Re: SVP DINO-PRESENTATIONS: _Stegosaurus_ vs. _Sinosauropteryx_

["Gigi Babcock or Ralph Miller III" <gbabcock@best.com>]

Pete Buchholtz wrote:

> Additionally, he (referring to Stephen Czerkas) insisted that the
(_Stegosaurus_ 
>tail) spikes were held up at about 50 degrees instead of near-horizontal.
 
Jeff Martz wrote:

> Same question here; Ken Carpenter played around with real stegosaur
> spikes and tail vertebrae when putting the DMNH stegosaur mount together
> and came to a very different conclusion.

Stephen Czerkas has played around with "real" stegosaur spikes and caudal
vertebrae, too, and reached an interpretation of his own.  At his talk,
Czerkas pointed out that, although these spikes are sometimes preserved in
the now-familiar flattened, posteriolateral horizontal orientation (as seen
in the DMNH 2818 specimen), other specimens preserve the pairs of spikes
one atop the other -- suggesting paired vertical tail spikes.  Czerkas then
presented a simple diagram suggesting how either orientation might
logically result if the "50 degree" above horizontal position were the case
for the living animal.  The ultimate appearance of the fossil spikes would
depend on whether the stegosaur tail was in the normal position or on its
side when it (along with the spikes) was buried and flattened.  Burial in
the "normal" pose would flatten the spikes down to both sides of the caudal
vertebrae; burial on its side would result in the one pair of spikes lying
atop the other pair.

On the subject of _Stegosaur_ plates, Czerkas pointed out that even if the
base of the plates emanated directly from the midline of _Stegosaurus_,
some amount of each plate (the "root," I might call it) would be buried
beneath the skin, resulting in some gap between the plates on the exterior
of the animal.  But, as Pete Buchholtz has already stated, Czerkas
interprets _Stegosaurus_ as having perhaps some lateral spacing between the
bases of the plates as well (in contrast to his earlier position on the
subject: see _Dinosaurs: A Global View_, page 142).     

Czerkas' graphic comparison of the dentary of _Stegosaurus_ and that of a
modern turtle (employed to illustrate why the restoration of stegosaurs
with cheeks wasn't supported by stegosaur jaw anatomy) presented a
persuasive argument.  He went on to recommend a reevaluation of
hypothetical cheeks on all ornithischian dinosaurs.  I'm all for careful
reconstruction of extinct animals, but I think that a good case can be made
for ornithopods and ceratopians (at least) having cheeks based on
comparative anatomy between these animals and extant herbivores.

Back to the drawing board, paleoartists!

On _Sinosauropteryx_: I was most interested in Philip Currie's
presentation, which revealed important new information on the three
fossilized individuals which he examined personally on three trips to China
in the past year.  Yes, you could say that he has a stake in the fossils
revealing protofeathers (just look at the two furry _Sinosauropteryx_
individuals on the cover of his _Encyclopedia of Dinosaurs_), but he
presented valid preliminary evidence to back up his interpretation.  As
Alan Brush has stated, the fibers do not show an anatomy comparable to
modern feathers, but I believe that these structures may indicate a
transitional stage unlike anything seen in extant birds.  Overall, the SVP
attendees seemed to respond favorably to Philip Currie's brief presentation
(I swear, he had to talk a mile a minute to pack it into the allotted
time).  But Larry Martin was clearly not swayed to see these fibers as
being related to feathers.  Perhaps the upcoming paper in _Nature_ (coming
around Christmas according to Mr. Currie) will yield more information.

The above post represents only my impressions of the statements made by the
above-named individuals, and may be inaccurate.  If any of the above
misrepresents the findings or interpretations of the above scientists, the
fault is mine and I apologize.  I thank the participating scientists for
putting forth their best efforts to research and present the latest in
dinosaur science.

Ralph Miller III (gbabcock@best.com>