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Re: Archaeopteryx not the first bird, is the earliest known (powered) flying dinosaur
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
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 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.