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RE: What're Rebbachisaurids? (was - New Nemegtosaurus paper)

Tim Williams (twilliams_alpha@hotmail.com) wrote:

<Given that _Opisthocoelicaudia_ (once considered a camarasaurid) and
_Nemegtosaurus_ (once considered a diplodocoid) have both been moved into the
Titanosauria, based on very convincing evidence; and that the skull of
_Nemegtosaurus_ and the postcervical skeleton of _Opisthocoelicaudia_ were
found a few kilometers apart at the same stratigraphic level... this narrows
the odds that the two may be the same.  However, Wilson's point (and he is
absolutely correct) is that proof is needed - such as a specimen that includes
both cranial and postcranial material.  I'm sure Dr Currie feels the same way.
While it is tempting to synonymize the two, we cannot discount the possibility
that more than one titanosaur existed at this locality.>

  And to be honest, they were found at separate localities within the Nemegt
Valley, both corresponding to the same layer (Altan Ula [Or Uul] IV and Nemegt
Uul [or the classical Nemegtu locality] respectively above). That both were
included in one analysis (Currie-Rogers and Forster, 2001) and did not find
themselves as sister groups, prompting the use of Opisthocoelicaudinae as a sub
group of Saltasauridae implies one phylogenetic answer; but the presence of
several sympatric species of highly similar sauropod from the Morrison levels
indicates it _could_ happen elsewhere, and the caution of waiting for a better
specimen with head and body (would be nice if a neck, virtually nonexistent in
*Opisthocoelicaudia*, were also found).


Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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