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Re: birds scales



>There is simply no principle in biology that states this.  SOME juvenal
>characters are equivalent to ancestral character states, but this does not
>mean at all that ANY juvenal character state must be.  Down may appear first
>for many functional reasons having to do with development - it may simply be
>more  adaptive for the type of thermoregulatory problems chicks face, or it
>may develop earlier because of energetic requirements in feather production,
>or because it acts as a stimulus of some sort to parents, or for any number
>of other reasons.  Juvenal animals are not simply suites of ancestral
>characters - they possess many characteristics that are derived adaptations
>to being a juvenile.  There are so many such characters (the egg-tooth, just
>to give one example) that a statement such as the one you make above simply
>cannot be justified.

Touche' (tooshay?).  My last one was on the weak side.

Then the real question here is which feathers came first.  Are there any
feathers which may represent the earliest type?  I hope no one is suggesting
that the flight feather was the first to appear!  If anything, the flight
feather is the most derived of the bunch.  The point I am entertaining is
the fact that down appears to be the most underived, this *suggests* that it
came first (although I'd be willing to consider any alternate ideas).  If
feathers appeared as an unique adaption to the problems of thermoregulation
(being a highly derived hair-like structure), then the finest, and simplest
feathers would represent the first ones to appear.  Besides, is there any
evidence to suggest that a feature (once formed) becomes less complex through
the life of the group?  It seems to me that the opposite is true.

Rob

***
"Don't panic!"