Meeting Abstract

54.4  Saturday, Jan. 5  Ontogenetic-Transitional Wing Hypothesis for the Evolution of Avian Flight DIAL, K.P.; Univ. Montana, Missoula kdial@mso.umt.edu

The evolution of avian flight remains one of biology�s major controversies primarily because discussions and publications on the subject repeatedly offer arm-chair functional interpretations of fossil forms as evidence for either an arboreal (tree down) or cursorial (ground up) origin of flight. Despite repeated emphasis on the �wing-stroke� as a potentially fruitful avenue of investigation for addressing the evolution of flight, no empirical data exist on wing-stroke dynamics in an experimental evolutionary context. Recent studies using flow visualization (DPIV, Tobalske and Dial 2007) and wing kinematics (Dial, Jackson and Segre, in review) of developing ground birds provides novel insight into the function of proto-wings in extant species and is argued to offer correlative data for extinct forms. We now recognize that proto-wings have a function in all ground birds, as well as many other species of birds, in that developing forelimbs assist the animal to reach elevated refuges by supplementing the hindlimbs and flapping proto-wings also permit the animal to descend safely by reducing impact velocity. Here I offer an Ontogenetic-Transitional Wing Hypothesis which posits that the incremental adaptive stages leading to the evolution of avian flight correspond behaviorally and morphologically to transitional stages observed in ontogenetic forms. This hypothesis builds on the WAIR Hypothesis (Dial, 2003) and differs from other published accounts in that it is flap-based (in contrast to requiring a gliding precursor), involves an aerodynamically functional proto-wing, incorporates both the simultaneous and independent use of legs and wings, is consistent with fossil forms possessing long legs and proto-wings, and assumes that a fundamental wing-stroke was established for aerodynamic function early in the bipedal ancestry leading to birds.