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Re: Triassic Sauropods
<It is my understanding that a true sauropod--not a
melanorosaurid prosauropod--has now been found in northern
Thailand; I think the dinosaur is called Isanosaurus.>
*Isanosaurus* is from Madagascar, and the Isano series of
Triassojurassic strata, whereas the sauropod material from
Thailand is more typically Cretaceous (titanosaurs) and includes
prominently *Phuwiangosaurus.* More taxa from both Isano and
Thai strata are in prep. Work continues. Material recently
recovered from China (okay, 1991 is not _that_ recent...)
appears to indicate a fairly basal sauropod (my interpretation
of *Yimenosaurus*) and also Barrett and Upchurch's
interpretation of the jaws of *Yunnanosaurus*, which may not
pertain to that taxon anyway, based on its postcrania....
<shrug> Lack of concensus on where exactly melanorosaurids and
anchisaurid and *Thecodontosaurus* fit relative to sauropods and
*Ohmdenosaurus* and *Vulcanodon* [= "Vulcanodontidae"]. Better
interpretation of cranial material for these basal sauropods
will allow distinguishing primary morphoseries in Neosauropoda
and critique Wilson and Sereno (1999) and Upchurch (1995, 1998).
On *Isanosaurus*, this taxon is known from a postcranial
skeleton primarily distinguished by some proportions and the
prescence of a fourth trochanter that has a sigmoid
cross-section along its base (proximodistally on the femoral
axis). A larger, apparently sauropodan (large camerae in the
vertebrae, strait femur, etc.) that are distinguishable from the
"melanorosaurid" morphology. So, a postcrania that marks a
transition from the plateosaur to the vulcanodont morphology.
Does not elucidate what what not already known, but clarifies
hypotheses on transistory sauropodomorph morphology. The paper
was published mid last year in Nature, so the website will offer
the cite I don't have available right now....
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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