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



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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