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Re: feather tracts


Tim,
    Growth in tracts on the dorsal side is apparently advantageous and is
rarely lost.  Therefore I would expect this trait in the vast majority of
birds, dino-birds, and even their secondarily flightless descendants.
Whereas I would assume the growth of feathers on the ventral side could go
either way.
    Anyway, I think it will probably prove to have great evolutionary
significance, but we obviously won't be able to assess that anytime in the
near future.  In any case, I still believe that feathers started in one
region of the body and spread, and did not sprout up as whole body covering
(for insulation or any other reason).  Someday we will have Triassic fossils
that will shed light on these questions.
                   -----Ken
********************************************************

From: "Tim Williams" <twilliams_alpha@hotmail.com>
Reply-To: twilliams_alpha@hotmail.com
To: dinosaur@usc.edu
Subject: Re: feather tracts
Date: Wed, 11 Jul 2001 17:57:15 -0500


Ken Kinman wrote:

     The aerodynamic function was undoubtedly the last major exaptation.
Before that was insulation.  But the tendency of feathers to grow in
tracts
would indicate some function even before the insulation phase.


But do we know that the feathers of theropods like _Microraptor_ and
_Beipiaosaurus_ and _Sinosauropteryx_ *did* grow in tracts?

Besides, even if you are correct, the growth and arrangement of feathers in
tracts may reflect a developmental trait, and may have no evolutionary
(i.e.
selective) significance whatsoever.


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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