EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



667 



Comparative measurements of cervicals, dorsals, and lumbars, in 

 millimeters " 



C. 1 (atlas) 

 C. 2 (axis) . 



C. 3 



C. 4 



C. 5 



C. 6 



C. 7 



D. 1 



D. 2 



D. 3 



D. 4 



D. 5 



D. 6 



D. 7 _. 



D. 8 



D.9= 



D. 10 



D. 11 



D. 12 



D. 13 



D. 14 



D. 15 



D. 16 



D. 17 



L. 1 



L. 2 



107 



112 



106 



111 



113 



114 

 "118 



117 



113 



100 + 



109 



103 



103 



''107 



90 



«81 

 84 



• The longitudinal measurements are taken along the inferior line of the centra 

 from between the edges of the articular facets; the vertical and transverse measure- 

 ments are taken on the anterior faces of the centra. 



<> Height of spine, 695 millimeters. 



•= The position of this vertebra in the series is somewhat doubtful. 



' Estimated. 



• Crushed. 



Dorsals. — There are 17 rib-bearing or dorsal verte- 

 brae. The first dorsal (D. 1) marks a very abrupt 

 transition from the cervicals by the sudden elevation 

 of its very broad spine to a height of 590 + millimeters; 

 the laterally flattened upper portion of the spine rests 

 upon the relatively short triangular lower portion. 

 In the succeeding dorsals, D. 2-D. 10 (PI. CXCIX), 

 the triangular basal portion of the spine, deeply exca- 

 vated posteriorly (fig. 4), becomes relatively higher 

 until in D. 7 it extends nearly to the top of the 

 spine. The spine of D. 2 (PI. CXCVIII) appears 

 to have been the stoutest and the most elevated ; it is 

 more backwardly directed than that of D. 1. From 

 D. 3 to D. 17, inclusive, the spines gradually diminish 

 in height and become more slender and more back- 

 wardly directed. In L. 2 (PI. CC) the spine is short 

 and obliquely directed backward. 



The zygapophyses are characteristic: the post- 

 zygapophysis of D. 1 and prezygapophysis of D. 2 

 are transversely oblique or face respectively outward 

 and inward, whereas in the American Museum 

 skeleton referred to Brontops they are subhorizontal. 

 The postzygapophyses of D. 2 face directly down- 

 ward and backward — that is, in a more nearly hori- 



zontal plane. Similarly, the postzygapophysis of D. 2 

 and the prezygapophyses of D. 3-D. 15 are antero- 

 posteriorly oblique or subhorizontal, facing downward 

 and upward respectively rather than outward and 

 inward. In D. 14 a transition occurs to the outward 

 facing of the postzygapophyses and the inward facing 

 of the prezygapophyses. In D. 17 the articulation 

 is very slightly revolute, convexo-concave. In L. 1 

 the articulation is not preserved; in L. 2 (PL CC) 

 the postzygapophyses are flat and face obliquely 

 outward and downward. 



Rib jacets. — Throughout the series the capitular 

 facets are the largest on the posterior sides of the 

 centra, attaining a very great size, for the especially 

 large third, fourth, and fifth ribs. In D. 12-D. 17 

 the capitular facets rise from the base of the neural 

 arches, and even in the posterior dorsals, D. 15-D. 17, 

 the tubercular facets are relatively large and well 

 developed. 



Lumbars. — The lumbars are imperfectly preserved, 

 one of these vertebrae being lost entirely. The lum- 

 bar exhibits the following distinctive characters: Spine 

 recumbent, zygapophysis facing obliquely outward and 

 inward, not revolute, transverse processes rather feeble, 

 with broadly rugose and sessile inferior keel. 



Sacrals. — There are four sacrals (Pis. CCXVIII, 

 CCXIX) rather imperfectly preserved; they rapidly 

 diminish in size, S. 1 being very much larger than the 

 succeeding sacrals. 



Oaudals. — An unusually perfect series of 16 caudals 

 (PI. CCI) is preserved in sequence behind the last 

 sacral. The relatively small size of the most anterior 

 caudal (figs. 1-3) is correlated with the small size of 

 the posterior sacral and a small tail. The centra 

 increase in length from C. 1, which measures 43 

 millimeters, to C. 9, which measures 70, and dimin- 

 ish to C. 16, which measures but 35. Neural spines 

 and rapidly diminishing zygapophyses were present 

 on C. 1-C. 8. C. 3 (figs. 6, 7, 8) exhibits a chevron 

 inclosing the haemal artery; this element may also 

 be preserved in C. 4 (figs. 9, 10) and C. 5 (figs. 11, 12, 

 13). The transverse processes rapidly diminish behind 

 C. 1 and finally disappear in C. 11. The centra are 

 biconvex. Beginning at C. 8 the centra become 

 laterally compressed, and the posterior centra, C. 12- 

 C. 16, are decidedly compressed laterally. 



i?i6s.— Nine perfect ribs (Pis. CCII, CCIII) are 

 preserved and fragments of others. On the whole they 

 are more slender and rounded in section than in the 

 skeleton of Brontops in the American Museum, de- 

 scribed below. 



Sternebrae. — Three of the midsternebrae are pre- 

 served, measuring collectively 290 millimeters; the 

 anterior (restored in PI. CCXXIX) and one or more pos- 

 terior sternebrae are missing. The supposed second 

 sternebra is broadly depressed in section, measuring 

 but 42 millimeters vertically, 123 anteroposteriorly, 



