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

[don ohmes <d_ohmes@yahoo.com>]

--- Tim Williams <twilliams_alpha@hotmail.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.

Tim: 
> .... 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.

Don:

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.

Don

> >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.
> 
> 
> 
> ;-)
> 
> Cheers
> 
> Tim
> 
> 
>