EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



Summary of contrasting cliaracters of the carpus and manus in middle Eocene titanotheres 



607 



Palaeosyopine group. 



Manteoceras-Dolichorhinus group 



Typical genera, Palaeosyops (subgraviportal), Limnohyops (mediportal) 



Typical genera, Mesatirhinus (mediportal), Manteoceras, Dolichorhinus (sub- 

 graviportai) 



1. Carpus broad, composed of relatively broad, low, and deep 



(anteroposteriorly) elements, correlated with broader 

 spreading digits and spreading or rounded hoofs. 



2. Scaphoid broad, deep anteroposteriorly, outer lateral face 



prolonged backward, radial facet rounded. 



3. Cuneiform (Palaeosyops) broad, chief diameter horizontal. 



4. Trapezium large, articulating with trapezoid, with Mtc II, 



but not generally with the scaphoid. 



5. Trapezoid relatively large, subquadrate in form in front view. 



6. Magnum large, with five to six facets, hook of magnum 



strongly asymmetrical, pointed. 



7. Unciform more horizontal. 



8. Metacarpals miore mesaxonic — that is, Mtc III relatively 



elongate; Mtc V abbreviate. 



9. Metacarpals with deep proximal facets for the carpals at the 



extremities. 



10. End phalanges rounded or spreading at the extremities. 



1. Carpus composed of relatively -high elements, less deep 



anteroposteriorly, hoofs truncate and spreading dlstally. 



2. Scaphoid relatively high, more shallow anteroposteriorly, 



radial facet flat. 

 2a. Lunar high and laterally compressed, resting chiefl.v on 

 unciform. 



3. Cuneiform relatively high and laterally compressed. 



4. Trapezium large and deep vertically, articulating with 



trapezoid, with Mtc II, also with scaphoid (Mesatirhinus) . 



5. Trapezoid relatively small. 



6. Magnum high, relatively narrow, subquadrate, with five 



facets, hook of magnum more symmetrical. 



7. Unciform more oblique. 



8. Metacarpals more paraxonio — that is, Mtc V well devel- 



oped and podium more tetradactyl. 



9. Metacarpals with proximal facets for carpals truncated 



rather than deep, with distal facets less globose. 



10. End phalanges broadly expanded distally. 



The pelvis of the middle and later Eocene titano- 

 theres has passed beyond the mediportal Tapirus 

 stage and is in a stage between the subgraviportal 

 and graviportal, conforming with the principles of 

 the evolution of the pelvis set forth in Chapter IX 

 (pp. 743-745). Although associated and complete 

 pelves are rare, the material available throws a great 

 deal of light on the characteristic form and develop- 

 ment of this important organ. 



The chief materials and the geologic horizons at 

 which they were collected are as follows: 



Eotitanops horealis, Am. Mus. 14887 (fig. 501): Wind River 



A or B. 

 Limnohyops laticeps, Yale Mus. 11000 (fig. 532) : Bridger C or D. 

 Limnohyops ? sp., Am. Mus. 2348 ' (fig. 538) : Washakie A. 

 Palaeosyops frobustus, Princeton Mus. 10232 (fig. 539) : Bridger 



Cor D. 

 Palaeosyops fmajor, Am. Mus. 13116 (fig. 533): Bridger B. 

 f Manteoceras manteoceras, Am. Mus. 2358 (fig. 555) : Washakie 



B. 

 Dolichorhinus hyognathus, Am. Mus. 1843 (figs. 579, 580): 



Uinta B. 

 f Dolichorhinus ?hyognathus, Am. Mus. 1860: Uinta B. 



Of the above the pelvis of Eotitanops (fig. 501) 

 shows a mingling of subcursorial and prophetic medi- 

 portal characters. The complete associated pelvis of 

 the type of Limnohyops laticeps in the Yale collection 

 belongs to a juvenile individual, which may partly 

 explain the fact that it is in a more primitive stage of 

 development than any other middle Eocene titano- 



' Specimen mounted with skeleton of P. leidyi in American Museum. 

 101959— 29— VOL 1 42 



there pelvis known; the superior border of the iliac 

 crest is partly thin and concave, representing the 

 crista iliaca between the rugose borders of the tuber 

 sacrale and tuber coxae. 



A similar pelvis in a somewhat more advanced 

 stage (fig. 538) is that from Washakie A (Am. Mus. 

 2348), which has been mounted with the skeleton of 

 Palaeosyops leidyi in the American Museum. This 

 represents a slightly more advanced stage, which 

 nevertheless retains the thin, slightly concave crista 

 iliaca between the rugose areas of the tuber coxae and 

 tuber sacrale. 



A pelvis certainly belonging to Palaeosyops, from 

 Bridger B (Am. Mus. 13116, fig. 533), is distinguished 

 by the elongate os innominatum and by the uniformly 

 convex superior crest of the ilium. 



Of this type also is the pelvis (fig. 539) in the Prince- 

 ton Museum (No. 10232), attributable to P. leidyi or 

 P. rohustus, distinguished by a much broader ilium, 

 with a uniformly convex superior border. 



Referable to Manteoceras is the finely preserved 

 pelvis (Am. Mus. 2358) from Washakie A or B, 

 characterized by very great iliac breadth (fig. 555) 

 and the broad expansion of the supra-iliac border. 

 This is an advanced subgraviportal type, prophetic 

 of the form of the pelvis in the Oligocene titanotheres. 



The pelvis associated with Dolichor'hinus hyognathus 

 from Uinta B (Am. Mus. 1843) is again elongate 

 (fig. 580), with a uniformly convex superior border 

 of the ilium. 



The comparative measurements of these pelves are 

 shown in the accompanying table. 



