associated carpus 

 agrees closely with that 

 of P. leidyi but is of 

 somewhat larger dimen- 

 sions. Mts IV measures 



FiG"0KE 543. — Atlas and axis of Palaeosyops leidyi? 

 Am. Mus. 12201. Bridger C 4. Inferior surface. One-third natural size. 



expanded downward, while those of C. 6 and C. 7 

 exhibit a transverse rodlike expansion, those of C. 6 

 measuring 134 millimeters transversely. These parts 

 are not very well preserved in the P. leidyi skeleton. 

 The disposition of the lamellae and of the spines 

 is different in details from that in the skeleton of 

 Dolichorhinus. 



115 millimeters; Mts III 

 expands to 49 distally. 

 Other characters of the 

 Palaeosyops rohustus 

 manus are as follows : The 

 most massive type, exhib- 

 iting graviportal and per- 

 haps aquatic adaptation; i-^-^fAT 

 brachypodal; carpus very Figure 545. — Left scapula of 

 broad (94 mm.) in upper Palaeosyops robustus 

 Bridger specimens, deep Am, mus. isso; Bridger c or d (?). 



, ± • 1 / A r, One-sixth natural size. 



anteroposteriorly (40 » 



mm.), measuring vertically from summit of lunar to 

 bottom of magnum 50 millimeters; metacarpals robust, 

 shafts widely spreading distally ; scaphoid very deep 

 anteroposteriorly and laterally (thus differing from 



