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Re: bauplan convergence



At 02:25 AM 6/17/00 -0700, Scott Hartman wrote:
Gravity can get ANYBODY to the ground that leaps out of a tree.

Gravity, air, and a little extra skin on the arms gets you >>parachuting.

But parachuting doesn't require that you flap.

Actually, while the term "parachuting" is bandied about by many when discussing incipient levels of gliding, this usage is innappropriate. Balda et al. (1984 Archaeopteryx conference volume)provide a more aerodynamically correct definition of parachuting as a method to slow descent using only drag (or at least where lift is negligable). Animals that can glide at a measly 45 degree angle from the horizontal are still creating lift at an impressive 70% of body mass. Few, if any animals qualify as parachuters (although perhaps flying frogs are an exception?) That's why flying squirrells and snakes have flat bottoms but round(er) tops.

I am aware of the difference. I was thinking that drag-based reduction of fall rates might precede the more specific adaptations establishing lift surfaces.


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May the peace of God be with you.         sarima@ix.netcom.com