My earlier research on the structural design of the limb skeleton of brachiating primates showed that the unique mechanics of limb loading in this group is correlated with only minimal morphological specialization of the forelimb skeleton (Swartz et al., 1989, Swartz, 1988, 1989, 1990a, 1990b). This suggests that the relationship between structure and function in mammalian limb bones can be a relatively weak one, and has led me to ask if this structure/function linkage is stronger in organisms for whom the consequences of deviations from mechanically optimal designs might be more extreme. In this light, the Order Chiroptera constitute an excellent model for several reasons: powered flight imposes extreme mechanical and energetic demands on the chiropteran locomotor system, raising the metabolic cost of deviations from optimal mechanical design; the nearest non-flying relatives of bats, the dermopterans and primates, provide considerable comparative information about the likely nature of bat ancestors; and the diversity in body size, flight style, wing shape, and phylogenetic affinity of the nearly one thousand extant species of bats furnish rich comparative material within the group.
