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RE: Ceratops (was RE: Pterosaur diversity (was: Re: Waimanu))

Mike Taylor wrote-

1. I think everyone agrees that, based on the type material,
   _Titanosaurus indicus_ is not diagnosable from other titanosaurs,
   so that species, which it was once valid, is now a nomen dubium.  I
   think it's important that this change has happened not because of a
   change in attitude to the original material, but a change in the
   context in which it's evaluated, i.e. we now have dozens of
   sauropods with procoelous caudals, so that this character is no
   longer diagnostic.

No, I don't think that's been demonstrated. What Wilson and Upchurch (2003) did was take the characters originally used to diagnose Titanosaurus indicus (back in 1877) and show that each one isn't unique among sauropods. Not really surprising. As a comparison, Upchurch et al. (2004) found that none of the original apomorphies of Apatosaurus (also from 1877) are valid anymore. And of the eleven apomorphies they consider valid for Apatosaurus, four are seen in other sauropods, while five can only be observed in one specimen of Apatosaurus and involve bones not commonly found in sauropods (braincase, atlus, astragalus). And this is Apatosaurus! An extremely distinctive genus known from multiple fairly complete specimens. Using Wilson and Upchurch's criteria, very few sauropod genera would be valid.
Of course, we now know titanosaur vertebrae can exhibit a lot of variation within the caudal series. But this doesn't mean they were completely variable, and that any morphology could be found in one taxon, making them taxonomically useless. An analogy is theropod teeth. While they do exhibit positional variation, it's still possible to identify a tooth as Tyrannosaurus, Ceratosaurus, Masiakasaurus, etc.. So until someone shows me two taxa with caudals identical to Titanosaurus, I won't be convinced it's a nomen nudum.

3. If we consider names ending -idae (etc.) to be "family-level" and
   therefore governed by the ICZN, then Wilson and Upchurch (2003) are
   right that Titanosauridae must also die;

Er, why? The ICZN only recommends (not requires, I think) poorly known taxa not be used. It says nothing about indeterminate taxa.

> This could be harder to prove.  After all, unless an explicit
> etymology is provided for each clade, it is open to interpretation
> whether it is named *after* a given genus.  For example, we know
> that when Titanosauria was first named (was it by Bonaparte and
> Coria, 1993?) it was ultimately named after _Titanosaurus_; but
> unless this is explicitly stated in the paper, the name could just
> be a descriptive term in its own right ("titan lizards").

That's really stretching plausibility there.

Mickey Mortimer