Marshosaurus

[NJPharris@aol.com]

Hey, there.

You never know what you'll find rummaging through old books.  As I was
rummaging through Donald Glut's _The Complete Dinosaur Dictionary_ (1982), I
stumbled upon a copy of J.H. Madsen's drawing of the pelvis of _Marshosaurus_
(pg. 169).  I had never seen this animal illustrated before, so if no one
minds, I would like to take this opportunity to throw in my two cents
w/respect to this creature.

The ilium is classically allosauroid, with nearly parallel upper and lower
borders, a prominent supraacetabular ridge, and a long, thick,
forwardly-projecting pubic peduncle.

The pubis is long and slender, like that of _Sinraptor_ (Currie and Zhao,
1993, pg. 2068).  It is also strongly bowed (concave down and back).  In this
respect it is rather like the pubis of _Coelurus_ (_The Dinosauria_, pg.
288).  _Siamotyrannus_, a probable sinraptorid, also shows a slight bowing of
the pubis, but it is nowhere near as pronounced (Buffetaut et al., 1996, pg.
690).  The boot is much like that of _Sinraptor_ and also somewhat like those
of _Siamotyrannus_ and _Allosaurus_.

The obturator notch in the pubis of _M. bicentesimus_ is rather more open
(and _Allosaurus_-like) than in known sinraptorids.  Nevertheless this
species does retain a small nubbin of bone anteriorly (as in _Siamotyrannus_)
and a somewhat larger hook posteriorly bounding the notch.

The ischium compares very favorably to _Allosaurus_, having a triangular base
and a prominent, proximally-placed obturator flange.  As in _Allosaurus_, the
ischiadic rod is long, straight, slender, and flared distally.  In this
respect it is rather more like the ischium of _Allosaurus_ than like those of
sinraptorids, which are broader and bear a hook at the end.

Taking all of this together, I would place _Marshosaurus bicentesimus_ in the
Allosauroidea, above the Sinraptoridae on the line leading towards
_Allosaurus_.

Theropod pelves are far more diagnostic than most people give them credit
for!

Thanks for your time (assuming you're still reading)!

Nick Pharris

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Refs.:

Buffetaut, Eric, Varavudh Suteethorn, and Halyan Tong.  "The earliest known
tyrannosaur from the Lower Cretaceous of Thailand".  _Nature_.  June 20,
1996, pp. 689-691.

Currie, Philip J., and Zhao Xi-Jin.  "A new carnosaur (Dinosauria, Theropoda)
from the Jurassic of Xinjiang, People's Republic of China".  _Canadian
Journal of Earth Sciences_.  vol. 30, nos. 10 & 11, pp. 2037-2081.

Glut, Donald F.  _The Complete Dinosaur Dictionary_.  New York:  Carol
Pulblishing Group (1992).  [Originally published as _The New Dinosaur
Dictionary_ (1982)]

Weishampel, David B., Peter Dodson, and Halszka Osmo'lska, eds.  _The
Dinosauria_.  University of California Press (1990).