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Re: Sauropods



Dino Rampage wrote-

> 1) I understand that Antarctosaurus wichmannianus is now considered a
> diplodocoid (Is it?) How about the other two species of 'Antarctosaurus',
> "A". giganteus and "A". brasiliensis? The skull illustration on  DINODATA
> shows a skull that could be diplodocoid, but yet at the same time, it
could
> also be titanosaurian. Is this the most recent reconstuction of the skull?
> And if A. wichmannianus is indeed diplodocoid, does it show affinities to
> dicraeosaurids, rebbachisaurids or diplodocids?

Antarctosaurus may be titanosaurid (Curry Rogers and Forster, 2001) or
rebbachisaurid (Sereno and Wilson, 2001).  Then there are suggestions the
braincase is titanosaurid and the mandible rebbachisaurid.  Upchurch (1999)
supported the chimaerical nature by noting the mandible was wider than the
occiput, but the odd jaws of Nigersaurus were not known at the time.  He
supported a nemegtosaurid position, though these are now thought to be
titanosaurs.  The fragmentary postcrania are titanosauroid (biconvex
proximal caudal; radiometacarpal ratio pver .45; dorsoventrally elongate
lateral muscle scar on fibula), but just to add confusion, some or all may
not belong with the skull.  I've heard A? giganteus is titanosaurian,
perhaps based on the proximolateral femoral bulge.  A? brasiliensis is a
probably indeterminate titanosaurid based on the eye-shaped dorsal
pleurocoels (Kellner and de Azevedo, 1999).  The most recent skull
reconstruction is by Salgado and Calvo (1997) which shows a more macronarian
structure than Huene's (which the Dinodata one is based on).

> 2) The DINODATA site also has a skull illustration of Alamosaurus
> sanjuanensis. However, it looks extremely diplodocid to me. Most
> reconstructions I have seen of Alamosaurus have given it a Camarasaur-like
> head. Since when have cranial elements been found? And are there any good
> restorations or skeletal reconstructions available on the Internet? And is
> it closely related to Saltasaurus? Would it be okay to give it dermal
> armour?

There are no cranial remains known for Alamosaurus, the picture on Dinodata
must be a faked cast.  A good skeletal reconstruction was recently included
in Lehman and Coulson (2002).  It seems closest to Titanosaurus and
Opisthocoelicaudia, though titanosaur phylogeny is highly unstable.  Dermal
armor has a sporadic distribution in titanosauroids, possibly caused by
preservation problems.  No titanosaur armor has been found in North America,
so it was possibly unarmored.

> 3) I have heard recently that Seismosaurus hallorum is most likely a large
> specimen of Diplodocus. How about Supersaurus vivianae? Is it still a
> separate taxon or is it more likely to be a large Diplodocus/ Barosaurus?
If
> these two are indeed large individuals of Diplodocus, would it be more
> likely that they be assigned their own species (eg. Diplodocus hallorum,
D.
> vivianae) or would they be sunk into the existing species of Diplodocus?

The placement of Seismosaurus hallorum in Diplodocus (as D. hallorum) is so
far based on unpublished evidence (Curtice, pers. comm. to Lucas 2000).  It
will probably end up being a subjective decision to synonymize it, as it's
certainly a distinct taxon.  Supersaurus was a valid diplodocid last time I
checked.  I don't think D. vivianae has even been published.

> 6) I've been hearing about the apparently unique dentition of Nigersaurus,
> as well as the supposed sail on Rebbachisaurus garasbae. Any good
> restorations to refer to and give me some idea of how they may have looked
> like in the flesh?

Sereno showed a slide at SVP 2001 with a lateral view of Nigersaurus' skull.
I can't recall seeing the single known dorsal vertebrae of Rebbachisaurus
garasbae in any publication.

> 7) Does Argentinosaurus show any affinites with the other two giants,
> Paralititan and Bruthakayosaurus? All three are gigantic titanosaurs, and
> all three are found in different regions of Gondwana. Any evidence to
place
> this trio into their own family of giant titanosaurs?

Titanosaurian phylogeny is not stable now, and neither Argentinosaurus nor
Paralititan have precise placements in the cladogram.  Paralititan may be
more derived than Andesaurus and Argentinosaurus may be somewhere near
Andesaurus.  Bruhathkayosaurus is too poorly illustrated and described to
code for an analysis, assuming Chatterjee's correct in calling it a
titanosaurid.

> 8) I've seen many place Rapetosaurus close to Nemegtosaurus. Has any
dermal
> armour been discovered in association with Rapetosaurus? If so, can we
draw
> Nemegtosaurus with armour? Or is Nemegtosaurus more likely to be in fact a
> diplodocoid, as some members of the list think so? (Personally, I find it
> hard to believe that the diplodocids, dicraeosaurs, rebbachisaurids,
> brachiosaurs, camarasaurs and a whole host of other sauropod groups could
> have survived with the titanosaurs)

Titanosaur osteoderms have been found in the Maevarano Formation, but I
don't think any have been associated with Rapetosaurus yet (there is another
titanosaurid there too).  The discovery of Rapetosaurus has pretty much
guaranteed the placement of nemegtosaurs in the Titanosauria.  Draw
Nemegtosaurus with armor or without, we have no postcrania.  As for the
suggestions titanosaurs are polyphyletic and currently include some
camarasaurids, diplodocids, etc., I find this unlikely.  Since the
mid-nineties, the use of cladistic methodologies has moved several
previously non-titanosaurian taxa into the clade (Opisthocoelicaudia,
Nemegtosaurus, Chubutisaurus), the opposite of what would be expected if
various families were just converging with titanosaurs.  I still don't like
the idea that Euhelopus is a titanosaur though.

Mickey Mortimer