Meeting Abstract

S10-8  Thursday, Jan. 7 13:30  Building a Bird: Ontogenetic and Evolutionary Construction of the Avian Body Plan HEERS, A.M.; American Museum of Natural History

Developmental and evolutionary origins of avian flight involve some of the greatest transformations in vertebrate history. Flight is the most power-demanding mode of locomotion, and volant species have many anatomical features that presumably help meet these demands. However, juvenile birds, like early winged dinosaurs, lack many hallmarks of advanced flight capacity. Instead of large wings they have small “protowings”, and instead of robust, interlocking forelimb skeletons their limbs are gracile and their joints less constrained. Such features are often thought to preclude extinct theropods from powered flight, yet young birds with “dinosaur-like” anatomies flap-run up slopes and even briefly fly, thereby challenging longstanding ideas on skeletal and feather function in the theropod-avian lineage. To address this discrepancy and assess how ontogenetic changes in anatomy effect improvements in locomotor performance, I constructed three-dimensional musculoskeletal models of a precocial ground bird (Alectoris chukar) (Software for Interactive Musculoskeletal Modeling) and simulated flapping behaviors at different ontogenetic stages (OpenSim). Aerodynamic measurements, in vivo kinematics and model simulations collectively suggest that immature birds have excess muscle capacity and are limited most by feather morphology, which they compensate for by using their wings and legs cooperatively until the wings can fully support body weight during flight. These results help elucidate the ontogeny and evolution of avian locomotion by (i) establishing how muscular and aerodynamic forces interface with the skeletal system to generate movement in morphing juvenile birds, and (ii) providing a benchmark to inform biomechanical modeling and simulation of extinct theropods with similar anatomies.