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Re: Arms into wings



In a message dated 3/4/99 2:30:04 PM EST, TomHopp@aol.com writes:

<< In a message dated 3/3/99 8:53:02 PM, Dinogeorge writes:
 
 << Roadrunners are already quite capable fliers, so the point is moot: In
this
 instance, flight did indeed come first. What you want is a bird that exhibits
 this kind of behavior but whose lineage is entirely flightless (not just
 secondarily flightless)--and there is no such bird extant. >>
 
 Absolutely not true that it is moot. The roadrunner's leaping, flapping
 behavior is quite sufficient as a model of the brooding-to-flight transition
 regardless of the roadrunner's past evolutionary history. >>

Here's where your model is moot: I assert that the roadrunner is even better
as a model of a bird in the process of >losing< (not acquiring) its flying
ability--a stage in the evolution of a secondarily flightless, ground-dwelling
cursorial form from a flying ancestor. Certainly the roadrunner's ancestral
forms were better fliers than it now is, so to that extent the model of a
roadrunner as being on the way to secondary flightlessness is more true to
life than any model of a roadrunner as a flightless, cursorial form evolving
flight in a ground-up scenario. Thus, since the model can unquestionably be
used to support two opposing scenarios, it is moot by definition.

Imagine the roadrunner with more primitive, archaeopterygid wings--with claws
and separate fingers--and a bit less advanced skull morphology than seen in
_Archaeopteryx_, and you have an >excellent< facsimile of the ancestral
dromaeosaurid and how such a form might have behaved. It would >naturally<
have used its still-powerful wing stroke in conjunction with its claws to
dispatch prey: exactly the forelimb movement that gives the group Maniraptora
its name. It would have used its long tail for balance and powerful hind limbs
for running and leaping >just like< the roadrunner does. These behaviors would
have been selected for and evolutionarily augmented, improved, and tuned,
eventually giving us the dromaeosaurids that we find in the fossil record.