Phalangeal morphology of the paromomyidae (?Primates, plesiadapiformes): The evidence for gliding behavior reconsidered

A comparative morphometric analysis of isolated proximal and intermediate p halanges attributed to the paromomyids Ignacius graybullianus and Phenacole mur simonsi was undertaken to test the hypothesis that these fossil phalang es exhibit evidence of a dermopteran-like interdigital patagium, Linear dim ensions were collected for the fossil phalanges and a comparative sample of associated proximal and intermediate phalanges representing extant tree sq uirrels, tree shrews, dermopterans (colugos), gliding rodents and marsupial s, and prosimian primates. Quantitative data indicate that the proximal and intermediate phalanges of paromomyids are most similar in their overall sh ape to those of the dermopteran Cynocephalus. The proximal phalanges of par omomyids and colugos possess well-developed flexor sheath ridges and broad, high shafts, whereas the intermediate phalanges of these taxa are most sim ilar to one another in their trochlear morphology. Discriminant analysis in dicates that all of the paromomyid intermediate phalanges resemble those fr om colugo toes more so than those from colugo fingers. Moreover, the relati ve length and midshaft proportions of both the proximal and intermediate ph alanges of paromomyids closely resemble those of several squirrels that lac k an interdigital patagium. The following conclusions are drawn from this s tudy: 1) paromomyids share a number of derived phalangeal features with mod ern dermopterans that may be indicative of a phylogenetic relationship betw een them, 2) existing intermediate phalanges of paromomyids are inconsisten t with the "mitten gliding" hypothesis because they do not possess the dist inctive length and midshaft proportions characteristic of colugo manual int ermediate phalanges, and 3) paromomyids share with colugos and the scaly-ta iled squirrel Anomalurus several aspects of phalangeal morphology functiona lly related to frequent vertical clinging and climbing on large-diameter ar boreal supports. (C) 1999 Wiley-Liss, Inc.