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Re: New sauropod refs: Rinconsaurus & Amygdalodon

Jaime A. Headden wrote:

  And one of the main reasons why I argue the possibility of both caudal
convexity or concavity as well as many other potential and variable
features of vertebrae (such as neural spine bifurcation) in some sauropods
isn't as important as we assume, and cannot be used to account for (or
discount) the phylogenetic relationships of *Opisthocoelicaudia.* This is
in contest to the so-called support for *O.* being a camarasaur;

I couldn't agree more. (To provide some background, some ardent opponents of cladistics are convinced that _Opisthocoelicaudia_ is actually a camarasaur. Thus, according to this viewpoint, phylogenies that put this taxon in the Titanosauria reveal the flaws of cladistic methodology.)

Now the question arises: HOW did _Opisthocoelicaudia_ get its opisthocoelous tail? Did individual tail vertebrae change over to opisthocoely one-by-one from a procoelous and/or amphicoelous condition? Or did the entire tail (except for the terminal vertebrae) switch over to the opisthocoelous condition in one homeotic swoop? Either way, it's a fascinating transformation.

The other question: WHY did _Opisthocoelicaudia_ have an opisthocoelous tail? What was the selective advantage of this feature?

  Forgive me if I am mistaken, but were not teeth also known and the
source of the designation "almond tooth," and hence, wouldn't the type be
best considered to pertain to that tooth, and vertebrae if diagnostic
rendered to another, if unnamed, species? Kinda defeats the spirit of the
name and reference thereafter.

Then we have _Vulcanodon_, a sauropod for which the teeth are not yet known. (The teeth that were found with the type material belong to an indeterminate theropod, and the name _Vulcanodon_ was subsequently restricted to the skeletal material.)



Tim

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