The tail is central to the origin of avian flight. However, despite extensive attention to the wing, the tail of birds has not been the focus of developmental, functional or paleontological studies. Modern flying birds possess a very short tail compared to Archaeopteryx and other theropod ancestors. Tail reduction is the product of fewer caudal vertebrae and the fusion of distal segments into a uniquely avian structure, the pygostyle, which forms a base for the tail feathers. In this research project, the PI will combine approaches from several disciplines to study the evolution of this caudal morphology in birds. (I) The quail-chick chimera technique will be employed for a description of normal tail ontogeny and for experiments to elucidate mechanisms of segment number regulation and pygostyle formation. (II) The motor control and kinematics of the tail will be quantified in a functional study of the pigeon during eight locomotor modes. (III) Pertinent fossil birds will be reevaluated in light of the new information obtained in (I) and (II). Results from these studies will have significance for each individual field. However, the unprecedented integration of information from these three disciplines within a phylogenetic framework will provide a more global perspective for evaluating how developmental, functional and phylogenetic influences facilitate or constrain the evolution of form.
