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Re: Resolving the Digit Loss Debate?

> Early dinobirds had five loci for airfoils on their body: the tail and the
> four limbs. The first of these to develop an airfoil function must have
> the tail, mainly because it's simply the part that needs the least
> modification to become one: just grow a fringe of feathers and voila.

A parachuter or glider with elongated feathers on its tail only must have
odd aerodynamic behavior... I suspect the effect would be that the poor
beast would fall down head-first instead of belly-first... could HP Jim
Cunningham enlighten us on this? :-)

> With
> regard to the limbs, they don't have to be able to extend sideways from
> body (let alone up over the back as in avialan birds) in order to have an
> aerodynamic function; given a suitable fringe of feathers, they can be
> aerodynamic at pretty much any angle.

If the ancestral dinosaur was a quadrupedal sprawler, however, it is very
unlikely to have given up sprawling in the trees, where limb mobility is
always an advantage!

> We're not looking for perfect flight
> here, just something to mollify the effects of a fall (as in fluttering)
> to help control the midair course of a leap.

That something should be able to evolve from something that's already here,

> The forelimbs would naturally
> have served to arrest the animal at the end of a leap, so there would be a
> tendency to retain/improve the grasping function for this new role.

Sure, but why a tendency to make the playing-the-piano position for the
hands impossible? And why the loss of fingers??? The hands of theropods
could arrest them only when they crash _laterally_ into a trunk, not
ventrally, AFAIK (but the feet could accomplish this).