Re: Shuvosaurus

["Mickey Mortimer" <Mickey_Mortimer11@msn.com>]

George Olshevsky wrote-

>Incidentally, I still have Shuvosaurus as a non-dinosaurian archosaur. How
>serious is this idea that it is a toothless coelophysoid theropod?

Very.  The only reason Shuvosaurus was evwen removed from the Theropoda in
the first place was because Long and Murry (1995) thought Chatterjee didn't
prove it was a theropod.  They figured since no toothless Triassic theropods
were known, it was more likely to be the head of Chatterjeeia, as Lotosaurus
lacks teeth.  Rauhut proved it was theropod- "Shuvosaurus differs from
rauisuchians and other basal crurotarsans in the following characters: loss
of the postfrontal, paroccipital process directed ventro-laterally, lacrimal
dorso-ventrally elongated, inverted L-shaped and exposed on the skull roof,
presence of a deep basisphenoid recess, and ectopterygoid with expanded
medial part and deep ventral fossa. All of these characters are found in
theropods, and the latter three probably represent synapomorphies for this
group (Gauthier 1986); therefore, Shuvosaurus can be referred to the
Theropoda."  So get it back on that list. :-)

Rob Gay wrote-
> Are the associated teeth coelophysoid though?

Then Tim Williams wrote-
>Apparently not (although I believe Carpenter [1997] described the tooth as
>coelophysoid).

Rauhut's statement is simply indicating that as crurotarsan and basal
theropod teeth are similar, it is difficult to tell which the Gojirasaurus
tooth belongs to.  As usual, I think closer examination will show
differences between crurotarsan and theropod teeth, but in any case, the
tooth of Gojirasaurus is distinctive.  It has a root, so was not shed by a
scavenger.  There are blood grooves, as in tyrannosaurids and troodontids.
Also, the posterior serrations curve towards the tip, as in segnosaurs,
troodontids and "velociraptorines".  The serrations are not enlarged and the
anterior serrations are equal in size to the posterior serrations, unlike
those coelurosaur groups.  I think this indicates a basal theropod was
paralleling derived coelurosaurs in tooth morphology.  It differs from
Coelophysis and Liliensternus, but there are no dental characters known that
could distinguish a coelophysoid tooth.

> >But, the type material for _Shuvosaurus_ may be juvenile,<
> I don't remember Chatterjee mentioning a lack of fusion, but I'll re-read
> the original paper (has anything else been published between then and this
> recent thesis dealing with this animal?).

Read- http://blackwidow.informatics.sunysb.edu/anatsci/files/Rauhut_97.doc .
Rauhut writes- "Judged by the well visible and sometimes even open sutures,
the holotype represents a juvenile individual, despite its rather large size
of c. 170 mm."

> That seems like a fairly distinctive element. How much larger? (Apparently
> large enough to say it may be _Gojirasaurus_). What about the other
elements
> assigned to _Gojirasaurus_?

The large premaxilla is 38 mm long, the holotype premaxilla is about 26 mm
long.  So about 46% larger.

Mickey Mortimer