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RE: Stegosaur volume of Swiss Journal of Geosciences
Michael Mortimer <firstname.lastname@example.org> wrote:
> I disagree. "Diagnostic" and "well known" are not
> synonyms. Titanosaurus is very well known regardless of
> its diagnosability, for instance. I bet more people know
> about it than know about Isisaurus, Baurutitan, or most
> other sauropods for that matter.
I interpreted "well known" to mean "well known scientifically", rather than
"famous". But as you say, the ICZN is unhelpful as to what it exactly means by
"well known"; and it's only a recommendation anyway. Bring on PhyloCode!
> Indeed, as we discussed before,
> a nomen dubium can be an OTU in an analysis, it will just
> have more than one equally parsimonious position (assuming
> the taxa it's indistinguishable from were also included).
But if a taxon/OTU has more than one equally parsimonious position in a
phylogeny, it can't be such a great choice for defining a clade. Let's look at
_S. armatus_, a nomen dubium according to Galton. If we use _S. armatus_ to
define Stegosauridae, and _S. armatus_ comes out in multiple positions in the
same phylogeny... then a given taxon can be both inside and outside
Stegosauridae at the same time.
> I don't think it's necessary. With Iguanodon, the
> referred species did not necessarily form a clade with I.
> anglicus, which was in turn difficult to analyze due to its
> incompleteness. So knowing if other species were really
> Iguanodon was difficult as was knowing which taxa were
> iguanodontids. But with Stegosaurus, S. armatus is deeply
> nested in Stegosauridae and forms a clade with referred
> Stegosaurus species. Since there's no rule about type
> species having to be diagnostic within their genera, I don't
> think the issue merits an ICZN ruling.
Hang the ICZN and its archaic rules! Commonsense tells us that it's
problematic to have a genus for which the type species is non-diagnostic.
That's why a new type species was designated for _Iguanodon_: _anglicus_ was
abandoned in favor of _bernissartensis_. So obviously the ICZN saw the
> It's better than sinking Stegosaurus in favor of
> "Eustegosaurus stenops" or something at least.
Well, the solution offered by Galton and Carpenter is to retain _Stegosaurus_
with a new (diagnosable) type species (_stenops_). It's the best way around
the issue of a non-diagnostic type species (_armatus_).
> Note too that Galton's opinion on Stegosaurus taxonomy
> isn't representative of all stegosaur experts, as Maidment
> (2008) found S. armatus to be a senior synonym of Diracodon
> laticeps, Hypsirophus discursus, Stegosaurus stenops and S.
> duplex, while S. longispinus and S. sulcatus were nomina
> dubia. Which is a fairly good argument in itself not to
> base taxonomic rules on subjective concepts like
In the Swiss stegosaur volume, Carpenter disputes most of Maidment's 'lumping'.
As he rightly puts it, some characters stated by Maidment et al. (2008) to be
variable in _S. armatus_ (and therefore used to synoymize other stegosaur
species under _S. armatus_) are used in the same study to diagnose other taxa
(such as _Gigantspinosaurus_). I was never comfortable with having
_Hesperosaurus_ and _Wuerhosaurus_ referred to _Stegosaurus_.
Speaking of _Wuerhosaurus_... there is no mention of the type material of _W.
ordosensis_ in the volume. This is the specimen that reportedly has only 11
dorsals, according to the original description (Dong, 1983). Maidment et al.
(2008) dismissed _W. ordosensis_ as a nomen dubium; but 11 dorsals constitutes
a very short trunk, and implies a very long neck if the extra dorsals were
cervicalized. Something to mention here while the stegosaurs are enjoying
their time in the spotlight.