656 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



immediately above the acetabulum, but there is a long 

 and rather slender neck of the Uium beyond which the 

 borders begin to expand. The acetabular border of 

 the ilium (a) presents a short, sharp curvature and is 

 relatively much shorter than in Palaeosyops. The 

 ischiac border (b) is much longer, with a gradual 



In Eotitanotherium oshorni the anteroposterior diameter of 

 the atlas is rather small, while transversely it is proportionally 

 greater than in the Oligocene forms. This is due in a great 

 measure to the longer transverse process of the Uinta form. 

 The cotyle for the occipital condyle is also deeper and the groove 

 for the odontoid process of the axis extends farther forward on 

 the inferior arch, due probably to the proportionally longer 

 odontoid in Eotitanotherium osborni. 



The axis of the type is represented by a portion of the centrum, 

 the complete neural arches, and the spinous process. The arch 

 is somewhat depressed by crushing, but it is evidently of rather 

 large size. The vertebra as a whole possibly has a smaller 

 anteroposterior diameter than is the case in most of the titano- 

 theres of the Oligocene; the articulating surface for the atlas is 



Figure 597. — Incomplete ilium and ischium of Diplacodon 

 elatiis 



Princeton Mus. 10393; Uinta C; provisionally described. After Scott and Osborn. 

 One-sixtli natural size. 



curvatme. It follows that the supra-iliac border 

 apparently presented outward more than directly 

 upward and forward. Below the acetabulum the 

 ischium has a triangular section, then expands in a 

 plane directly perpendicular to that of the ilium. 



Eotitanotherium Peterson 



Although the type specimens of Eotitanotherium 

 oshorni Peterson were found in the upper part of hori- 

 zon B 2 of the Uinta Basin, Utah, rather than in 

 horizon C (true Uinta formation), this animal is in a 

 stage of evolution in many respects similar to that of 

 the titanotheres of horizon C and therefore may be 

 conveniently described with them. 



Peterson's description of the skull and dentition 

 of the type and paratype and comparison with the 

 Princeton specimen of Diplacodon or ProtitanotTierium, 

 figured above, have been cited in Chapter V; his 

 description of the rest of the skeleton (1914.1, pp. 

 37-51), with modifications in the nomenclature, is as 

 follows : 



The atlas of the type (No. 2859) is quite complete. There is 

 also the greater portion of an atlas with the paratype (No. 

 2860). With regard to the posterior division of the arterial 

 canal it may be said that there appears to be some variation 

 in the Uinta species. Thus it is seen that in the type the base 

 of the transverse process is pierced by a small foramen (see fig. 

 598), while in the paratype there is no evidence of this foramen 

 on the posterior face of the transverse process. Of the later 

 Uinta forms there is apparently no atlas known. In comparing 

 the Oligocene titanotheres with the Uinta specimens before us, 

 there is a corresponding variation. The atlas of the Oligocene 

 types further varies in the anteroposterior diameter and in the 

 prominence of the neural spine and the transverse processes. 



FiGUBB 598. — Atlas and axis of Eotitanotherium oshorni 



Carnegie Mus. 2359 (type); Uinta B 2. Ai, Anterior view of atlas; As, posterior 

 view of atlas; Bi, posterior view of axis; Bj, lateral view of axis. One-third 

 natural size. 



located more laterally, and the postzygapophysis has a greater 

 vertical obliquity and a more nearly rounded outline than in 

 the latter. In the Princeton specimen <' it is seen that the 

 arterial canal is located back of the posterior edge of the articu- 

 lation for the atlas, while in Eotitanotherium osborni the fora- 

 men is, on a direct side view, partially hidden by the backwardly 



<i Scott, W. B., and Osborn, H. F., The Mammalia of the Uinta formation: 

 Am. Philos. See. Trans., vol. 16, pt. 3, p. 614, pi. 9, fig. 15, 1889. 



