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

[don ohmes <d_ohmes@yahoo.com>]

--- jrc <jrccea@bellsouth.net> wrote:

> 
> ----- 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?

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 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 
> 
>