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Dinogeorge wrote:
> Paleontologists have become so enamored of exaptation that they have a tendency to see it > everywhere.
No, they just see these exaptive changes when the evidence points to them.
> But birds have so many very flight-specific adaptations and autoapomorphies that it is > EXTREMELY unlikely that they ALL arose as non-flight-related exaptations.
I never said "ALL". Where are you getting this from? Many flight-related features in modern bird arose for other purposes (maybe predation, maybe climbing, maybe gliding). Other flight-related features arose because of flight (such as the alula). I'm not putting all my eggs in one basket, and nor should you. I think you should re-read some of the studies done by paleontologists. Some of your criticisms are way off base.
> We're not talking one-in-a-million unlikelihood here, we're talking one-in-10^50 or so.
Again, this is an unsubstantiated claim.
> When we see a random assortment of birdlike features in a ground-dwelling theropod--and >different theropods exhibit different assortments of these--it is because these
> features were retained (those that were not lost or modified away) from a
> previously volant ancestor, not because they somehow accumulated to "prepare" or
> "predispose" the theropod's descendants for future flight, in an aerial regime from which the > theropod is entirely removed.
There is several things wrong with the above opinion. Firstly, there was no "preparation" or premeditation involved in the accumulation of these characters. For example, longer arms might have originally evolved to increase the reach of prey-catching theropods. Feathers probably originally evolved for insulation/thermoregulation - as in modern down feathers. There is no reason to believe that EVERY flight-related character seen in birds had its genesis in powered aerial behavior.
Secondly, your assertion that theropods were "entirely removed" from an "aerial regime" - this is ludicrous. There is plenty of evidence that non-avian theropods could climb trees, and could glide as well. Just look at _Microraptor_, or _Pedopenna_, or _Epidendrosaurus_, or _Yixianosaurus_.
> When secondary flightlessness occurs in modern birds, the wings of the
> ancestral form are too strongly modified for flight and are usually simply
> vestigialized (or even lost entirely) in the flightless descendant. Now suppose the
> ancestral form is an archaeopterygid-like Mesozoic bird (or an even less
> birdlike ancestral form of such), with clawed wings that retain much of their
> original grasping-hand function. In a flightless descendant of such an ancestor,
> the forelimbs might reduce, but they could certainly retain their grasping
> hands with
claws (as an exaptation!) for a predatory function. Voila, we have
> the archetypal theropod. All it has to do is get big--like lots of modern
> flightless birds have.
It's a nice story - but it has absolutely no support from the fossil record. No matter how plausible or alluring a theory may sound in the beginning, it must be stacked against the available evidence.
Tim
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