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RE: Stegosaur volume of Swiss Journal of Geosciences
Tim Williams wrote-
> > 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.
But not if armatus is definitely within what we want to call Stegosauridae.
Sure armatus may be sister to stenops, or sister to latidens, because it could
be synonymous with either. But as long as it's definitely closer to stenops
than to Huayangosaurus, it's _just as good_ of an internal specifier as stenops
> > 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
> [don't you love how the DML snips off parts of your posts?]
I don't see how common sense tells us that, and indeed I think your opinion is
the one based on the ICZN's archaic rules. In phylogenetic taxonomy with no
Linnaean ranks, a genus is just another clade. So what's the big deal if the
type of your clade is not diagnosable within that clade, as long as it's
definitely a member? It's not like we're following the ICZN ideology of the
type of Stegosaurus being the model species.
> > 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
> > diagnosability.
> 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_.
I haven't actually read his paper or Maidment's contribution to the volume, so
I don't have an informed opinion. I think the lumping of Wuerhosaurus and
Hesperosaurus is purely subjective assuming all other species referred to
Stegosaurus (longispinus, laticeps, etc.) are more closely related to the
Stegosaurus type than they are to Wuerhosaurus and Hesperosaurus.
I will say Carpenter's abstract defending Hesperosaurus sounds completely
unscientific and thus pointless- "However, the validity of this genus has been
raising the question: how much osteological difference
among stegosaur taxa is needed to separate genera from
species? The question is examined vis-à-vis species and genus
in other dinosaurs, including iguanodonts, lambeosaurine
iguanodontids, chasmosaurine ceratopsians, tyrannosaurid theropods,
and diplodocid sauropods. The basis for taxonomic
distinction is largely philosophical: if the species are morphologically
distinct enough, they should be treated as separate genera.
Based on these criteria, Hesperosaurus mjosi is a distinct taxon."
I mean, really? First it's acting like there's anything to know by comparing
the situation in other dinosaurs, despite there being no reality to genera.
Then it recognizes the issue is subjective ("philosophical"), but somehow
Hesperosaurus meets the subjective criteria despite the fact Maidment obviously
felt otherwise. Your subjective opinions are wrong, Susannah! ;) Being the
first author of Hesperosaurus, I would think Carpenter's opinion on the matter
is both obvious and biased. And since the matter is completely opinion-based,
why have an article about it at all?
> 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.
The W. ordosensis material is lost, but you have a good point about the dorsal
number. The problem is that Dong (1993, not 1983 btw) did not use the dorsal
number as a species-level apomorphy, since the dorsal number is unknown in W.
homheni. So Maidment probably skipped over it accidentally, or else felt the
inability to locate the material justified making the taxon invalid. I don't
think either line of reasoning justifies making it a nomen dubium though.