RE: The New Paper at the End of the Universe (Was: Hitchhiker's New Papers to the Galaxy)

[Tim Williams <twilliams_alpha@hotmail.com>]

Jaime Headden wrote:

>   My rule of thumb is that if it's a tooth, don't name it.

I suspect a lot of fossil shark experts would disagree with you on that.  
:-)

> If it's been named,
> don't refer anything to it. If you have to refer something to it, it had 
> better
> be a tooth or contain a tooth in a jaw bone.

Yes - most dinosaur taxa based on teeth are indeed nomina dubia: _Deinodon_, 
_Aublysodon_, _Trachodon_, _Iguanodon_ (before a neotype was erected), etc.  
_Troodon_ is an exception - at the moment.  Still, I suspect _Troodon_ will 
be in trouble at some time in the future, given that the holotype is an 
isolated tooth.  _Astrodon_ is different in this respect (see below).

> The referal of bones, after naming at least, is
> generally justified on the grounds of comparability,

I guess my point was that if all the sauropod bones from a locality are 
compatible with the presence of one species (and ONE species ONLY), then 
does the holotype necessarily need to be diagnostic?  As long as the 
combined material (hypodigm) includes at least one diagnostic element, does 
it matter that the actual name-bearing element is not diagnostic?

With the Arundel situation, neither the respective type material for either 
_Astrodon_ or _Pleurocoelus_ appears to be diagnostic at the species level.  
So what do we do?  Do we declare both _Astrodon_ or _Pleurocoelus_ to be 
nomina dubia, and erect a new name that is attached to an element that is 
diagnostic?  This would seem to cause needless confusion.  Furthermore, 
making another element the holotype of this new genus is no guarantee of 
stability, because it is possible that this element may one day be found to 
be non-diagnostic too (i.e. if an element with identical morphology is found 
in a taxon outside the _Astrodon_/_Pleurocoelus_ type locality).

At the heart of this issue is this: If we have a taxon that is based on 
unassociated material from a single locality and horizon, do we need to shop 
around for a diagnostic element in order for the taxon to be valid?  I would 
say no.  As long as the combined material is diagnostic, who cares which 
element the name is attached to?

> and I am to understand the
> distinguishing of a bonebed as a type series must be done at the time the 
> type
> is designated (be it holo, syn, or lecto).

I'm not sure this matters, in the context of deciding (a) whether all 
material is assignable to a single taxon; or (b) whether a name is valid or 
not.  I would say, however, that in the case of a *lectotype*, this is 
designated *after* the type material is designated - when the original 
author(s) of the name did not designate which particular element of a type 
series or syntype should carry the name.

>   So my argument (I think I made it in response to Tidwell and Carpenter's
> paper at the time) is that *Astrodon* is simply too incomplete and limited 
> in
> diagnostic quality to justify it as possibly being referred to or having 
> any
> non-dental remains referred to it from any other taxon or remains.

Yes, it is true that the type material for _Astrodon_ is not diagnostic at 
the genus or species level.  But the same is probably also true for 
_Pleurocoelus_.  My point is that, given that both the _Astrodon_ and 
_Pleurocoelus_ types appear to be from the same species, and all the Arundel 
sauropod material also seems to belong to this species (because the 
morphology of the various elements is consistent with the presence of only 
one sauropod species), then any diagnostic element among the latter 
qualifies as a potential topotype.  I don't think either the names 
_Astrodon_ or _Pleurocoelus_ should be thrown onto the nomen dubium 
scrapheap when their types are contained within a hypodigm that is 
diagnosable at the genus/species level.

Wow, that was more pedantic and ranty than I thought it would be.  Apologies 
for the long-windedness.

Cheers

Tim

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