Re: [Re: Origin of feathers]

[archosaur@usa.net]

owner-dinosaur@usc.edu wrote:
> In a message dated 98-04-08 03:39:27 EDT, jwoolf@erinet.com writes:
> 
> << Hence, a different thought: maybe feathers developed not as an organ
>  that _did_ something so much as an organ that _showed_ something --
>  i.e., a courtship or territorial display of some sort. >>
> 
> I still like the idea that pre-feathers appeared as a mechanism for excreting
> excess sulfates (see ref in prior post), because this provides a compelling
> rationale for their >initial< appearance. Pre-feathers >couldn't< appear
> initially >for< display or >for< flight, for example, since these functions
> didn't exist until the pre-feathers >had already appeared<. Only after the
> pre-feathers appeared could they start to acquire various other functions, and
> only then can natural selection act on them. 
 
While I can't (and won't) voutch for flight as a reason for the development of 
feathers, I can still see them arising for something such as mating. 

When looking at extant reptiles (mainly squamates) I can see many cases where 
scales have been modified for an attention getting purpose. I'm not just 
talking color either, but as attachments.
I can cite both Chlamydosaurs and the Pogonids for  examples. Both have scaly 
appendages that can be voluntarily erected. Chlamydosaurs have the large neck 
frill and Pogonids have the beard. If I'm correct Chlamydosaurs extend their 
frill using only the first ceratobranchials from the thyroid arch. Everything 
else is just reformed scales. Pogonids I believe don't use any bony branch 
whatsoever to lift their beards. Both lizards have reformed their scales to 
suit a very important (although some might say impractical) need. To make 
predators think twice about messing with them. I see no reason why 
Sinosauropteryx and other animals with protofeathers wouldn't use their 
feathers for the same reason. In fact I could have sworn that Ostrom himself 
stated that he believed that the feathers might have supported a crest of some 
sort. I tend to agree. 

As for mating. Well there are many reptiles today that use flashy means to get 
the attention of the opposite sex. One commonly seen group is the anolis. They 
use an extendable dewlap with a flashy color on it. The only purpose for that 
is to get a mate, well that and territory, but in their case it's basically the 
same thing.

What is a feather. To put it generally a feather is simply a modified scale. 
Why would an animal opt for something as light as feather for display purposes? 
Perhaps it had something to do with it's environment or it's lifestyle. Maybe 
the feather came about as an evolutionary accident turned advantage.

Either way it seems that their first purpose would be to attract attention. Be 
it for defense or a mate. Possibly both.

> The idea is that the creature doesn't say, "I need to fly and I need pretty
> colors, therefore I shall develop feathers." Rather, it is, "Hey, I've got
> feathers. Now I can start flying and showing off."

Something like that. Although it's probably more like "Now I can show off and 
oh look as an added advantage I can fly"
 
> Molting, incidentally, would be part of the excretory process, and is thus a
> good candidate for the oldest retained feature of avian feathers.

Is there that big a difference between a bird molting and a lizard (or snake) 
shedding? (Not my field)

Archosaur J


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