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M&M's ;)



Hi all,

Everyone had a great time at the SVP? I am still planning on going to one
someday, but here's another thing:

When reading through the "Problematic Theropoda "Carnosaurs"" chapter in the
Dinosauria, I came across the short description for _Marshosaurus_ which
reminded me of another genus. For those who don't own the book (shame on
you! =)), here's a partial segment and the most important one that is:

"The taxonomic position of _Marshosaurus bicentesimus_ is unclear. The ilium
appears to have a narrow brevis shelf as in carnosaurs, while the pubic
shaft is bowed cranially as in ceratosaurus. That this pubis does pertain to
this species is confirmed by the match of the convexities of its(?) iliac
articular face to the concavities of the pubic articular face of the ilium.
Furthermore, the pubis otherwise resembles that of _Coelurus agilis_.
_Marshosaurus_ cannot be considered a carnosaur."

When looking at the pubis of _Coelurus agilis_ in the same book at page 288,
assuming that it is resembling the one found in _Marshosaurus_, the shape
reminded me of another genus, the second "M" so to say. The second "M" is:
_Monolophosaurus_.  The partial reconstruction seen in "The Scientific
American Book of Dinosaurs", done by our beloved HP Greg Paul, shows indeed
a near identical pubic morphology as the one seen in _Coelurus_, giving a
piece of evidence that _Marshosaurus_ should be grouped with
_Monolophosaurus_ as a relative to the former.

But wait, there's more, you can't base such a supposed phylogenetic
relationship based on just a single character that is due to be part of
convergent evolution (as the same pubic morphology is also found in
_Coelurus_) On the AMNH website (http://paleo.amnh.org) there is an image of
a referred dentary to _Marshosaurus_ (reasons unknown, it just is) which is
in some ways similair to the one found in _Carnotaurus_ but this is just the
fact that both are curved. When looking at the image, there is a distinct
curvature between the surangular articulating surface and the tip of the
dentary which is also seen in HP Greg Paul's skeletal reconstruction for
_Monolophosaurus_. There are some minor differences however, one being that
the dentary in _Marshosaurus_ is proportionally shorter than that is found
in _Monolophosaurus_ and somewhat deeper, but on overall morhology they are
very similair.

As the dentary curvature is also seen in _Carnotaurus_ and many other
carnosaurian genera, they do not exhibit the lower angle relatively between
the tip of the dentary and the remainder of the dentary itself, which is in
the two genera comparable and the curvature is more placed near the tip of
the dentary in _Marshosaurus_ and _Monolophosaurus_ relatively when being
compared to the dentary in _Giganotosaurus_ for example. As both features
are liable to be convergencent evolution one should not at both seperately,
they come out much better when viewed in association. The latter is found in
the M&M's which exhibit both of these features. Unfortunately cranial
material is not known for _Coelurus_, or else better comparisons could be
made which would have had more certainty.

A second "but"...

But could someone please, please, please send me figures of the publication
which describes the two other previously unidentified _Marshosaurus
bicentesimus_ specimens and some of the figures in the _Monolophosaurus_
paper? That way I can make better comparisons between these genera, as well
as others,  that are more reliable than just these two based on poor
material. Many thanks in advance!

Cheers,

Rutger Jansma