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In a message dated 95-12-01 02:20:28 EST, ornstn@inforamp.net (Ronald
Orenstein) writes:

>A thought on this - most, if not all, of the living specialized gliders are
>either quite functional quadrupeds or (in the case of the flying snake)
>equally able to move freely within a canopy.  Bipeds, on the other hand, may
>be less adept at clambering about in trees - perhaps they are more likely to
>evolve flapping mechanisms  as an assist in this?  Of course this is
>probably meaningless for bats and pterosaurs, pace Kevin Padian.

Most gliders, of course, never evolve powered flight. They evolve other
specializations toward becoming better gliders, either because their
particular gliding adaptations prohibit (or at least render extremely
unlikely) the evolution of flight (e.g., flattened ribcages) or simply
because the requisite adaptations simply did not appear in their lineages.

>As noted above I think this would certainly drive flight, once it had
>evolved, towards greater efficiency, but the first steps towards flight must
>have been driven by the need to travel much shorter distances - a sort of
>assisted leap.

A long tail will help to keep a gliding animal aloft while its forelimbs
undergo the required incremental changes from unpowered-gliding organs
through powered-flight organs. The earliest pterosaurs and birds all had long
tails and rear flight surfaces (the earliest bats are unknown, but I bet they
had long tails, too), and these were discarded through evolution (too much
drag) once powered flight was achieved.