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Re: Stegosaur volume of Swiss Journal of Geosciences

 >> This is to some degree a circular argument, because one of the
> reasons _Hesperosaurus mjosi_ was referred to _Stegosaurus_ by
> Maidment et al. (2008) was the overall similarity in plate size.
> This is despite the fact that the dorsal plates of _H. mjosi_ are
> of a different shape to those of _S. armatus_ and _S. stenops_,
> being "longer anteroposteriorly than tall dorsoventrally".

 So you agree Hesperosaurus has a different plate shape than
 Stegosaurus armatus or S. stenops then, leaving Stegosaurus' plate
 shape as distinctive. Thus armatus can be referred to Stegosaurus
 and doesn't cause any difficulties for phylogenetic nomenclature if
 it remains the type species.

The problem, as I see it, is that the ICZN sees it the other way around. *S. armatus* cannot be _referred_ to *Stegosaurus*, it _is_ *Stegosaurus* _by definition_. The question is whether *S. _stenops_* can be referred to *S.*.

...and if so, on what criteria. After all, the ICZN does not require genera to be monophyletic; it requires diagnoses, but those diagnoses don't need to contain any apomorphies.

Is it impossible to reliably distinguish *S. armatus* from at least two other named species that can be distinguished from each other? Then it's a nomen dubium, and AFAIK *S.* as a whole is a nomen dubium, too, and so is Stegosauridae. I'll look this up in the ICZN sometime.