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Re: Rabdomorpha question



Mark Van Tomme (markvantomme@yahoo.com) wrote:

<Is the clade Rabdomorpha valid? It was coined by Pincemaille in her doctoral
thesis in 1997 but never published by the author, I think.. Pereda-Superbiola
and Sanz 1999:266 briefly mentioned it but only gave a few characters of the
group.>

  While both Ruiz-Omeñaca and Pereda-Suberbiola & Sanz have mentioned the name,
neither have attached it to a particular monophyletic group of ornithopods, the
grouping usually used are *Rhabdodon*-like and thus tending to be
plesiomorphic, and the name has never beed defined to have a particular
meaning. So, no, it's not "valid" yet. I asked Pincemaille sometime ago about
this name, and she doesn't seem to be in a hurry to publish it, but she is
working on the higher ornithopods and will possibly further conclude the fate
of this informal name. So far, if you're a large-headed, boxy-skulled,
semi-quadrupedal non-iguanodontoid, non-hadrosauroid, non-"hypsilophodontian"
ornithopod, then you are a "rhabdomorph", and this is a very tricky area in
that in the last several analyses released to include several of these taxa,
including *Tenontosaurus*, *Gasparinisaura*, *Rhabdodon*, *Zalmoxes*, and
*Anabisetia*, the relationships and even internal monophyly of these taa has
been questioned; indeed, some "hypsilophodontians" like *Parksosaurus* and
*Leaellynasaura*, *Qantassaurus* and *Atlascopcosaurus* as well as
*Muttaburrasaurus* appear to be included in this group based on jaw features
and in some cases postcrania, and *Tenontosaurus* and *Rhabdodon* may very well
be paraphyletic (representing different "grades" of animal rather than a
monophyletic group).

  Pete Buchholz has done some work regarding this complex, but this is as yet
unpublished for the most part, and some of the comments come from work he has
produced.

  It also doesn't help that "Hypsilophodontia" appears to be a paraphyletic
grade of three or more groups of ornithopods, and some "hypsilophodontians"
appear to be non-ornithopods, perhaps thyreophorans or more basal;
*Heterodontosaurus* appears to be allied to Marginocephalia, but not as a
member of it (the current -- and only? -- definition excludes it).

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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