Re: WING FEATHER ATTACHMENT

["Tim Williams" <twilliams_alpha@hotmail.com>]

Jim Cunningham wrote:

> > or steering (a la Garner et al.'s descending "pouncing proavis") would 
> it also
> > be a good idea to enhance your effective lift surface as well?.
>
> Sure, though I don't think it would happen because it was a 'good idea'.  
> I'd
> expect it to happen through random selection.

By "good idea" I meant "adaptively advantageous".  I was being very sloppy 
with my terminology.

> I also expect it would have been
> just as useful in escaping predators as in attacking prey.

Certainly.

> > Increasing stability might be an advantage at an early stage of proavian
> > evolution, when the biped just wants to alight feet-first (since the
> > forelimbs can't be used for support, like a cat).
>
> This seems to imply that the animal wants to be in flight before the wings 
> are
> developed, which I tend to think unlikely.

Actually I had Garner et al.'s "pouncing proavis" model in mind when I said 
this.  The orientational stability was useful in brief descents to the 
ground.  There is no flight in this incipient stage - just a controlled fall 
(i.e. parachuting).

> I'd prefer a scenario where the
> avian wings initially develop for some other purpose and gradually become 
> useful
> for flight.

Here it comes down to at what stage the wing started to become a 
lift-generator.  Of course, the tree-to-tree passive-glider-to-flight 
scenario favored by Feduccia (among others) emphasises the importance of 
lift in the development of the wing from the very beginning.  However, even 
if lift was not the primordial purpose of the proto-wing, the proto-wing may 
still have served an aerodynamic / aerial locomotive purpose, e.g.:
aerodynamic thrust --> aerodynamic lift (Burgers and Chiappe, 1999)
aerodynamic drag --> aerodynamic lift (Garner et al., 1999).

Or, was there an exaptive shift from a non-aerodynamic to an aerodynamic 
purpose, e.g. brooding --> flight (which has come up on this list once or 
twice)
    insect-catching nets --> flight (Ostrom's old idea, long discard)?

And then there is the cursorial theory of Caple and co., proposed in the 
1980's, in which the proto-wings acted as stabilizers during lunges at 
flying insects.  In this sense, the proto-wings were aerodynamic, but not 
aerial locomotive.


> Also, using the low aspect ratio tail to develop sufficient lift
> (upload) to offset the weight of the tail plus most of the weight of the
> hindlimbs will provide yaw stability while also providing an effective tail
> download that will enhance longitudinal stability  [snip] I'd
> expect the animal to be moving in the direction of decreased stability 
> almost
> from day one.

Hmmm...  that is an interesting idea.


References

Burgers, P. and Chiappe, L.M. (1999).  The wing of _Archaeopteryx_ as a 
primary thrust generator.  Nature 399: 60-62.

Garner, J.P., Taylor, G.K., and Thomas, A.L.R. (1999).  On the origins of 
birds: The sequence of character acquisition in the evolution of avian 
flight.  Proceedings of the Royal Society Biological Sciences Series B. 266 
(1425): 1259-1266.


Cheers, Tim


---------------------------------------------------------------------

Timothy J. Williams

USDA-ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163



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