Meeting Abstract
Two factors central to flight mechanics in birds are forces exerted by the flight muscles on the wing and wing shape that governs its aerodynamics. Wing shape has been linked to behavior, but comprehensive morphometric analysis of avian sternum shape has yet to be conducted, even though the sternum anchors the major flight muscles and its morphology is very diverse throughout Aves. Keel shape and size correlate strongly with flight muscle mass and keel position with mechanical advantage. Tracking disparity in wing and sternum morphology would provide a structural basis for comparing flight mechanics between modern birds and extinct taxa. Here, I examine wings and sterna of 82 “water birds” using two-dimensional geometric morphometrics on images of wings and of ventral and lateral sternal surfaces by applying both homologous landmarks and semi-landmarks. The resulting phylomorphospaces and statistical analyses reveal a high degree of convergence in both wing shape and sternum shape. Mapping body mass onto these phylomorphospaces suggests that body mass has less effect on constraining wing shape than sternum shape. The plot of wing shape space shows a relatively even scatter of low and high body masses throughout the occupied shape space. The ventral and lateral sternum shape spaces show significantly greater clustering within birds of smaller body masses and a wide spread of sternal shapes within birds of larger body masses. These results suggest that sternum morphology should be taken into account and analyzed with wing shape to more fully test coevolution, convergence, and disparity of functional adaptations in the forelimb and girdle for powered flight.
