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

Mike Taylor wrote:

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.

Probably most sauropods do have autapomorphies - but by no means all (including some of those that are traditionally considered 'valid'). Like Mickey, I think the requirement that each genus/species have at least one autapomorphy in order to be deemed 'valid' is setting the bar way too high. IMHO, having a unique *combination* of characters should be enough for a diagnosis. I'm certain _Apatosaurus_ has this. For _Titanosaurus_, I think this is a little trickier.

OK Mike, take a deep breath - I'm going to use a non-sauropod example. I've heard that autapomorphies are hard to find in _Archaeopteryx_. But, _Archaeopteryx_ is valid, right? It can be distinguished from every other theropod taxon, just as _Apatosaurus_ can be distinguished from any other sauropod taxon. Therefore, the validity of these genera is beyond reproach.

Rauhut (2004) upheld the validity of _Genyodectes_ based solely on a unique combination of characters. It had not a single autapomorphy.

Mickey Mortimer wrote:

> 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.

Yes, it's called "plausible deniability". Everyone knows the truth, but no one can prove it. :-)

I was really trying to illustrate the difficulties of *proving* that a higher-level taxon is derived from a genus name.