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Re: Diagnostic Material

On 15 April 2010 18:07, Raptorial Talon <raptorialtalon@gmail.com> wrote:
>> It certainly can't be done by number of bones - just saying "a specimen 
>> composed of one vertebra/whatever can't be diagnostic" doesn't work, because 
>> of stuff like <i>Xenoposeidon</i> - one partial vertebra, tons of 
>> distinctive characters.
>  . . . which falls apart if several new taxa are found to have those
> features. And the cycle continues.

Typically of course it doesn't fall apart at all.  If a given new
taxon is distinguishable from Xeno, then it's a new taxon; if it's not
distinguishable, then it's a specimen of Xeno.  The only was Xeno can
become "non-diagnostic" would be if multiple new specimens were found
which both had all the Xeno characters but which also were
distinguishable from one another.  In that case, Xeno's diagnosis
becomes diagnostic at a higher level, that of the clade containing the
new taxa and Xeno Classic.  (This is what happened to Titanosaurus.)
Whether you would then feel the need to take Xeno down would depend on
whether you felt genera and clades were different things and whether
you felt that all genera had to be monophyletic.

> Not that that's likely or anything in this case - that's just how
> those gray areas develop.