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Re: Archaeopteryx not the first bird, is the earliest known (powered) flying dinosaur
--- Tim Williams <email@example.com> wrote:
> Jim Cunningham wrote:
> >I think maybe the reference to an airfoil may have
> been an inadvertant
> >misstatement? You realize of course, that airfoils
> are not necessary for
> >gliding. A thin, flat plank will glide quite well
> up to a lift cofficient
> >of about 1.0.
> I was being sloppy. What I was trying to say that
> an airfoil would make the
> pro-avian a better glider.
> >Why? I see the terrestrial requirements as easier,
> at least if you are
> >headed toward flapping flight.
> In this case, I meant 'easier' from a biomechanical
> standpoint. As you say,
> even a flat plank can glide to some degree; but it
> takes a lot more for an
> object (either animate or inanimate) to propel
> itself off the ground.
> One of the things I object to (and I think you'd
> probably agree) is the idea
> that flight *must* have evolved in the trees because
> it is 'easier', given
> that gliders can use gravity to their advantage
> every step of the way. To
> me, this seems irrelevent: the animal does not make
> a conscious decision
> about 'easy' and 'hard', it can only work with what
> it's got. Nevertheless,
> I think an animal that is fighting against the force
> of gravity would
> require more anatomical refinements (especially in
> the forelimb and pectoral
> girdle) than an animal that habitually glided with
> the assistance of
> gravity. In this sense, the flapper would accrue
> more pre-adaptations for
> powered flight than the passive glider. This is the
> strength of the WAIR
> model: characters and behaviors that assist in
> incline-running can be
> exapted toward powered flight, and even the
> incipient stages serve to
> benefit the animal.
> >As an aside, I'm neither a trees-down or ground-up
> guy. I think that is a
> >false dichotomy.
> Me too. Padian always hones in the fact that the
> most important development
> in the evolution of powered flight is the evolution
> of the flight stroke.
> In my experience, some gliding-to-flight models
> gloss over this detail.
> >That implies that good gliders don't evolve toward
> better gliders. If they
> >followed the scenario you describe, then we would
> expect the first flapping
> >flyers to have high aspect ratios. Does the fossil
> record support that?
> Don Ohmes answered Jim's question by saying...
> >I don't think the record does support early high
> aspect fliers (quite the
> >opposite, IIRC), a strong
> >piece of evidence against "trees down" for
> flappers, to go w/ the
> >theoretical objections Jim mentions.
> .... but I don't think we have the evidence yet to
> back this up. We would
> need theropods that exemplify the
> pre-_Archaeopteryx_ stage. The
> microraptorans/sinornithosaurs may approximate this
> pre-flight stage, but
> this is a leap of faith at the moment.
> Microraptorans/sinornithosaurs may
> actually represent a dead-end experiment in aerial
> locomotion, totally
> separate to birds.
I don't know either. However, I researched the
literature as well as I could 5-6 years ago. My
conclusion at that time was that, in birds, AR
generally increased through time to the present,
particularly within flightstyles (= NLR). At that
time, I took Archaeopteryx as a starting point, but
any reasonable (pre-Miocene) starting point post-arkie
comes out the same.
Question-- Why would we need
pre-arkie theropods? Be glad to have them, but your
point re deadends is valid.
> >I personally favor a flapping phase as a prelude to
> bird flight, but that
> >may be just my intuition at work. To me, nothing
> about bird flight implies
> >gliding as a beginning. Gliding isn't the easy way
> to start.
> Gliding *might* (and I stress *might*) be a good
> place to start if the
> animal is already spending its time in the trees and
> wants to get down to
> the ground fast, or to the next tree.
> >From a separate thread (put here to save
> bandwidth), Dan Varner wrote:
> << They're taking pictures of people posed in front
> of the giant gorilla.
> It's only an optical illusion. What she saw was a
> normal-sized gorilla
> standing next to Mayor Bloomberg.