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Re: Archaeopteryx and Flight



On Fri, 23 Dec 1994, Chas Bedford wrote:

> 
> Isn't this the whole point of natural selection?? (At least by my (educated
> layman's) understanding) If you are being chased up a tree by a predator
> you may have a choice between being caught (and eaten) or making a jump for
> it. If you have the gliding characteristics of a brick, you go splat. OTOH,
> if your feathers or wing membranes are a bit bigger than average (and/or
> your arm muscles are a bit stronger) you may just get a bit of lift, make
> it to the next tree and survive to breed.

Yes, but that is my point. If the traits needed were not there BEFORE 
they went into the trees, then they WOULD have all the gliding char's of 
a brick (or at least of a small-medium sized animal). They must have had 
these characteristics (ie. elongated feather-like structures, probably 
some gliding ability) BEFORE they took to the trees. I can't see the 
proto-archies climbing featherless into the trees and THEN 
developing long fragile feathers. There is too much danger in damaging 
them when climbing around, and they would tend to get in the way too much 
for the advantage of _occasionally_ having to leap from a tree to save 
itself to have much effect.

> webbing in the right place. In proto-birds AIUI feathers could have evolved
> for some entirely different reason (e.g. thermal regulation) and the first
> improvements in gliding or parachuting ability would have been quite
> fortuitous. However, once a survival advantage is gained, natural selection
> could convert an exadapted feathered arm into a proto-wing.

You won't get an argument from me on this either. My only thought is 
whether it is more likely that these initial processes developed before 
or after the ascent into the trees. I tend towards before since I can see 
little purpose for the interim steps when living in a tree.


> As a layman and ex-lurker, I hope everybody will be gentle with me as well.

Don't count on it; they're all killers around here. ;-)


Shaun Sinclair
        ssinclai@gpu.srv.ualberta.ca