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Re: Sinosauropteryx tail colors



2010/1/28 Jura <pristichampsus@yahoo.com>:
> This is purely speculative, but if it was originally evolved for display, 
> then perhaps the display was that of a warning. Perhaps the animals used 
> these protofeathers as a way to appear larger to rivals, or to potential 
> predators.
> Of course this would require the subsequent presence of (proto)feather 
> erector muscles. Still, not entirely out of the question.

At least, there are muscles associated with the ventral scales in
snakes, and probably to the dorsal scales of crocodylians which move
the water on its back when mating, so I suppose that if they are also
present also in bird feathers, they would also be associated with
protofeathers.

>Alternatively, the protofeathers might have had a use analogous to the fur of 
>tarantulas, or the super wispy skin of some gecko species; in that they would 
>tear off easily, leaving predators with a mouth full of (possibly irritating) 
>fuzz.

I do not think the protofeathers to be irritant because this seems to
be just an apomorphy of certain spiders. As far as I know, no other
sauropsid has irritant epidermal structures.

Ringed tail signaling does not seem to require protofeathers, because
as said before, many non-avian sauropsids have similar patterns.
Protofeathers would make the tail just a little larger, and then more
obvious. The showing large issue seems as a reasonable adaptive
explanation.

Because of the evidence suggesting tachymetabolism, lately increased
with locomotion data, I would lean towards insulation, yet it is true
that we do not have evidence for a more complete coverage by
protofeathers (although independently inferred tachymetabolism would
suggest so). Anyway, new structures are originally formed
independently of adaptive function, and they are later conserved if
they are useful. And, there may be more than one reason for which a
feature like protofeathers was useful, and in such a case, both
advantages increased the fitness of the animal bearing them. It may be
hard to tell what one was more important if we do not have means of
rejecting one of the two alternatives.

Of course, they may have been preadaptive if they were not so
necessary for heat conservation (are there uninsulated tachymetabolic
animals of this size?) or if the animals did not payed attention to
the hair for display (do crocodiles pay attention to the scales of
their fellows, or just to the the way they move the water? - if not,
the EPB is ambiguous and does not give positive support to the display
hypothesis).