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Some Comments Re: Antarctosaurus



George Olshevsky (Dinogeorge@aol.com) wrote:

<There's a small problem with classifying Antarctosaurus as a
rebbachisaurid. Antarctosauridae Olshevsky, 1978 has priority over
Rebbachisauridae, which was created much more recently (don't recall
citation/reference off top of head; Sereno? Wilson & Sereno?). And if one
classifies Antarctosaurus as a "titanosaurid," a family name based on a
nomen dubium, then one needs to choose the next available family name for
Titanosauridae, which would be, guess what--Antarctosauridae Olshevsky,
1978.>

  Indeed, Rebbachisauridae was named in 1996 by Bonaparte for a clade
comprising *Rayososaurus* and *Rebbachisaurus* (latter containing two
species, *garasbae,* *tessonei* [*Limaysaurus*], and one problematic
species *tamesnensis* which may be *Nigersaurus*).

  However, this all depends on what is picked as the lectotype, which has
not yet been done (and I think there are one or two guys in Argentina
looking at this right now, one of which may be Leonardo Salgado, but I'm
not very sure). The braincase is that of a nemegtosaurid and possibly
scapula as well, the caudals (and maybe the limbs) that of a
pellegrinisaurid or saltasaurid (which already may supplant
Titanosauridae), and the jaw as a rebbachisaurid. The difficulty here is
the majority of titanosaurs already in Argentina. It is possible that it
is synonymymous with one or another already known rebbachisaurid, or even
*Nigersaurus* (closer in space and time to *Nigersaurus* of the Aptian,
rather than *Rayososaurus* / *Limaysaurus* / *Rebbachisaurus* which are
Campanian--Maastrichtian in age.

  Then you would have to prove that Antarctosauridae is convergent on
Rebbachisauridae rather than a sister group. After selecting one of three
macronarian morphologies as a type, depending on what von Huene may have
implied in his collection of a type. A new saltasaur, *Rocasaurus
muniozi*, is also known from the same level as the type (General Roca, Río
Negro Pr., Allen Fm.), but there are no overlapping elements.

  Without being an expert on titanosaur mid-caudal veriation and
distribution of features, I would not discount *Titanosaurus indicus* just
yet. No one has proven the likelihood of synonymy with any other taxon,
and so far, it does possess unique features (Jain and Bandyopadhyay, 1997)
that permit some comparison to the majority of Titanosauriformes, and this
may still be enough to save the taxon, just not the referral of countless
species to it.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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