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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.

Mickey Mortimer