Flight is a truly distinctive locomotor mode: it makes extreme demands on an organism's morphology and physiology, and produces profound ecological and behavioral consequences. In the hundreds of millions of years that vertebrates have inhabited the earth, only three lineages have evolved the capability of sustained flight: the extinct pterosaurs among reptiles; the birds; and within mammals, the (Order Chiroptera). Perhaps because of the ecological opportunities available to nocturnal flying animals, the success of bats has been extraordinary by any measure. Today, bats are more abundant than any other mammalian order in number of individuals and are second only to the rodents in number of species, with over 900 species of living bats described. Furthermore, bats are more widely distributed than any other mammals except humans and cetaceans (whales and porpoises). Most authors have attributed the tremendous evolutionary radiation of bats to the key adaptive innovation of powered flight, even while our understanding of this evolutionary transformation has remained rudimentary. Bats fly using wings that are clearly derived from successive modifications of the primitive mammalian limb design, retaining the basic topological interrelationship of forelimb skeletal elements even while certain aspects of the morphology of the bony elements and the surrounding soft tissues have been greatly altered. In particular, changes have occurred in the proportions and shape of the limb skeleton; the geometry and mobility of the forelimb joints; the attachment points, internal architecture, and physiological capabilities of muscle tissue; and the distribution of mass within the body. We have yet to explore how the wing skeleton functions during flight or the nature of the bony material in wings. This project will test the hypothesis that skeletal composition and limb bone architecture in bats relate directly to the strenuous mechanical demands placed on the wing skeleton during flight. We will explore the possibility that the mineral content and basic properties of bat wing bones differ significantly from other mammals, and determine the stress flight places on wing bones during flight. This case study will be an important test of the general hypothesis that the structural design of limbs in vertebrates is determined by the functional requirements of locomotion.