Re: Marshosaurus

["Jaime A. Headden" <qilongia@yahoo.com>]

Mickey Mortimer (Mickey_mortimer111@msn.com) wrote:

<Characters found in coelurosaurs that I see include the constricted tooth
roots, a lateral dentary groove containing foramina, posterior serrations
much larger than anterior serrations, serrations on anterior carinae
restricted to distal half of tooth, reduced anterior pubic foot, open
obturator notch in pubis and ischium 2/3 the length of the pubis...>

  Though *Marshosaurus* possesses these, I would like to offer that some
of them have a much greater distribution than is found in coelurosaurs.

  A reduced pubic boot cranially is found also in "ceratosaurs"
(*Dilophosaurus*, *Coelophysis*, abelisaurids....).

  The lateral dentary groove which contains foramina is found similarly in
*Magnosaurus nethercombensis*, *Majungatholus atopus*, *Carnotaurus
sastrei*, *Giganotosaurus carolinii*, *Baryonyx walkeri*, and *Torvosaurus
tanneri*; the caudal margin of the jaw of *Coelophysis bauri* also appears
to have a groove in which several foramina reside, as it does in
*Monolophosaurus jiangi*.

  *Allosaurus fragilis* has an open pubic obturator notch. This does,
however, appear to be a convergence. Variability in opening of the notch
may be plastic, as indicated in the "compsognathid" described by Kellner
and Campos from the Santana Formation of the Chapada do Araripe, Brazil.

  Constricted roots are present in *Masiakasaurus knopfleri*, small
*Coelophysis bauri* and *"Megapnosaurus" rhodesiensis* teeth, and
*Eoraptor lunensis*.

  Similarly, restricted denticulation of the mesial carina are present in
some "ceratosaurs", including *Masiakasaurus knopferli*, and, if I'm not
mistaken, *Baryonyx walkeri*.

  Many of these features show the plasticity of some features, and I've
talked about variability of teeth. It is interesting to see many very
curious things in *Marshosaurus*. I am in amazement by this most
interesting Morrison theropod. There are, however, several features that
denote a less than coelurosauru relationship, including the dorsoventral
expansion of the symphysis as in spinosaurs and *Monolophosaurus jiangi*,
no supracetabular crest overhang, a thick and not triangular ischiadic
peduncle of the ilium, no vertical iliac crest between branches of the m.
iliofemoralis, an ischium with a dorsal projection from the lateral
surface at midshaft, broad boot-like ischiadic foot, rather than something
more round, sigmoid pubic curvature, and apparently a closed ischiadic
foramen, as the morphology of the puboischiadic plate in that area shows
distinct fracture and a suggestion of a complete obturator ischiadic
plate. Many of these features are found in basal tetanurines, including a
great deal of similarity to *Monolophosaurus jiangi*. The maxilla has
distinct interdental plates, as does the dentary, but this may not be of
any material value in a diagnostic analysis. Fused interdental plates are
present in a multitude of theropods (abelisaurids, some allosauroids,
spinosaurids, *Torvosaurus*, *Fukuiraptor*, tyrannosaurids, and
dromaeosaurids. Therefore, their lack of fusion would be as similarly
distributed in the other theropods, including coelophysoids,
*Herrerasaurus*, many carnosaurs, *Monolophosaurus*, "megalosaurids", and
several sundry coelurosaurs, but also disappear entirely in others.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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