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Re: FEATHERS



[Oops...  In a message from Jeff Martz I attributed the following
 quote to George Olshevsky.  Looking at the records I see that it was
 Darren Naish that wrote it.  Please don't blame Jeff, and George and
 Darren please accept my apologies.  -- MR ]

On Thu, 3 Oct 1996, Darren Naish wrote:

> With re to the 'feathers evolved as insulators' thread..
> 
> Feathers are the most complex structure to have grown out of vertebrate skin
> _ever_. To argue that this structure _just happens_ to have been, later on,
> usefully exapted for flight is illogical. The only way to explain the initial
> appearance of feathers is to say that they evolved for aerodynamic purposes.  

        Which is simply ridiculous. Not the proposal, but that it is the
"only way". Everybody here should know that feathers are unsurpassed as
insulatory structures. To use George's argument, if they're so wonderfully
adapted for insulation, why argue they evolved for something else? 
        The counter-argument is, of course, "no other structure has ever
evolved for insulation that resembles the feather." Everyone should also
realize that this argument is as hollow and useless as the "no other
structure has ever evolved for flight..." argument. Has anything ever
evolved like feathers ever in the animal kingdom?
        Also note that while in the long term they've paid off
wonderfully, feathers in their initial form would seem less likely to win
out over other strategies like skin wings, in the short term. The presence
of insulatory feathers could resolve this problem. 
        I would not propose that anything as elegant as modern body
contour feathers evolved in any group of dinosaurs, but consider that they
may have started out as hairlike structures, then later evolved the side
branches, and finally the second system of branches on the individual
barbs, each of which would serve better to trap and hold air.
The actual appearance would probably be like the kiwi's furlike coat.
Evolution to flight structures would be something like what is noted
with mammalian hair in the sakis and the tail of the feathertail glider-
the ratite-like insulatory feathers would become gradually stiffer,
longer, more densely packed with barbs to better glide, maneuver,
etc. A major advantage of this idea is that it provides plenty of
intermediates, each of which would be fully functional in its own right
(right up to that  point where we have to figure out how to go to
powered flight, at least) Also the evolution of a complex structure (the
flight feather) froma simpler structure (ratite-like insulatory feather)
can be seen as  more parsimonious than the evolution of the complex
structure first. 

        Nick L.