RE: SVP Preview

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Mickey Mortimer wrote:

> Untrue.  He states (in his 2002 SVP abstract) that Metriacanthosaurus is
> "more closely related to Allosauroidea" than to Spinosauroidea
> (containing megalosaurids).  

Then this clade should be called Megalosauroidea, shouldn't it?

Interestingly, Allain alludes to _Megalosaurus_ being a possible _nomen
dubium_, with the name restricted to the type dentary.  

And on the topic of sauropods...

> Titanosaurus? madagascariensis is a good example.  The holotype is not 
> nomen dubium, as Curry Rogers and Forster (2001) state parts come from 
> Rapetosaurus, and parts from the new saltasaurine.  One of the latter 
>taxa  should be kept as madagascariensis, the other given a new species 
> name.  Just because a specimen is composite doesn't mean the taxon 
> associated with it should be forgotten.  Anyway, the single caudal 
> vertebrae preserved in the T. madagascariensis holotype were diagnostic 
> enough to refer to the proper taxa, why not those that make up T. 
> indicus or T. blanfordi?  

Good question.  It all boils down to at what level the caudals are
diagnostic.  _T. madagascariensis_ has rather "blocky", square-shaped
caudals.  _T. blanfordi_ has long, cylindrical caudals (successive revisions
of this species have referred those caudals of different morphology to _T.
madagascariensis_).  _T indicus_ and _A. septentrionalis_ have tall and
laterally compresed ("flat-sided") caudal centra.

Now, the morphology of the caudal vertebrae is often sufficient to determine
what titanosaur taxa they *do not* belong to.  For example, the rather
blocky caudals of _T. madagasariensis_ are very different from the lower,
more dorsoventrally compressed caudals of saltasaurines.  However, this
"blocky" caudal morphology may not be unique to _T. madagascariensis_.  If
it is, then the species may be valid, and the Indian and Malagasy titanosaur
material can be referred to it.  However, the cylindrical caudals
"diagnostic" for _T. blanfordi_ are seen in other titanosaurs - e.g.
_Pelligrinisaurus_.  

_T. indicus_/_A. septentrionalis_ is a rather different mess - the validity
(or otherwise) of these species is something I'm looking in to.



Tim