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Re: Abydosaurus mcintoshi, a new sauropod from the Albian of Utah

GSP1954@aol.com <GSP1954@aol.com> wrote:

> Nemegtosaurus is known from plenty of postcranial material,
> its known as Opisthocoelocaudia. 

Although _Nemegtosaurus_ and _Opisthocoelocaudia_ were both found in the Nemegt 
Formation of southern Mongolia, they were found at separate sites that are 
several kilometers apart (Nemegt Uul and Altan Uul IV, respectively).

The skull of _Quaesitosaurus_ (another titanosaur) was also found in the Nemegt 
Formation of southern Mongolia, at a third site.  I know there is some talk 
that _Quaesitosaurus_ might be the same as _Nemegtosaurus_, but Wilson (2005) 
found enough cranial differences to separate the two.  There is also 
potentially a fourth sauropod taxon from the Nemegt Formation, known from a 
dorsal series (mentioned in Wilson, 2005).

So at this stage it seems premature to combine _Nemegtosaurus_ and 
_Opisthocoelocaudia_ into a single taxon.  This will have to await the 
discovery of associated cranial and postcranial material that can confirm or 
refute this hypothesis.  Until that happens, it's probably very dangerous to 
treat _Nemegtosaurus_ and _Opisthocoelocaudia_ as the same OTU.

> Funny how they often end up widely separated on cladograms. 

This is only funny (and then only mildly so) if _Nemegtosaurus_ and 
_Opisthocoelocaudia_ turn out to be the same titanosaur.  But this synonymy has 
yet to be demonstrated at the moment.  It does not seem unreasonable that 
multiple species of derived titanosaur could have been roaming around southern 
Mongolia at the same time.