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Re: Scales, hair, integumentary structure relationships?
Why couldn't you have scales and hair side by side if they were homologous?
If rat tail scales are not homologous to reptile scales, then that would seem
to invalidate the argument that hair could not be homologous to reptile scales
because they both appear in the same area
> > In mammals, the scales are composed of agglutinated
> Oh! That's a very good argument.
So the rat tail scales are homologous to rat hair? so why couldn't you have
hair and reptile scales side by side without them being homologous?
What mamalian scales are we refering too? rat tails, the banded armadillo
shells, porcupine quills? finger nails?
I seem to remember reading about an armadillo like armored prehistoric mammal -
> >> btw Molecular biology is what I studied in
> college, not
> >> palentology.
> I've studied both. :-)
Well, I've had no formal palentology instruction, basically, I'm saying forgive
my lack of knowledge on the intricacies of all these structures, I'm still
trying to sort out where these structures appear on the cladogram, and what is
> >> I wonder what value there would be to looking at
> >> various alpha- and beta- keratin sequences, and
> try to
> >> determine a rough time frame for their divergence
> (does it
> >> roughly co-incide with the synapsid/reptile
> You mean the one between Î and Î? That one ought to have
> happened a little
> later, but not much later.
Well, i would assume (possibly incorrectly) the first reptile scales had just
alpha keratin, and beta was later added to harden them. If the last common
ancestor of synapsids and diapsids had a structure that became both hair and
scales, then i would expect to see beta keratin appear earlier, possibly right
at the split - perhaps beta keratin allowed the structure to form effective
Too much speculation I suppose
> What I didn't mention is that only the dorsal scales
> were lost! The ventral
> ones are the gastralia.
gastralia are only found in reptiles right? mostly archosaurs right?
Is this an atavism? or did synapsids and true amphibians loose them
On that topic- the bony scutes of crocodiles, phytosaurs, the dermal plates on
saltasaurus, etc - could they be atavism's of dermal orgin bony fish scales?
(genetic evidence would be nice here, since we have living examples)
> >> seyomouria juveniles were found with scales, but not the adults - and
> >> they were clearly terrestrial
> Where? The Seymouriamorpha page doesn't mention this,
> and the *Seymouria*
> page says "No scales have been found, but this could
> be an artifact of
Sorry, I was just going off memory, it was a Seymouriamorpha:
"Larval specimens of Ariekanerpeton had circular scales with concentric rings
similar to those found in Discosauriscus, but postmetamorphic specimens appear
to have lost them."
> What do you mean -- the existence of a larval stage with
> external gills, or
> the metamorphosis proper (a drastic concentration of the
> changes into a short interval, as opposed to having them
> spread out between
> hatching and maturity)? The latter has so far only been
> found in
> lissamphibians and to a lesser degree in a few
> temnospondyls like
> *Amphibamus* and *Apateon*; the former is the usual state
> of affairs and
> only known to be absent in amniotes and a few
I guess I mean the type found in lissamphibians. I think I didn't ask a very
good question, I don't suppose there is really a clear distinction between what
is "metamorphasis" such as seen in amphibians, and "maturation" like mammals
(would puberty and such be considered metamorphasis - hair grows where it
didn't before, whereas in amphibians, legs grow where they didn't before..)
never mind, I retract my question.