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Re: flapping from gliding



Achut Reddy wrote:

> First, yes, gliders have something resembling a wing, but it takes
> a lot more than a flap of skin to achieve true powered flight. 
> Such as: a strong breastbone for flight muscle attachment,
> shoulder support, great muscle coordination, high intelligence, 
> high metabolism, lightweight construction, good vision, etc., etc.
> A glider would have to evolve all of these things in much the
> same way a cursorial animal would.  Except, the cursorial flight-origin
> candidates already have a head start on most of these things.

     Archaeopteryx did not possess a keeled sternum for attachment of the 
big pectoralis muscles.  In modern, endothermic birds, these muscles are 
essential for providing the extra power boost needed for a ground 
takeoff, although once airbourne, the smaller pectoralis minor and 
shoulder muscles can sustain flapping flight.  If Archaeopteryx was 
endothermic, it may have had problems taking off if it wasn't starting 
out in the trees.
     Ruben made the suggestion that Archaeoptery was a "ground up" 
ectothermic flier.  He asserts that reptilian muscle has (more? better) 
mitochondria, which allow greater bursts of energy than mammals are 
capable of.  With these, Archaeopteryx may have been able to produce the 
thrust needed for a ground takeoff.  I can't remember the metabolic 
details, its been about six months since I read his paper.
     I have heard objections to this idea, including the claim that the 
wrist in Archaeopteryx was not reinforced as it is in modern birds, so 
the extra burst needed for takeoff couldn't have been supported by the wrist.

LN Jeff
"Hariet...Har-ee-et...hard hearted harbinger of haggis..."