A fundamental avian wing-stroke provides a new perspective on the evolution of flight

Article

关键词: MANEUVERING FLIGHT;    WIDE-RANGE;    ORIGIN;    AERODYNAMICS;    KINEMATICS;    BIRDS;   

DOI  :  10.1038/nature06517

来源: SCIE

【 摘 要 】

The evolution of avian flight remains one of biology's major controversies, with a long history of functional interpretations of fossil forms given as evidence for either an arboreal or cursorial origin of flight. Despite repeated emphasis on the 'wing-stroke' as a necessary avenue of investigation for addressing the evolution of flight(1-4), no empirical data exist on wing-stroke dynamics in an experimental evolutionary context. Here we present the first comparison of wing-stroke kinematics of the primary locomotor modes (descending flight and incline flap- running) that lead to level- flapping flight in juvenile ground birds throughout development (Fig. 1). We offer results that are contrary both to popular perception and inferences from other studies(5-7). Starting shortly after hatching and continuing through adulthood, ground birds use a wing- stroke confined to a narrow range of less than 20 degrees, when referenced to gravity, that directs aerodynamic forces about 40 degrees above horizontal, permitting a 180 degrees range in the direction of travel. Based on our results, we put forth an ontogenetic- transitional wing hypothesis that posits that the incremental adaptive stages leading to the evolution of avian flight correspond behaviourally and morphologically to transitional stages observed in ontogenetic forms.

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