Re: Hanson 2006, Mortimer, Baeker response

[Michael Mortimer <mickey_mortimer111@msn.com>]

Tim Williams wrote-

> _Tendaguria_ could be a highly aberrant basal titanosaurian - if (and I 
> mean IF) it is the same as _Janenschia_.  Bonaparte et al. (2000) split the 
> _Janenschia_ material three ways: limb bones (retained in _Janenschia_); 
> presacral vertebrae (assigned to a new sauropod, named _Tendaguria_); and 
> caudal vertebrae (unnamed).  But the limb bones and presacral vertebrae 
> both come from a VERY heavily built sauropod; the caudals are strongly 
> procoelous; and the limb bones also show titanosaur characters.  The 
> dorsals of _Tendaguria_ are just plain weird (puny neural spines, massive 
> transverse processes), and this makes _Tendaguria_ hard to place.  If 
> _Janenschia_ and _Tendaguria_ prove to be the same after all, then this 
> sauropod is a titanosaur with highly autapomorphic dorsals.

Tendaguria seems to have gotten its own family largely because Bonaparte was 
being more phyletic than cladistic.  The dorsals were different enough from 
Saltasaurus that he figured it deserved to be separated.  But he said the 
same thing about Malawisaurus.  The general morphology of the dorsals looks 
more similar to titanosaurs than other sauropods, and I wouldn't be 
surprised to see it as a titanosaur in a cladistic analysis.

> As for _Agustinia_, the problem here is that this sauropod is too poorly 
> known to confidently ascertain its relationships.  The presence of body 
> armor suggest titanosaur affinities, but I admit this doesn't seal the 
> deal.

New material has been found (used in Curry Rogers' thesis' analysis) and 
shows it was a titanosaur.

In regard to the theme of this thread, finding 'new' categories of dinosaurs 
is impossible in a way.  At least in the sense of broad groups like 
Sauropoda.  After all, Dinosauria is defined to only include Saurischia and 
Ornithischia.  So any dinosaur has to fall into those clades.  Saurischia is 
defined to only include Sauropodomorpha and Theropoda, so again, any 
saurischian will be one of those.  A sauropodomorph is either going to be a 
prosauropod, a sauropod, or more basal (like Saturnalia, Thecodontosaurus, 
etc.).  And similar statements could be made for any dinosaur group.  Our 
current knowledge and phylogenetic taxonomy give us a well-supported 
backbone, and all that's left is to fill in the gaps.  But that's how it is 
with any clade of organisms whose phylogeny is well known.  And the gaps are 
sometimes huge.  So there's still plenty of work to do.

Mickey Mortimer