PHALANGEAL MORPHOLOGY OF PALEOCENE PLESIADAPIFORMES (MAMMALIA: ?PRIMATES): EVALUATION OF THE GLIDING HYPOTHESIS AND THE FIRST EVIDENCE FOR GRASPING IN A POSSIBLE PRIMATE ANCESTOR

It has been suggested that plesiadapiforms had phalangeal morphology indicative of mitten-gliding and thus were closely related to the extant flying lemur, Cynocephalus (Mammalia: Dermoptera). New plesiadapiform skeletons from middle Clarkforkian limestones in the Clarks Fork Basin, Wyoming, are the most complete known and have well documented dental associations. These new postcrania permit a more refined understanding of structure and positional behavior in Paleocene plesiadapiforms.

Morphological comparisons between a variety of extant primates and other mammals were made using multivariate analyses of phalangeal shape and bivariate analyses of phalangeal proportions. Results indicate that paromomyids differ from extant Cynocephalus in having manual intermediate phalanges shorter than those of the pes and manual intermediate phalanges lacking the elongation that is indicative of an interdigital patagium. These features suggest that paromomyids were not gliders like Cynocephalus. Instead, it appears that paromomyids were committed arborealists adapted for locomotion on large vertical supports, similar to extant claw-climbing callitrichids. In addition, pronounced flexor sheath ridges, curvature of proximal phalanges, and interphalangeal proportions of the pes indicate that hindlimb suspension may have been important during resting and feeding in paromomyids.

Morphological comparisons show that Carpolestes simpsoni was similar to other plesiadapoids in having intermediate phalanges with circular distal trochleae and mediolaterally compressed, dorsoventrally high distal phalanges II-IV. Carpolestes simpsoni differs from other plesiadapoids in having metatarsals and metacarpals of similar length; a divergent hallucial metatarsal with a weakly developed peroneal process; a short entocuneiform with a sellar joint for articulation with metatarsal I, and a dorsoventrally compressed, nail-like, distal hallucial phalanx. We infer that C. simpsoni was capable of grasping small diameter supports with both its hands and feet, in a manner similar to extant Petaurus and Tarsius.