The Aerodynamically Streamlined Body Shape of Birds: Implications for the Evolution of Birds, Feathers, and Avian Flight

摘要

Birds are likely to have evolved from an ecologically and locomotorily polyvalent, lizard-like reptilian ancestor. The evolutionary transformation of an ancestral unfeathered reptilian integument into a feather-bearing avian integument is proposed to have been driven by a selective regime favoring aerodynamically streamlined body contours to maximize leaping with adducted forelimbs between trees and branches. Spreading of the forelimbs was first part of landing maneuvers; wing fluttering and flapping would have increased control. Flapping flight evolved from a stage of flap-bounding to extend leaps. A stage of gliding with outstretched forelimbs is unlikely to have been part of these evolutionary transitions.