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Re: Rapetosaurus stuff



I'm sorry if this comes through twice, but I don't think it made it the
first time.

Thomas Holtz wrote-

> According to their analysis, Alamosaurus is a basal member of a clade also
> containing the Indian Titanosaurus colberti, South American Neuquensaurus
> and Saltasaurus, and Asian Opisthocoelicaudia.  However, I would REALLY
> like to see this analysis rerun by combining the Opisthocoelicaudia and
> Nemegtosaurus data in the matrix, and seeing how it changes the results.

First off, the basal parts of the titanosaur section are really unstable.
While converting the matrix to a NEXUS file, I accidentally ran it ordered
(the authors ran it unordered) and found Titanosaurus, Alamosaurus, the
Opisthocoelocaudia-saltasaurine clade and the nemegtosaurid clade in a
polytomy.  Setting it to unordered gave the results in the paper.  Combining
Nemegtosaurus and Opisthocoelocaudia into a single OTU resulted in 82 MPT's
of 452 steps each.  A large polytomy of Euhelopus and titanosaurs was
present.  Comparing sample trees revealed the polytomy to be the result of
Antarctosaurus jumping into various positions.  Removing it resulted in only
6 MPT's of 449 steps.  These had the following topology within the
Titanosauria (otherwise identical to the original tree)-
________Euhelopus
|________Malawisaurus
   |_______Rapetosaurus
     |______Alamosaurus
        |_____Titanosaurus
        |_____Opisthocoelocaudia/Nemegtosaurus
           |____Quaesitosaurus
              |___Neuquensaurus
              |___Saltasaurus

I've read that there is no justification for assigning all North American
Late Cretaceous titanosaurids to Alamosaurus, as multiple genera could be
present.  This, and combining the braincase assigned to Titanosaurus indicus
with T. colberti's postcrania, may have influenced the results.

> Previous studies have suggested that the Thai dinosaur Phuwiangosaurus is
> a titanosaur, possibly close to the nemegtosaurs.

Indeed.  Tangvayosaurus from Laos and Huabeisaurus from China are also close
to Phuwiangosaurus.  Other basal titanosaurs are known from the United
States (Texan "Pleurocoelus") Europe (Macrurosaurus), Argentina
(Chubutisaurus) and Australia (Austrosaurus).

> On the other hand, if the Dinosaur Park
> Formation therizinosaur frontal described by Currie in the 1980s IS a
> therizinosaur, then those guys were hanging out in the Judith River Group
> without leaving a tooth record (as far as has been reported).

North American segnosaur records are really piling up.  Besides
"Nothronychus", we have the undescribed Early Cretaceous Utah form,
Gillette's new Late Cretaceous Utah form, the elements (frontals, pedal
ungual, other?) from the Dinosaur Park Formation, the Hell Creek astragalus
Tom reported on earlier and a cervical from the Scollard Formation.

Mickey Mortimer