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Re: Phylogeny of Maniraptora



Graydon <oak@uniserve.com> wrote:

Are there any non-volant organisms that really glide, rather than
parachuting?   [snip]
I'm trying to get at a distinction between using aerodynamic forces to
reduce sink rate (parachuting) and turning velocity into actual lift
(gliding).

Many biologists are not too crazy about the classic aerodynamic distinction between "parachuting" and "gliding". For example, one traditional definition of the two is based on the animal's angle of descent from the horizontal: > 45 degrees for parachuting, < 45 degrees for gliding. However, animals are not paper airplanes; they can often propel themselves into the air, and alter their angle of descent. Thus, many biologists prefer to look at the posture or anatomical adaptations of aerial locomoting animals, to determine if the animal in queston is endeavoring to increase drag or lift in its aerial behavior. This approach is a lot fuzzier than mathematical formulae, but remember we are dealing with real-life organisms here.





Tim

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