RE: Stegosaur volume of Swiss Journal of Geosciences

[Tim Williams <tijawi@yahoo.com>]

Michael Mortimer <mickey_mortimer111@msn.com> 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
> 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_.


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.


Cheers

Tim