Re: The Lizard of Oz

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

David Marjanovic wrote:

> This implies that either bird ancestors dropped from low heights -- 2 m or
> less, I guess -- or that they already had something to retard their
> descents.

Both are possibly true.  Feathers could serve to create drag, in addition to 
their insulatory properties.

> This _could_ explain the evolution of wing feathers

I think it does.  Stability and control during leaping would select for 
stiffer and more elaborate feathers on the forelimb (starting at the manus) 
and perhaps on the end of the tail too.  The feathers would have symmetrical 
vanes.  In other words, symmetrical remiges and rectrices evolved as 
drag-creating devices.  (I can't claim credit for this idea - it's part of 
Garner et al.'s "Pouncing Proavis" model.)

> (I prefer brooding for this),

Maybe they used them for brooding as well.  Wonderfully versatile things, 
feathers.

> but not that of feathers in general, IMHO, which would have to be
> present _and_ quite long before this behaviour evolved.

To clarify: I never ever said that feathers FIRST evolved for drag.  
Insulation came first, and was most likely the primordial function of 
feathers.  Their "fluffy" structure pre-adapted them for drag, useful in 
gravity-assisted leaps (incipient parachuting).  Then the feathers on the 
forelimb and tail  became longer and stiffer and wider.  This design 
pre-adapted the symmetrical vaned feathers for lift.  The wing feathers then 
became asymmetrical.  Evolution of flight by successive exaptations.


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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