What, if anything, is _Apatosaurus_ (Was: Ceratops (was RE: Pterosaur diversity (was: Re: Waimanu)))

[mike@miketaylor.org.uk (Mike Taylor)]

Michael Mortimer writes:
 > 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.

I admit this kind of talk worries me.  We all know what _Apatosaurus_
is.  A while back, someone on this list came up with the idea of "the
pornographic definition of birds" which is "I know one when I see
one".  That's sort of how I feel about _Apatosaurus_.  The moment you
see one of those honking great cervical ribs, you know what you're
dealing with instantly.  So how can it be that in a cladistic
analysis, such an obviously distinctive character counts for no more
than, say, an unobtrustive rugosity on the lateral face of the distal
part of pedal phalange II-2?  That's just wrong.

 > Using Wilson and Upchurch's criteria, very few sauropod genera
 > would be valid.

Really?  What are the criteria that you allude to exactly?  That each
valid genus should be diagnosed by at least one autapomorphy?  I would
think that most sauropod genera have that.

 >> 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?

Because (early in the argument) I posited that _Titanosaurus_ is
rightly considered a domen dubium.  If you contest that assumption,
the rest of the argument doesn't follow.

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