EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



661 



Measurements of No. S860 



Millimeters 



Scaphoid, vertical diameter 35 



Scaphoid, transverse diameter 33 



Scaphoid, anteroposterior diameter 53 



Pisiform, total length 60 



Trapezoid, vertical diameter 20 



Trapezoid, transverse diameter 26 



Trapezoid, anteroposterior diameter 36 



Mtc II, greatest length 153 



Mtc II, transverse diameter of head, approximate 37 



Mtc II, transverse diameter of middle of shaft, approxi- 

 mate 30 



Mtc II, transverse diameter of near distal end, approxi- 

 mate 42 



Mtc V, greatest length 125 



Mtc V, greatest transverse diameter of head 36 



Mtc V, greatest transverse diameter of middle of shaft 20 



Mtc V, greatest transverse diameter of near distal end 33 



Proximal phalanx, length 31 



Proximal phalanx, transverse diameter of proximal end 29 



Proximal phalanx, transverse diameter of distal end 26 



The pelvis of No. 2859 is represented by the greater portion 

 of the ilium. It is quite broad across the gluteal surface, but 

 the point of the iUum probably did not project laterally as 

 much as in B. validus. The constricted portion of the neck is 

 actually longer than in the latter species and also longer than 

 in the Princeton specimen of Diplacodon as represented on 

 Plate VIII in Scott and Osborn's worli. The pelvis as a whole 

 was consequently proportionally longer and probably narrower 

 than in the Oligocene genus. The ischium and pubis are not 

 represented. 



In No. 2860 the lower half of the femur is present. The tibial 

 and dorsal faces of the shaft are convex, while posteriorly it 

 presents a flat surface. On the fibular angle may be seen the 

 lower portion of the prominent ridge below the third trochanter, 

 which decreases in prominence in its downward course. Near 

 the distal end the fibular border presents a roughened area for 

 muscular attachment, back and below which is the rather shallow 

 supracondylar fossa. Distally the condyles are rather well 

 separated by the deep and broad intercondylar fossa. The 

 lateral sides of the distal end (especially the fibular) is well 

 marked by the rugose attachment for muscles. The rotular 

 trochlea is proportionally deeper and narrower than in Menodus, 

 and the fossa immediately above it is much deeper and better 

 defined. In this respect the present genus agrees better with 

 Figure 5 on Plate VIII of Scott and Osborn's publication. 



Measure7nents of femur of No. 2S80 



Millimeters 



Total length of the fragment 280 



Transverse diameter of shaft about the middle region of the 



fragment 60 



Transverse diameter of distal end 108 



Anteroposterior diameter of distal end 110 



The greater part of the tibia is represented in the paratype 

 No. 2860, but it is badly crushed. Another individual, No. 2862, 

 has both tibiae present and is approximately of the same size 

 as the individuals we are describing. The bone is very nearly 

 as long as in B. validus. The ends are not expanded as in the 

 latter form, while the shaft is flatter, due in part to crushing. 

 The superior end carries a heavy and bifid spine, while the 

 upper anterior extremity displays the broad groove for the 

 patellar ligament as in Menodus. The cnemial crest, though 

 prominent, does not descend low on the shaft, another feature 

 recalling what may be observed in B. validus and in the Uinta 

 specimen figured by Scott and Osborn.''^ The anterior border 



*2 If the illustratioa on PI. VIII, Fig. 6, in Scott and Osborn's publication is 

 one-fifth of nature, as is that of the femur in the same plate, the tibia of that form is 

 actually shorter than that in the genus here described. 



of the distal trochlea was found weathered off, but the posterior 

 surface is complete and presents a very prominent descending 

 process on the median ridge of the articulating trochlea very 

 similar to what is seen in the later Uinta form and in Menodus. 

 From the material in hand it is shown that the hind hmb of 

 Eolitanotherium osborni corresponds well in length with the 

 fore limb. 



Measurements of tibia of No. 2862 



Millimeters 



Greatest length, approximate 415 



Transverse diameter of head 100 



Transverse diameter of shaft, middle region 48 



Transverse diameter of distal end, approximate 75 



The hind foot of No. 2860 is represented by the calcaneum, 

 the astragalus, and the second and fourth metatarsals. 



When compared with the Princeton specimen from a higher 

 Uinta level and also with the Oligocene genera, the tuber of the 

 calcaneum in the present form is seen to be as long in proportion 

 and compressed laterally to the same extent, while that portion 

 carrying the sustentacular facets is longer. The fibula also 

 ■ apparently articulates with the calcaneum, but the posterior 

 portion of the tibial trochlea did not touch the calcaneum as in 

 Diplacodon and in Menodus. The astragalus is higlier and 

 narrower, and the metatarsals are longer and much slenderer 

 than in the latter genera. 



When compared in more detail there are a number of differ- 

 ences between the genera here compared. On the calcaneum 

 of the genus under description the proximal astragalar facet 

 is not raised as high above the surface as in Menodus. The 

 greater process of the distal end extends lower down and the 

 facet for the cuboid is more oblique than in Menodus. As 

 already stated, the astragalus is higher and narrower, the 

 trochlear groove is deeper, with the articular surfaces of the 

 two condyles steeper, and the neck separating the distal end 

 from the trochlea longer than in the astragalus of the Oligocene 

 form and also somewhat longer than in Diplacodon as figured 

 by Scott and Osborn. Furthermore, the distal end of the 

 astragalus of the present form is more unequally divided by the 

 navicular and cuboid facets than in the Oligocene genus. These 

 facets of the astragalus in Menodus are more nearly subequal in 

 size, the cuboid facet having increased in size as well as being 

 located more distally on the bone, while in Eotitanotherium 

 this facet occupies a comparatively narrow area on the fibular 

 angle and is placed laterally. 



The most noticeable difference of the astragalus of Eotitano- 

 therium osborni and that of the Princeton specimen as figured 

 (PI. VIII, fig. 86) seems to be in the three distinct astragalar 

 facets (viz, ectal, sustentacular, and cuboidal) of the latter, 

 while in the present form the ectal, besides extending higher, 

 unites with the cuboidal facet without distinct separation, 

 the two forming a perfect right angle apparently similar to 

 that in Mesatirhinus.*^ 



Aside from the greater proportionate length the metatarsals 

 differ from those in Menodus by being arched forward to a 

 greater degree. The shaft of Mts IV is more cylindrical, 

 and the facet for the cuboid more oblique. 



Measurements of No. 2860 



Astragalus: Millimeters 



Total length 71 



From lower end of external condyle to distal end 26 



Greatest transverse diameter 68 



Transverse diameter of trochlea 56 



Calcaneum: 



Greatest length 124 



Length of tuber 64 



Vertical diameter of tuber 45 



Transverse diameter of tuber 22 



Transverse diameter at sustentaculum 70 



<3 Osborn, H. F., Am. Mus. Nat. Hist. Bull., vol. 24, p. 68, 1908. 



