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

[Tim Williams <twilliams_alpha@hotmail.com>]

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 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