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RE: Stegosaur volume of Swiss Journal of Geosciences
Jay wrote and Tim Williams replied-
> > Okay, lets assume for now the material of S. armatus can be
> > distinguished from Huayangosaurus, thus allowing stegosaurs
> > to be placed in either Stegosauridae or not with S. armatus
> > and H. taibaii being internal and external specifiers
> > respectively:
> > What if the issue is that the S. armatus material cannot be
> > discriminated from that of Hesperosaurus, Dacentrurus,
> > Loricatosaurus, Miragaia, Tuojiangosaurus, Wuerhosaurus etc?
> > In this case, while the clade 'Stegosauridae' may continue
> > to be upheld under your proposal, the clades Stegosaurinae,
> > Dacentrurinae, and all the above genera would not if S.
> > armatus was an internal specifier. Would all these taxa then
> > be squeezed into 'Stegosaurus'?
> Jay hit the nail on the head here. There is no point of having a genus if the
> type species is invalid. As Jay points out, if _S. armatus_ is found to be
> not diagnosable at the genus level, but only at a higher taxonomic level
> (e.g, family or subfamily), then the entire concept of _Stegosaurus_ is
> destroyed. After all, a genus is only as good as its type species. The entire
> point of a type species is to literally typify the genus.
> This is why, when a type species is declared a nomen dubium, there are only
> two options: (1) retain the genus by designating of a new type species; (2)
> abandon the genus that is typified by the type species. For _S. armatus_,
> option (1) seems the most appropriate, as was done with _Iguanodon_ before it.
But I'm betting armatus CAN be distinguished from non-Stegosaurus stegosaurids,
since it preserves a large plate. Dacentrurus, Wuerhosaurus, etc. all have
smaller plates than Stegosaurus, with Wuerhosaurus' being very low,
Tuojiangosaurus' being narrow and triangular, etc.. Diagnosability is not an
all or nothing concept. A taxon can be diagnostic at "genus level", yet be
undiagnostic within that genus. In that case, it should be fine to have the
type species be a nomen dubium. If armatus does prove undiagnostic relative to
Stegosaurus' sister genera, then I'd agree we should make stenops the type
species. But nobody's claimed that's the case yet.