FUNCTIONAL-MORPHOLOGY OF THE LEMURIFORM WRIST JOINTS AND THE RELATIONSHIP BETWEEN WRIST MORPHOLOGY AND POSITIONAL BEHAVIOR IN ARBOREAL PRIMATES

A comparative study of carpal joint structure and function in six Mala gasy lemuriforms was undertaken to test predicted morphoclines in carp al joint morphology between pronograde and orthograde arboreal primate s. Patterns of movement at the wrist during locomotion were observed a nd described for the lemuriform species Lemur fulvus and Propithecus v erreauxi. Lemur fulvus, which assumes a pronograde posture during loco motion, extends and pronates the wrist during the support phase of qua drupedal walking and running stride cycles. Furthermore, the forearm o f this species exhibits some transverse movement across the proximal w rist joint during the support phase. In contrast, the indriid Propithe cus maintains the hand and wrist in a flexed and partially supinated p osition during vertical clinging and suspensory postures. Habitual qua drupedal and vertical postures in Malagasy primates are in turn relate d to very different patterns of carpal joint morphology and articular mechanics. Those lemurs which are predominantly pronograde share a ser ies of structural features related to stabilizing the antebrachiocarpa l joint during extension and mediolateral deviation and the midcarpal joint during pronation: an intraarticular labrum is present on the inn er portion of the radiocarpal ligament, the radiocarpal articular surf ace is quite flat dorsoventrally, the capitate-trapezoid embrasure is expanded dorsally, and development of the radial and ulnar styloids is more pronounced. The wrists of Propithecus, Avahi, and Lepilemur (ver tical clingers) differ from those of quadrupedal lemuriforms in posses sing a suite of morphological features related to stabilizing the wris t during antebrachiocarpal flexion and midcarpal supination: the radio carpal articular surface is deeply curved and tilted anteriorly, the d orsal radiocarpal ligament is very broad, thick, and fibrous, the hama te's triquetral facet is directed proximodistally, and the capitate-tr apezoid embrasure is dorsally constricted and expanded palmarly. These observed contrasts in carpal form and function are used to define fur ther the morphological features related to orthograde posture in sever al lineages of arboreal primates. (C) 1996 Wiley-Liss, Inc.