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Re: Pterosaur feathers?



George Olshevsky (Dinogeorge@aol.com) wrote:

<Those aren't scales, even though they look like scales. As far as I know,
feathers and croc scutes, and thus by phyletic bracketing dinosaur dermal 
structures, are not homologous with lepidosaur scales, just as they're not
homologous with mammal hair.>

  How odd. Referencing work of herpetologists like Al Romer, and more
recent (below), the histological and chemical work says they're scales,
but I guess since phgylogenentic bracketing puts feathers somewhere inside
a clade that one outgroup has identical tubercular structures that are
keratinous, squamose, and are essentially chemically identical to
lepidosaurian scales to those of helodermatids (lepidosaurians) which are
also tubercular. Phylogenetically bracketed, archosaurs and lepidosaurs
are reptiles which are characterized by the pappilary origin of their
epidermal structures, something that the dermal scutes of crocs and
various dinosaurian clades are not homologous to. The keratin is, but not
the bone.

  Morphological analyses point to archosaurian scales, such as birds and
crocs, which have identical form, condition of alpha and beta keratins,
and origns.

  You can reference data from:

  http://www.uta.edu/biology/restricted/3452int.htm

  and

  faculty.washington.edu/kepeter/ 453/lectures/tetrapod-skin.htm

  in which the details are explained. Researche by Chinsamy and others,
the SUNYSB team and Chinsamy, etc., are working or have published and
permitted assessement of the chemical nature of bird scales and croc
scales. And that yes, as any herpetologist will tell you, however you may
personally disagree, they are scales.

  I would like to see what personally lends you (George) to saying that
"Those aren't scales, even though they look like scales." It would help me
in understanding where you are coming from.

  Some refs for fun:

Schweitzer, M.H.; Watt, J.A.; Forster, C.A.; Norell, M.A.; & Chiappe, L.M.
1997. Keratinous structures preserved with two Late Cretaceous avian
theropods from Madagascar and Mongolia. _Journal of Vertebrate
Paleontology_ 17 (supp. to 3): 74A.

Schweitzer, M.H.; Watt, J.A.; Avci, R.; Knapp, L.; Chiappe, L.M.; Norell,
M.A.; & Marshall, M. 1999.  Beta-keratin specific immunological reactivity
in feather-like structures of the Cretaceous alvarezsaurid, *Shuvuuia
deserti*. _Journal of Experimental Zoology_ (_Molecular Developmental
Evolution_) 285: 146-157.

Schweitzer, M.H.; Watt, J.A.; Avci, R.; Forster, C.A.; Krause, D.W.;
Knapp, L.; Rogers, R.R.; Beech, I.; & Marshall, M. 1999. Keratin
immunoreactivity in the Late Cretaceous bird *Rahonavis ostromi*. _Journal
of Vertebrate Paleontology_ 19(4): 712-722.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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