EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



631 



Palaeosyops copei? 



From an uncertain level in the Washakie Basin 

 comes an imperfect pes (Am. Mus. 5097) associated 

 with other limb fragments, which Cope erroneously 

 referred to his "Palaeosyops vallidens" but which is 

 certainly a member of the Palaeosyopinae, whereas 

 Cope's P. vallidens is now referred to LclidiorJiinus 

 vallidens, a member of the ilanteoceras-BolicJiorhinus 

 group. Possibly this pes is referable to P. cojpei. 



The astragalus in question agrees in most characters 

 with those referred above to Palaeosyops copei (Am. 

 Mus. 12205, 12205a) but is distinguished by the 

 wider sustentacular facet, deeper navicular facet, and 

 lower internal trochlear keel. The broad cuboidal 

 facet also rounds off into the distal calcaneal facet; 

 the pit on the inner face of the astragalus, below the 

 internal trochlear keel, is very deep, and the internal 

 distal protuberance for the lateral ligament is also 

 very prominent; the depression for the tip of the 

 fibula is wanting. The cuboid (absent) was elongate, 

 and Mts IV does not articulate with the ectocuneiforra 

 (cf. P. leidyi, above). 



Another palaeosyopine Washakie specimen from 

 the Cope collection (Am. Mus. 5105) is an astragalus 

 associated with fragmentary limb bones and bearing 

 the same museum number as the upper dentition which 

 was referred to above as allied to Palaeosyops copei. 

 The characters of the astragalus do not support this 

 association; it is about one-fourth smaller than that of 

 P. leidyi and has a relatively narrower neck and 

 narrower ectal and sustentacular facets, the ectal 

 facet being shallow. It rather resembles a small 

 Limnoliyops. 



SUBFAMILY MANTEOCERATINAE 



Graviportal titanotheres of the upper deposits of 

 the Bridger Basin, Wyo., the lower deposits of the 

 Washakie Basin, Wyo., and the upper deposits of the 

 Uinta Basin, Utah. Feet brachypodal. Ungual pha- 

 langes truncate. Tibia very short. Astragalus wide. 

 Manteoceras 



General features. — Judging from its limb proportions, 

 M. manteoceras was a slow-moving animal, much less 

 alert than the tapir (T. terrestris) and less swift than 

 its congeners of Mesatirhinus. All its known skeletal 

 parts were found in Bridger D, so that it was con- 

 temporaneous with the larger and more massive species 

 of Palaeosyops. These parts tend to confirm the view 

 that Manteoceras was allied to Mesatirhinus , DolicJio- 

 rhinus, and the Oligocene titanotheres. The Manteo- 

 ceras of this period was a short, low-bodied animal. 

 The skeleton, like the skull, is in many features 

 prophetic of the Oligocene titanotheres; it is more 

 paraxonic and tetradactylous, D. 5 being relatively 

 longer than in Palaeosyops; the tibiae are relatively 

 shorter (x%^ of the femur) than in any other Eocene 

 titanothere; the humerus is intermediate in length and 



in its tuberosities foreshadows that of Oligocene type, 

 there are broad flangelike pleurapophyses in the 

 posterior cervicals. Many of the adaptive analogies 

 ally it to Palaeosyops, although the deeper paleotelic 

 resemblances ally it to Dolichorhinus. 



Generic characters. — Atlas narrower than in Palaeo- 

 syops but broader than in Mesatirhinus; axis with a 

 high spine; neural canal of cervicals and anterior 

 dorsals rounded rather than angulate superiorly; 

 anterior faces of cervical centra subcircular, lateral 

 flange on C. 6 large, spines of cervical and dorsal ver- 

 tebrae abbreviate as in Palaeosyops, second dorsal 

 with prezygapophysis forming an angle with the neural 

 spine. Humerus intermediate to short; manus mesa- 

 tipodal; superior facets of carpals and metacarpals 

 flatter, relatively wider posteriorly; scaphoid shallower 

 anteroposteriorly; lunar with subvertical magnum 

 facet; cuneiform flatter; trapezoid with facet for trape- 

 zium continuous with scaphoid facet. Magnum rela- 

 tively narrow, with scaphoid facet subvertical, pos- 

 terior hook spatulate; unciform relatively narrow, 

 with subquadrate lunar facet. Metacarpals longer, 

 narrower and more straight-sided than in Palaeosyops, 

 but broader than in Mesatirhinus; proximal facets 

 wide posteriorly; metacarpal V relatively longer than 

 in Palaeosyops; phalanges smaller, shorter, and 

 broader; distal phalanges broadly expanded, truncate, 

 and deeply cleft. Femur of intermediate length. 

 Tibia both relatively and absolutely short, with broad 

 proximal end. Astragalus intermediate, rather broad, 

 with broader convex tibial keel of the trochlea and 

 broad cuboid facet, but also with straight-sided sus- 

 tentacular facet and deep navicular facet. 



Materials. — Material referable to this genus is rare. 

 There are, in fact, only two specimens in which parts 

 of the postcranial skeleton are certainly associated 

 with the skull and dentition — Am. Mus. 1587, a young 

 adult male from Bridger D, the skull of which is shown 

 in Figure 303, and Am. Mus. 12204, a crushed skuU of 

 an old animal, possibly a female, from Bridger D 1 

 or D 2. A third specimen (Am. Mus. 12216), con- 

 sisting of an incomplete manus, is not associated with 

 a skull or with dentition but agrees so closely with 

 Am. Mus. 1587 that it may be referred with confi- 

 dence to Manteoceras. 



From these three specimens we learn the principal 

 characters of the cervical vertebrae, anterior dorsals, 

 humerus, manus, femur, tibia, and astragalus. A 

 pelvis is provisionally referred. The remaining verte- 

 brae, ribs, sternals, and most of the pes are practically 

 or wholly unknown. 



Manteoceras manteoceras 



A close examination of the vertebrae of Manteo- 

 ceras in comparison with those of Palaeosyops and 

 Dolichorhinus shows that the differences relate mostly 

 to rather minor details and do not lend themselves 

 to broad characterizations. It may be said, how- 



