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RE: Sinosauropteryx protofeathers

At 03:44 PM 1/21/99 -0800, Dwight Stewart wrote:
>Okay, I know I'm asking for a verbal spanking here, but HERE GOES:
>will someone give a clear definition of "protofeather" as contrasted to

Yeah, that's a good question.

Some facts, first:
A) We do not *AT THIS TIME* know much about the structure of the
integumentary fibers of _Sinosauropteryx_.  In fact, that would be the
safest thing to call them: integumentary fibres.  Not feathers, not
protofeathers, etc.

B) There is a bigger diversity of feathers than you think there is.  (This
statement holds true even for ornithologists, some of whom were impressed by
feather diverstiy as shown at the Feathers Origin meeting).  We have to
remember that "feather" *does not equal* "flight feather".  Feathers also
include natal down, adult down, contour feathers, barbs, eyelashs,
filoplumes, etc., etc.  (There was some debate at the Feathers Origin
meeting as to whether or not the funny tuft of hair-like integument coming
out of the chest of male turkeys were feathers or not).

C) General agreement about modern feathers: regardless of the morphology
produced by development, they all start from circular follicles, and they
all have a similar (and highly specialized) keratinous composition.

So, are what's on _Sinosauropteryx_ homologous to feathers?

WE  -  DON'T  - KNOW  -  YET.

There *ARE* possible tests in terms of morphology and chemistry which will
probably solve this problem.  Some of the these tests are under way. The
results have not been published.

So, everybody, deal with it.  We don't know yet.

>Here's what I'm fishing for: are there defined characteristics that would
>identify a structure AS a protofeather (as opposed to a feather).  I know
>this has been hit on before, BUT - is there some characteristic and/or
>structure of
>a feather that DEFINES it as a "true" feather?

Funny, sounds like a good topic for a symposium... :-)

One thing to remember, too, is that like the tetrapod limb, feathers almost
certainly didn't just spring out of nowhere, but instead will we find that
there are a series of early forms which we would be hard pressed to state
are clearly "feathers" or not (even if they were clearly feather
homologues).  By the same token, the fins of various fish groups grade
through the basalmost tetrapods before becoming typical tetrapod fins.

Evolution happens.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661