Re: Marshosaurus

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Jaime Headden wrote-

> 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.

Indeed they do, but no non-coelurosaur group has all of them.  You must look
at the entirity of the evidence, not pick each apart as if it were the only
supporting character.

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

Coelophysoids lack any sort of pubic boot, but yes basal aveopods and even
some non-coelurosaurian tetanurines (eg. Yangchuanosaurus) exhibit this
character.

>   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*.

Magnosaurus has a groove (Waldman, 1974), but you've yet to show me evidence
it contained a row of foramina.  Majungatholus does not have a well-defined
groove (Sampson et al., 1998), instead there is a wide longitudinal
depression.  No groove is present in Torvosaurus (Britt, 1991) or
Monolophosaurus (Zhao and Currie, 1994). Unfortunately, I lack a good figure
of Coelophysis' skull.  You're right regarding Carnotaurus, Giganotosaurus
and Baryonyx though.

>   *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.

Just because a character has been found to be polymorphic in a specimen does
not mean it is any less useful phylogenetically.

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

You're right regarding Masiakasaurus and Eoraptor (might as well just add
sauropodomorphs and ornithischians to the list if you're citing the latter).
What is your reference regarding small coelophysid teeth with basal
constriction?

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

I see no evidence in Sampson et al. (2001) that Masiakasaurus' teeth have
anterior serrations restricted to the distal half.  Indeed, one tooth
figured unambiguously lacks this character.  Although the teeth of Baryonyx
have serrations too small to see in the figures of Charig and Milner (1997),
they do not describe the condition seen in Marshosaurus or basal
coelurosaurs.

> 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*,

.... and oviraptorosaurs, Confuciusornis sanctus and Jeholornis.  It doesn't
matter where the disparate groups who evolved this character are
phylogenetically, it's obviously not useful for arguing against a
coelurosaurian relationship (unless you think Marshosaurus is a
"monolophosaurid" or spinosaurid).

> no supracetabular crest overhang,

Actually, it has a well developed supracetabular crest.  Which is expected
of any non-tyrannosaurid, non-maniraptoran theropod.

> a thick and not triangular ischiadic peduncle of the ilium

As in basal coelurosaurs like Sinosauropteryx and Ornitholestes.

> no vertical iliac crest between branches of the m. iliofemoralis

Like most theropods, including most coelurosaurs.

> an ischium with a dorsal projection from the lateral surface at midshaft

Looks like distortion to me, but which non-coelurosaurs do you think have
this character?

> broad boot-like ischiadic foot, rather than something more round

Oh, come on.  "Broad boot-like"?  The anterior margin is unpreserved, but
it's not very different from Compsognathus (corralestris specimen) or
Scipionyx.

> sigmoid pubic curvature

Like Coelurus, Compsognathus (corralestris specimen again) and the Santana
compsognathid?

> 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.

There is no evidence at all that an obturator foramen was present.  There
may have been an obturator flange or quadrangular process, but which is
present is uncertain.  The Santana compsognathid has both, and
Sinosauropteryx has the latter, so it is not a problem for a coelurosauria
identity.

> Many of these features are found in basal tetanurines, including a
> great deal of similarity to *Monolophosaurus jiangi*.

The only derived characters you've listed that are shored between the two
are- anteriorly expanded dentary; anteriorly reduced pubic foot; sigmoid
pubic shaft.  You'll note that Monolophosaurus actually has the triangular
ischial peduncle you seem to use as a coelurosaurian synapomorphy.

> The maxilla has
> distinct interdental plates, as does the dentary, but this may not be of
> any material value in a diagnostic analysis.

Indeed.  It was pointless to mention them.

In any case, I did not say that Marshosaurus was definitely coelurosaurian.
I said it was possible, and supported by the one phylogenetic analysis that
has included the taxon (Holtz's).  Or at least it was last year, I don't
know about his latest runs.  The new partial skeleton (Chure et al., 1993,
1997) will undoubtedly affect these opinions.  Maybe the cranial elements
and pelvis of Marshosaurus don't even belong together, I don't think either
was preserved in the new skeleton (so maybe it isn't even of Marshosaurus).
In particular the cranial elements suggest a deinonychosaur, while the
pelvis suggests a very basal coelurosaur like the Santana compsognathid or
Scipionyx.  A basal carnosaur like Monolophosaurus isn't out of the
question.  But the cranial portions have characters unknown in
non-coelurosaurian taxa.

Mickey Mortimer