Meeting Abstract

P1.198  Friday, Jan. 4  The function of avian distal wing bones during flight CRANDELL, KE; University of Montana, Missoula kristen.crandell@umontana.edu

Avian wing bones have specialized via fusion and reduction to form a four-bar automatic linkage system and reduce distal limb mass. Given this reduction, the complexities of wing motion during upstroke are surprising. We undertook the present study to better understand skeletal mechanisms of the linkage system and wrist. Wrist bones have been highly reduced to two main bones: the radiale and the ulnare. These two bones have specific morphologies that correlate with wing stroke style during slow flight. Early studies of morphology suggest that the wing tip reversal upstroke style occurs due to a passive interaction between the wrist bones. To produce the pronation of the manus during upstroke, the ventral ridge of the carpometacarpus is thought to slide along the ventral ramus of the ulnare. During downstroke, this same morphology is thought to transfer distal force on the wing from the carpometacarpus to the ulna. These key morphological features of the wrist are relied heavily upon as diagnostic clues toward aerial or terrestrial lifestyle of fossils. As these predictions are based off of morphology alone, here we explored the interaction of the distal wing bones in the pigeon during slow level flight, using bi-planar fluoroscopy and marker-based XROMM to reconstruct 3-D motion. Our data suggest that the manus operates independently of both the radiale and ulnare during upstroke. Further, we find preliminary evidence that supports a “flat plate” hypothesis: each bone element appears to follow as predicted by an automatic linkage system during downstroke and provide a unified, flat 4-bar system. NSF IOS-0923606 and IOS-0919799.