Meeting Abstract
In the process of invading aerial media, birds and theropod dinosaurs have undertaken some of the most dramatic morphological and functional transformations in the history of vertebrates. Flight is the most physically demanding form of locomotion, and flight-capable adult birds possess many anatomical features that are presumably adaptations or exaptations for meeting such demands. Juvenile birds, like early winged dinosaurs, lack the hallmarks of advanced flight capacity. Instead of large wings they have small “protowings”, and instead of the robust, interlocking forelimb skeleton associated with powerful and highly canalized flight strokes their limbs are more gracile and their joints less constrained. Such features are long assumed to have precluded early theropods from powered flight, yet immature birds with dinosaur-like anatomies engage their incipient wings to flap-run up slopes and even briefly fly. How is this accomplished? Using SIMM (Software for Interactive Musculoskeletal Modeling) and OpenSim, we constructed biomechanical models of a bird (Alectoris chukar) at different ontogenetic stages, to assess how changes in anatomy effect improvements in locomotor performance during posthatching development. Our results suggest that immature and adult birds with different skeletal morphologies can perform similar skeletal kinematics by producing and resisting different amounts of aerodynamic force during a given behavior. This type of work can help elucidate the ontogeny and evolution of avian locomotion by establishing how muscular and aerodynamic forces interface with the skeletal system to generate movement in morphing juvenile birds, and by using juveniles to inform biomechanical modeling of extinct theropods with similar anatomies.
