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Re: Screaming dromaeosaur biplane killers of the air





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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