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AW: Dinosaur Fore Limb Posture & Evolution of Avian Flapping Flight Stroke



> http://tinyurl.com/cdleeq

"Ontogenetic and behavioural 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 10Hz, forelimb 
stroke-angles in excess of 130Â, 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., pre-bird), in the absence of a living analogue, a new approach 
using Strouhal number (St=fÂA/U) is championed. Strouhal number is a 
non-dimensional number that describes the relationship between wing-stroke 
amplitude (A), wing-beat frequency (f) and flight speed (U). Calculations 
indicate 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 â required for gliding and flapping 
flight â evolved from an alternating forelimb motion, evident in all extant 
bipeds when running except birds."

Cool! One might try and glean some angles to estimate A from here 
http://www.app.pan.pl/article/item/app51-305.html?pdf=39 and see what minimum f 
would cause U to exceed stall speed in different taxa.


Regards,

Eike