MIDDLETON, K.M.; GATESY, S.M.; Brown University, Providence, RI; Brown University, Providence, RI: Wing Design and Disparity in Flying Vertebrates

The three vertebrate lineages in which powered flight arose faced similar mechanical demands when interacting with their fluid environment. The ancestors of pterosaurs, birds, and bats lengthened and broadened their forelimbs into aerodynamic appendages. Similarity of wing shape potentially resulted from the presence of aerodynamic constraints on performance of flapping appendages. However, because each lineage arose from a different pre-flight ancestor, the solutions to such common constraints varied, and each clade exhibits unique specializations. In this analysis, we addressed broad questions of wing design, such as: are wings highly constrained by aerodynamic requirements?; have pterosaurs, birds, and bats converged on a single wing form?; and, are some volant clades more morphologically diverse than others? Ternary diagrams were used to explore variation in skeletal and segmental proportions and patterns of disparity in vertebrate wings. We found ternary diagrams more informative than simple ratios of humerus to radius or humerus to ulna (brachial index), which neglect important variation. Our results show that vertebrate wings are neither widely nor evenly distributed in ternary morphospace and that extreme limb proportions are absent. Bird and bat skeletal wing proportions are distinct from one another, but pterosaur proportions overlap both. Novel patterns emerge when the wing is divided into functional segments and plotted on a ternary diagram. The proximal and middle segments are still roughly equal, but the distal segment is by far the longest at 40-86% of wing length. Each clade occupies a distinct region of morphospace suggesting different solutions to common aerodynamic constraints. However, other wing functions such as terrestrial locomotion (pterosaurs and bats) should not be ignored as factors contributing to wing design.