Coelurosaur skin (was Re: Jurassic Park)

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 11:46 AM 9/27/98 -0400, Jeff Poling wrote:

>   It's a real shame that this thread has come up while so many people are
>at SVP.  I know Dr. Holtz would have a few things to say about this.  Rather
>than making a clumsy attempt at explaining this on my own, I suggest reading
>"What is parsimony, anyway" in my Journal at http://www.dinosauria.com  The
>"hypothesis examples" are almost verbatim from Dr. Holtz.

Well, I AM still here, at least today (much to my students chagrin: first
test is in an hour and fifteen minutes...).

>   I should also add for the benefit of the person who was talking about
>bumpy, pebbly skin impressions being found for _Velociraptor_ (which is not
>true) and other theropods:  the impressions that are known are of large
>animals (is an elephant or hippo a good approximation of the hairiness of
>all mammals?) and, as Dr. Holtz once pointed out, the skin impressions were
>not preserved in sediments that would have preserved feathers (or their
>impressions) had they been present.

Another important point: at present, we do not have any definite preserved
integument of any non-avian coelurosaur except for _Sinosauropteryx_ and the
other Yixian forms, and the gular pouch of _Pelecanimimus_.  There is a
patch *associated* with a tyrannosaurid, but not *articulated* with it.

The preservation of skin structures is less-well preserved than normally
considered: for example, we don't have good evidence for the skin of any
_Compsognathus_ specimen, the body covering of _Archaeopteryx_ (wing & tail
feathers are fine, body covering not preserved), etc.  _Scipionyx_ doesn't
have preserved external structures, and most of the "integument" of
_Pelecanimimus_ is actually internal structures.

The three different possible cladograms presented in the _Caudipteryx_
papers placed _Protarchaeopteryx_ as: a) closer to _Caudi_ plus later birds
than to dromaeosaurids; b) closer to dromaeosaurids than to _Caudi_ plus
later birds; c) outside the dromaeosaurid-bird clade.  In either b or c the
*scientific* option (i.e., the one based on the most parsimonious
distribution of the evidence presented) is that dromaeosaurids were either
feathered or were themselves secondarily featherlessness.

Evidence to the contrary?  At present, lacking.  There are no skin
impressions (yet) of dromaeosaurids.  Claims that dromaeosaurids *must not*
have been feathered are not based on evidence: they are based on the
traditional perceptions and reconstructions.

What would it take to overturn the hypothesis that dromaeosaurids were
feathered?  Dromaeosaurid skin impressions, phylogenetic data placing them
outside all known feathered forms, etc.

And just two years ago, the evidence that dromaeosaurids were feathered was
equivocal (at best).  Ain't science wonderful?

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