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Sankar's Pachy

I have seen the "pachy" briefly at SVP, very briefly. I was
supposed to go over the X-Rays and see it again at Florida
but, by the time I had time, it was under plexiglass and on
the display. So I hope to work with Sankar on it soonish, if
he's still interested. He has a tape of the CT, so I hope we
can convince Art Andersen to try and build a 3-D model of
it. Anyway, It is a big boss-like structure, nicely
preserved that, at least supericially, looks like it could
be a pachy, although that would throw us into  bit of a
temporal tizzy, although I enjoy a good tizzy now and then.
When I looked at it I did not see any evidence of a
braincase which I believe to be critical. Without it, the
specimen I saw could not be nailed down to be a dome. We do
have to avoid the potential problem with other boss-like and
ornamental structures that mimic domes. Majungatholus was a
problem pachy, in part because it was in an odd place
paleobiogeographically, and it had no braincase. It, of
course, turned out to be the big-old ornaments (paired) on
the face of a theropod. Even some bone ends can look a bit
domeish if preserved just right (or wrong). So a braincase
is real important. Sankar implied he had one, so I'm anxious
to see it.

Now, a braincase doesn't nail it down either because there
is variance in what dino braincases look like. Probably have
to get Emily B. to look at it and compare with various
dinosaur braincases to see if it looks like a pachy
braincase should look.

The options are many, including the Majungatholus and dome
scenarios above. There are also other organisms that have
had a habit of generating structures like this (e.g.
therapsids, although nothing so convex to my recollection -
Sankar's is pretty vaulted - his dome that is). That's why
accessory material is critical and we must remember that in
science, the more extreme the implication - such as the
temporal paradox here - the more solid the data has to be to
support it. If it was found in the UK of western North
America, it would probably be put in a box of misc. domes if
it didn't have a braincase. I think that's what Mark Goodwin
was implying with his comment. But it would still be a
less-supported assertion there as well and something else
could get in under the radar. Certainly, though, no one
knows a good dome better than Mark.

That also leads to comments on the Marginocephalia in
general. It is still alive but, I think, most of us with
ceratopsian or pachy interests would be hard-pressed to feel
all that confident it means much compared with the solidness
(probably a non-word) of the Pachycephalosauria and
Ceratopsia (depauperate in apomorphies of any strength). I
suspect the Marginocephalia will not live all that much
longer and that the basal ornithischian nature of early
pachys and such really suggests a different scenario will
win out, if good material from important areas and times
will come out eventually. 

Perhaps Sankar's "Pachy" is it. I'll keep an open mind and
will see what happens. What I saw in Denver was far from
enough to really convince me - but Sankar probably has lots
more data, so, again, we'll see. I also second any statement
about Sankar being a sharp individual. I think so. I was
very upset about the little disclaimer the editor of the
latest tome put in about his realizing the paper was
controversial and publishing it despite this. That wasn't
necessary. There was sufficient stuff in the paper to merit
publication and the editor just should hve done it without
throwing that in. All important/good papers have some
controversy, or just about all.

Anyway, should be an interesting time for us pachy types.
looking forward to the latest paper from Mark and John (aka
Jack Horner) - sounds pretty biblical to me.


Ralph E. Chapman
Applied Morphometrics Laboratory
National Museum of Natural history
ADP, EG-15  NHB, 10th & Constitution, NW
Smithsonian Institution
Washington, DC 20560-0136
(202) 786-2293, Fax: (202) 357-4122