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Re: Another feather theory



On Wed, May 26th, 2010 at 2:25 AM, "Richard W. Travsky" <rtravsky@uwyo.edu> 
wrote:

> On Sun, 23 May 2010, Dann Pigdon wrote:
> > A 'feathery lure' would only evolve if it allowed the prey animal
> to 
> > escape often enough to justify such biologically expensive
> structures.
> 
> How does that compare to a detachable tail?

Tails were around long before they became detachable, and no doubt some of 
those 'non-
detachable' tails were torn off or severly injured by predators in flagrant 
disregard to their 
supposed 'non-detachable' status. Even worse, some of the more robust tails may 
have steadfastly 
refused to detach, resulting in the animal attached to them being betrayed by 
their own appendage.

If tails were being ripped off mercilessly anyway, then evolving a detaching 
mechanism that didn't 
result in excessive blood loss or infection would have been positively selected 
for. Even then, 
recent studies have shown that the regrown tails are far inferior to the 
originals, and that 
individuals that detach an original tail are severely disadvantaged for the 
rest of their life. Dropping 
a tail is a last-ditch attempt to avoid predation at any cost.

If the 'mouth full of feathers' analogy has evolved in a similar way (assuming 
it's even a distinct 
strategy that has faced selective pressure), then feathers would have had to 
exist *before* the 
strategy was selected for, thus making it an unlikely impetus for the *origin* 
of feathers.

> > You'd also expect very early feathered theropods to have quickly
> reduced 
> > the length of the bony tail while replacing it with increasingly 
> > elongated feathers, if feathers originally evolved as detachable
> lures. 
> > Perhaps there's a case for arguing such a strategy for Nomingia.

> Why would it have to be just tail feathers? An attack from the side with
> contact on the body could also result in a mouthful of feathers.

Yes - although detachable feathers close to the body pose a much greater risk 
of soft-tissue injury 
than long feathers sticking well out from the back of an animal. Also, those 
feathers would have 
had to be long enough to form a buffer *before* they were positively selected 
for as detachable 
escape mechanisms, again suggesting that predator avoidance was probably not 
the main impetus 
for the original development of feathers (although perhaps a useful secondary 
use).

-- 
_____________________________________________________________

Dann Pigdon
GIS Specialist                         Australian Dinosaurs
Melbourne, Australia               http://home.alphalink.com.au/~dannj
_____________________________________________________________