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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

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

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

Nick Pharris



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).