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RE: Titanosaurian Nemegtosaurs, Batman! (Was: Caudipteryx and sauropod embryos)



Mike Taylor wrote:

And _Nemegtosaurus_ (along with _Quaesitosaurus_) still falls out as a
basal diplodocoid in the analysis of Upchurch, Barrett and Dodson 2004
in _The Dinosauria_, 2nd edition.  I spoke to Paul Upchurch at the
SVPCA last year, and he said that he does now accept titanosaurian
nemegtosaurids, but that he'd not managed to get a cladistic analysis
to show this position.  Go figure.  Mind you, the cladogram doesn't
show _Rapetosaurus_ as an OTU, so maybe when that's introduced into
the matrix it will change everything.

You could be right. Also, poor _Nemegtosaurus_ (like _Quaesitosaurus_) is known only from a skull - that may partly explain the instability of the nemegtosaurids. _Rapetosaurus_ (which has a well-preserved skull, bless him) would probably help. Now, if the skull of _Nemegtosaurus_ does belong to the postcranial skeleton named _Opisthocoelicaudia_, then things could get really interesting. (With the exception of a few amateur taxonomists, most researchers are convinced that _Opisthocoelicaudia_ is a true titanosaur, not a camarasaurid or euhelopodid.) In this event, _Nemegtosaurus_ would have priority over _Opisthocoelicaudia_ (1971 vs 1977), but Opisthocoelicaudiidae would have priority over Nemegtosauridae (1995 vs 1990).


Other oddities in the Upchurch et al. 2005 cladogram:
_Haplocanthosaurus_ comes out as a macronarian closer to titanosaurs
than _Camarasaurus_ is;

_Haplocanthosaurus_ just doesn't want to fit in. If _Morosaurus agilis_ is referrable to _Haplocanthosaurus_, it may help resolve its position.


and Euhelopodidae comes out as a paraphyletic
sequence of outgroups to Neosauropoda, similar to Wilson 2002, except
that here Euhelopus is non-neosauropodan rather than titanosauriform.

As well as other "euhelopodids", _Euhelopus_ also comes out close to _Lourinhasaurus_, according to this analysis.


I mistrust paraphyletic euhelopodids (even when they bear gifts)

If a mamenchisaur brought you a six-pack of Guiness, I'm sure you'd change your mind.


on
palaegeographical grounds.  Since Upchurch also does palaegeography
work, I am surprised he's not making more of a fuss about this.

Yes, Upchurch et al. (2005)'s cladogram fails to come up with a clade comprising _Omeisaurus_, _Mamenchisaurus_ and _Euhelopus_. I'm not so much bothered by the paleographical implications, but by the implication that the addition of extra cervicals evolved more than once in three closely related Asian genera.