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1 April 2009 Forelimb Posture in Dinosaurs and the Evolution of the Avian Flapping Flight-Stroke
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Abstract

Ontogenetic and behavioral studies using birds currently do not document the early evolution of flight because birds (including juveniles) used in such studies employ forelimb oscillation frequencies over 10 Hz, forelimb stroke-angles in excess of 130°, and possess uniquely avian flight musculatures. Living birds are an advanced morphological stage in the development of flapping flight. To gain insight into the early stages of flight evolution (i.e., prebird), in the absence of a living analogue, a new approach using Strouhal number (St = f f · A/U) was used. Strouhal number is a nondimensional number that describes the relationship between wing-stroke amplitude (A), wing-beat frequency (f), and flight speed (U). Calculations indicated that even moderate wing movements are enough to generate rudimentary thrust and that a propulsive flapping flight-stroke could have evolved via gradual incremental changes in wing movement and wing morphology. More fundamental to the origin of the avian flapping flight-stroke is the question of how a symmetrical forelimb posture—required for gliding and flapping flight—evolved from an alternating forelimb motion, evident in all extant bipeds when running except birds.

© 2009 The Society for the Study of Evolution.
Robert L. Nudds and Gareth J. Dyke "Forelimb Posture in Dinosaurs and the Evolution of the Avian Flapping Flight-Stroke," Evolution 63(4), 994-1002, (1 April 2009). https://doi.org/10.1111/j.1558-5646.2009.00613.X
Received: 9 April 2008; Accepted: 1 December 2008; Published: 1 April 2009
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