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

[jrc <jrccea@bellsouth.net>]

----- Original Message ----- 
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Tuesday, December 06, 2005 2:19 PM
Subject: Re: Archaeopteryx not the first bird, is the earliest known 
(powered) flying dinosaur


> To me an "incipient glider" is a parachuter: the animal cannot yet produce 
> an airfoil, but the skeletal proportions and integument are sufficient to 
> slow and perhaps guide its descent to the ground.

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 don't want to get bogged down in the old 'ground-up' vs 'trees-down' 
> dichotomy, but if the ancestors of birds evolved flight in a terrestrial 
> setting then the requirements become a little steeper.

Why?  I see the terrestrial requirements as easier, at least if you are 
headed toward flapping flight.  As an aside, I'm neither a trees-down or 
ground-up guy.  I think that is a false dichotomy.

> By contrast, a passive gliding stage is 'easier' in the sense that the 
> evolution of a lift-and-thrust-generating stroke and more heavy-duty 
> pectoral musculature can be deferred.

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?

> But I don't think we are at the point where we can dismiss the role of a 
> terrestrial component in the evolution of avian flight, so all options are 
> still on the table.

I do agree with that.

> I personally favor a gliding phase as a prelude to powered flight, but 
> this is just my intuition at work;

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.

> and I cannot use my intuition alone to trump the work of people like 
> Burgers and Chiappe and Dial who demonstrated (both theoretically and 
> experimentally) that a 'ground-up' model of avian flight is feasible.

Me, neither.

> > , as though nonavian dinosaurs were for some reason not allowed to be true 
> > fliers. Very odd.

I think this is well said.

> Successful gliding is an aerodynamic feat that requires a considerable 
> anatomical investment on the part of the glider.

This is true.  It's a lot tougher than flapping beginnings.

Jim