RE: archie feathers

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Colin McHenry
>
> ----- Original Message -----
> From: "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>
>
> > Actually, no: there are yet more possibilities:
> > *Ontogenetic variation (after all, the feather IS smaller than the
> retrices
> > and remiges of the Archies with good feather impressions)
> > *Seasonal variation (although in modern avialians, such changes are
> > predominantly color-related)
> > *Taphonomic variation: the lone feather, after all, is preserved via
> > carbonization, while the others are through impressions.
> Furthermore, any
> > 2-dimensional (or nearly 2-D) representation is a 3-D object
> suffers from
> > distortions; the same object might produce one of several
> different forms
> > when projected onto a 2-D surface.
>
> Is the possibility that the isolated feather is a detached down or contour
> feather included in these?

Actually, that was one of the original points, to which my possibilities
were added.

> Paul Davis (1995)states that these feathers
> become detached from the carcass before the flight feathers (alluding to a
> system of decay stages that he details in a later publication - Davis &
> Briggs 1998).  Are there down or contour feathers preserved on any of the
> _Archaeopteryx_ specimens for comparison?  My impression has always been
> that the specimens show the impressions of the flight feathers only.

Correct: the body feathers are poorly (to not) preserved in _Archaeopteryx_
(and of course NO feathers are preserved in some specimens, which has
bearing on...)

> He also states that the _Compsognathus_ specimen from the
> Solnhofen "may for
> all taphonomic intents and purposes be treated as a small
> featherless bird"
> [p91].  The implication is that, if small dinosaurs like _Compsognathus_
> were feathered (as was its close relative _Sinosauropteryx_), why
> are there
> no feathers preserved on the Solnhofen _Compsognathus_, despite the famous
> frequent preservation of feathers in the limestone?

Actually, as I mentioned above, several _Archaeopteryx_ specimens lack
feather impressions, so just because the Solnhofen CAN preserve them doesn't
mean that it always did. Furthermore (and importantly), the _Compsognathus_
specimens seem to lack *any* preserved integumentary impressions (scales or
feathers), so the simplest explanation is that the particular
microenvironment in which those two skeletons sank were not the
microenvironments that preserve either carbonized or impressed integument.

> He doesn't
> specify what
> stage of decomposition the specimen is at, but it would seem possible that
> the specimen was preserved at a stage of decomposition after the
> loss of the
> integumentary structures.  In which case, if it is not a down or contour
> feather from _Archaeopteryx_, then might the lone feather be from
> _Compsognathus_?

That is certainly possible, although based on the known style of plumage in
_Sinosauropteryx_ that isolated feather would seem to be VERY advanced for
Compy.  And, of course, there would have been other coelurosaurs present in
the onshore environments, so it could be from these as well.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796