Locomotor ontogeny and the evolution of avian flight

Meeting Abstract

92.5  Saturday, Jan. 7  Locomotor ontogeny and the evolution of avian flight HEERS, Ashley M.*; DIAL, Kenneth P.; University of Montana; University of Montana ashmheers@gmail.com

Fossils with transitional morphologies are the record of major evolutionary transformations key to understanding life’s history. Reconstructing these transformations requires interpreting functional attributes of extinct forms by exploring how similar features function in extant organisms. Yet extinct-extant comparisons are often difficult, because extant adult forms frequently differ substantially from fossil material. Here, we illustrate how postnatal developmental transitions in living birds can provide rich, novel insight into the evolution of avian flight. As developing birds acquire flight capacity, ontogenetic changes in feather and skeletal morphology tend to parallel evolutionary changes in the theropod ancestors of birds. Examining locomotor ontogeny may thus clarify potential locomotor capacities of extinct theropods, by elucidating relationships between form, function, and behavior during obligately-bipedal to flight-capable transitions. To document feather and skeletal ontogeny in the precocial chukar (Alectoris chukar), we (i) used a propeller apparatus to measure aerodynamic forces generated by dried chukar wings over a range of ages and Reynolds numbers, and (ii) used high resolution CT scans and biplanar x-ray videos (X-ray Reconstruction of Moving Morphology) of different aged chukars to quantify 3D skeletal kinematics during various behaviors. Our results show that juveniles and adults with highly disparate anatomies employ remarkably similar skeletal kinematics, possibly due to differences in aerodynamic force production. These findings are important for understanding flight ontogeny and evolution. Similarities between developing birds and extinct theropods are merely one of many parallels between ontogeny and evolution, and exploring the ontogeny of morphological form and functional capacity may thus provide rich insight into a broad array of evolutionary transformations.

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