EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



629 



that of the manteoceratine group); lunar deep antero- 

 posteriorly and broad laterally, resting broadly on 

 magnum as well as on unciform; trapezium small, 

 broadly articulating with trapezoid, and barely articu- 

 lating with Mtc II, no 

 facet apparent for scaph- 

 oid; trapezoid broad; 

 magnum very broad, 

 with six distinct faceted 

 angles ; large lunar facet 

 Figure 547. — Left astragalus of appearing in front view, 

 Palaeosyops copei? hook of magnum asym- 



Am. Mus. 12205a; Bridger D 1; front (Ai) and metrical, pointed ; Unci- 

 rear (A2) views. One-third natural size. !■„„,„ u „J^„ ■U„^4 



form broadly hori- 

 zontal, supporting more than half of the lunar; ter- 

 minal phalanges cleft and somewhat rounded rather 

 than spreading distally; the carpus while not ancestral 

 is in general analogous to that of the heavy Oligocene 

 titanotheres, namely, Megacerops and Bronfotherium. 



Figure 548. — Fore limb of Palaeosyops copei? 



Am. Mus. 12205; Bridger D 1. Ai, Front view of left fore arm and manus, one-sixth 

 natural size; A2, outer view of same, with humerus, one-sixth natural size; A3, right 

 ungual phalanx of median digit, inferior view, one-sixth natural size. 



Palaeosyops copei 



Two skeletons found close together on level D 1 of 

 the Bridger Basin (Am. Mus. 12205 and 12205a) are 

 especially valuable because they give us the propor- 



tions of the limbs and the complete structure of the 

 manus of an exceptionally short-footed type of Palaeo- 

 syops, the specific determination of which is doubtful; 

 it may be provisionally referred to P. copei. One of 

 these specimens (No. 12205a) belongs to a younger 

 and smaller individual, the other (No. 12205) to an 

 older and larger individual. 



Skull and skeleton of the younger and smaller individual (No. 12205n) 



Slcull. — The skull belongs to a rather young indi- 

 vidual. It exhibits the following especially important 

 characters (fig. 281): (1) The nasals taper slightly 

 anteriorly, much less so than in Palaeosyops leidyi; 

 (2) the nasals are not deeply decurved at the sides as in 

 LimnoTiyops; (3) the nasals exhibit V-shaped prolonga- 

 tions on the sides of the face as in Palaeosyops; (4) there 



Figure 549. — Left manus of Palaeosyops copeif 



Am. Mus. 12205; Bridger D 1. Ai, Front view of manus; A2, upper view of 

 phalanges of median digit; A3, inner side view of carpus; Ai, upper or proximal 

 view of carpus. One-third natural size. 



are very slight and smooth prominences on the sides of 

 the face at the junction of the nasals and frontals, occu- 

 pying the same position as the rudimentary horns which 

 have been observed in Palaeosyops; (5) there is a 

 narrow and apparently deep sagittal crest. 



Fore limb. — The chief upper limb character is that 

 the humerus is longer (335 mm., estimated) than the 

 radius (223 mm.), indicating slow speed, and we are 

 surprised to find that the manus is shorter than in 

 either Palaeosyops leidyi or P. roiustus. The humerus 

 measures about 63 millimeters across the distal 

 trochlea. The ulna and radius are much less massive 

 than in the type of Palaeosyops leidyi and slightly less 



