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Re: Sinosauropteryx tail colors



--- On Thu, 1/28/10, Tim Williams <tijawi@yahoo.com> wrote:


> Don Ohmes <d_ohmes@yahoo.com>
> wrote:
> 
> > Not sure I disagree (although given my track record
> it
> > might seem likely), but wouldn't the more exact
> analogy be
> > claiming that bone itself evolved as a "display
> mechanism"?

> I wouldn't have thought so.  It's the selection
> pressure that's common here, not the mechanism by which
> structures are engendered.

Fair enough, I suppose. The point that the abundant 'display pressure' that 
theropod brains apparently created needed material to shape, and further, such 
material likely had pre-existing function is still relevant, though. 

Benton seems to be saying in the press release* that the very first wisps were 
irresistibly attractive to the ladies, and/or overwhelmingly intimidating to 
reproductive rivals, prior to any other function. Given that partial feathering 
(eg, a midline "crest") can protect skin from sun, have a concealing effect, or 
even be secondary, that argument seems quite a stretch. 

I think the argument that the large size, vanes, and coherent flat surfaces 
needed for aerodynamic effect were initially the result of visually-based 
intra-specific selection on pre-existing structures of unknown function is 
inherently more rigorous than any argument that excludes the possibility of 
some underlying function(s) performed by those structures. 

The specific analogy drawn by M. Erickson that the argument as it appears in 
the PR is analogous to finding color in zebra hair (or deer, or whatever), and 
then claiming to have proved a 'display origin' for fur seems apt, to me.

That said, the argument that "display function preceded aerodynamic function" 
indeed seems stronger than ever. But then, it was always strong from a logical 
perspective.

*"We therefore suggest that feathers first arose as agents for colour display 
and only later in their evolutionary history did they become useful for flight 
and insulation." -- Benton as quoted in the article linked below...

<http://www.scienceda