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

The same observations that you are discussing here for
Nemegto and Opistho are occurring in Argentina for the
articulated skeleton of Epachthosaurus sciuttoi (see
JVP), devoid of neck'n skull, and the isolated neck'n
skull reported by Martinez from the same Bajo Barreal
Formation (was in the media some years ago, now under
study). As an interesting clue, they both are
plesiomorphical titanosaurs. Are they the same stuff?
How to know it? Because of the same formation? because
they are ONLY at 20 or 50 km? I think is not a very
useful discussion until we have at least one bone in
common (and in that case we will always fear that we
have no idea about the amount of variation that the
species could reach, or the ontogenetical states, we
only have a small fragment of a semaphoront). We have
no way to know the actual diversity of the Nemegt
fauna, only the fossilizable guys. 
Ok, ok, this is a gray morning in the Argentina
winter...but let's dream and someday we'll find a
complete Opistho and a complete Epachtho. Cheers.

 --- John Hunt <john.bass@ntlworld.com> escribió:

> I must admit to being puzzled by the phenomena
> alluded to by these posts.
> The probability of remains becoming fossilised is
> very small, so the chances
> of preservation of different parts of an animal that
> have been removed a few
> km apart must be tiny.
> John Hunt
> -----Original Message-----
> From: owner-dinosaur@usc.edu
> [mailto:owner-dinosaur@usc.edu] On Behalf Of
> Jaime A. Headden
> Sent: 26 August 2005 19:08
> To: dinosaur@usc.edu
> Cc: twilliams_alpha@hotmail.com
> Subject: 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).
>   Cheers,
> Jaime A. Headden
> "Innocent, unbiased observation is a myth." --- P.B.
> Medawar (1969)
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Lic. Sebastian Apesteguia
Seccion Paleontologia de Vertebrados
Museo Argentino de Ciencias Naturales 'B. Rivadavia'
Buenos Aires, ARGENTINA


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