Re: Notes on Rebbachisaurs and Tehuelchesaurus (less longish)

["Timothy Williams" <twilliams_alpha@hotmail.com>]

Dann Pigdon wrote:

> This is interesting, since the Australian Mid-Jurassic sauropod 
> Rhoetosaurus has
> been suggested as being euhelopodid. With Austrosaurus now considered by 
> some as
> a titanosauriform, perhaps the authors may have a vested interest in 
> finding
> another Gondwanan Mid to Late Jurassic euhelopodid?

It may depend on how you define/diagnose the Euhelopodidae.  Two different 
phylogenetic schemes (that of Wilson and Sereno and that of Upchurch) have 
put forward very different affinities for _Euhelopus_, even though they 
agreed in most other aspects of sauropod phylogeny:

Upchurch unites _Euhelopus_ with _Omeisaurus_ and _Mamenchisaurus_ as a 
clade of basal neosauropods (Euhelopodidae).  Wilson and Sereno regard 
_Euhelopus_ as a derived titanosauriform, as the sister taxon to the 
Titanosauria, and a long way from _Omeisaurus_.

_Rhoetosaurus_ has been linked to _Shunosaurus_ and _Omeisaurus_ (the 
shunosaurines of McIntosh).  _Rhoetosaurus_ reportedly does have forked 
("skid-like") chevrons, although Upchurch rejected Macintosh's placement of 
_Rhoetosaurus_ in the Shunosaurinae (euhelopodids in Upchurch's 
classification) and cast doubt on its possesion of forked chevrons.  At any 
rate, Wilson and Sereno claim that forked chevrons have a wider distribution 
among sauropods than just the shunosaurines and diplodocoids.  Apart from 
this character, I can't think of one character to link _Rhoetosaurus_ with 
the shunosaurines/euhelopodids. If I'm wrong, feel free to fire away!

> The classification of
> Austrosaurus and Rhoetosaurus would suddenly make sense,

_Austrosaurus_ seems fairly comfortable in the Titanosauriformes.  Based on 
characters in the femur and vertebrae it appears to be close to the 
Titanosauria.  I don't think the same can be said for _Rhoetosaurus_.


> Australia abelisaurs, any one?

Ralph Molnar once put _Rapator_ among the abelisaurs.  With only a single 
metacarpal to base his assessment on, I'm not at all sure why he did this.


Tim


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