Re: Screaming dromaeosaur biplane killers of the air

["Tim Williams" <twilliams_alpha@hotmail.com>]

Greg Paul <SP1954@aol.com> wrote:

> What has never been really clear is why protobirds would develop leg wings 
> and then lose them.

In my view, that question is quite easy to explain...

Modern gliding mammals show a membrane (patagium) that is strung between the 
forelimbs and the hindlimbs.  Thus, all four limbs are involved in 
supporting the gliding surface.  This arrangement is what has been posited 
for the ancestors of pterosaurs - sort of like _Sharovipteryx_ (assuming the 
patagium did stretch from the forelimbs to hindlimbs, and was not just 
attached to the hindlimbs and tail.)

Thus, under this hypothesis, the transition from gliding "proto-pterosaurs" 
to pterosaurs capable of powered flight is marked by a change in the 
relative contributions of the fore- and hindlimb to the flight surface.  In 
pterosaurs, the forelimbs are highly elongated, the pectoral girdle works 
the flight surface, and the participation of the hindlimbs is minimal (if 
any, at least in certain species).

If one hypothesizes that birds evolved from _Microraptor_-like ancestors, 
then a similar pathway would be invoked: Four-limbed glider to two-limbed 
flier.  Unlike pterosaurs, the "protobirds" show a discontinuous gliding 
surface, making it much easier to decouple the hindlimbs from the flight 
surface.  This implies the absence of hindlimb feathers in _Archaeopteryx_ 
and other primitive birds is secondary - if you don't use 'em, lose 'em.

> Suddenly making dromaeosaurs nondinosaurian birds will only
> show a state of embarrasing desperation. It's a hopeless case.

It's a constant source of amusement to me.  As soon as one theory on why 
birds CANNOT be dinosaurs is demolished by a new discovery, the 
birds-are-not-dinosaurs crowd come up with a new theory even less plausible 
than the previous one.  As I've said before, over the past ten years these 
folks have adopted more positions than the Kama Sutra.



Tim

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