Meeting Abstract

3.1  Tuesday, Jan. 4  Developing skeletons in motion: the ontogeny of skeletal form and function in a precocial ground bird (Alectoris chukar) HEERS, AM*; BAIER, DB; JACKSON, BE; DIAL, KP; U of Montana; Providence college; U of Montana; U of Montana ashmheers@gmail.com

Juvenile birds are capable of remarkable locomotor behaviors, despite having a rudimentary and underdeveloped skeletal system. Compared to adults, the forelimbs and hindlimbs of immature birds are less ossified and lack the fusion of distal bony elements into a carpometacarpus and tibiotarsus. In order to document the ontogeny of skeletal form and function, we used high resolution CT scans and biplanar x-ray videos (XROMM; X-ray Reconstruction of Moving Morphology) to quantify 3D skeletal kinematics during running, flying, and wing-assisted incline running (WAIR) in a developmental series of a precocial ground bird, the chukar (Alectoris chukar). Across clades, flight-incapable juveniles engage the forelimbs and hindlimbs simultaneously during WAIR or similar behaviors in order to escape from predators and reach refugia. Thus, understanding the ontogenetic relationship between forelimb and hindlimb skeletal form and function is critical to understanding flight ontogeny and juvenile survival. Given that the evolutionary origin of avian flight is documented only by fossilized bone and feathers, ontogenetic relationships may additionally provide insight into flight evolution. As developing ground birds transition from obligately-bipedal juveniles to flight-capable adults, increases in skeletal fusion of the distal limbs appear to mimic evolutionary patterns of skeletal fusion in theropod dinosaurs and early birds. This kinematic analysis of locomotor ontogeny therefore has developmental and evolutionary implications, and represents the first 3D kinematic quantification of skeletal function in animals that rely on developing skeletons to locomote and survive.