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Re: Alamosaurus as biggest North American sauropod
I think in these situations the correct thing to do is designate a
neotype. If T. rex is non-diagnostic relative new new taxa A and B, as
long as both are from roughly the same stratigraphic horizon and
geographic location, then pick one--it doesn't really matter which.
This is what the ICZN recommends be done for all nomina dubia and I
can't think of any better alternatives. However, I have seldom ever
seen this applied, except in the case of Coelophysis bauri. It's often
mis-applied, as in the case of Iguanodon, where rather than assign a
neotype for the species I. anglicus, a new type species was chosen,
probably unrelated to the original, and from a different geographic
location and stratigraphic horizon.
In related cases like Titanosaurus, the new, better specimens from the
same horizon, if they could not be differentiated from T. indicus,
should have been made the neotype of that species, rather than become
the basis of a new taxon which is almost certainly but unprovably its
synonym. If, later, this is contradicted by evidence that the original
material WAS distinct, or not really referable to the neotype, well
then so be it (IIRC this happened with Ceoplophysis as well). As least
the name is no longer attached to crap material cluttering up
Certainly, as in the case of _Alamosaurus_, it would be even worse to
suggest that new *less* complete remains from the same horizon as a
taxon from which they can't be differentiated represent a new taxon.
They can and probably should be considered Alamosaurus until there is
reasonable doubt over that assignment (from say, a second definitive
sauropod taxon found in the same horizon, evidence that smaller
Alamosaurus specimens are skeletally mature, etc.).
On Sat, Dec 10, 2011 at 1:48 AM, Mickey Mortimer
> Since my name was invoked as an acronym, I'll argue for the philosophy (not
> that it's uniquely mine). First I'll specify that a specimen must not differ
> from at least two other taxa in anatomical details which are taxonomically
> significant for it to be a nomen dubium. Note that the "taxonomically
> significant" clause leaves lots of room for subjectivity when it comes to
> Mesozoic dinosaurs. For example, the London and Munich Archaeopteryx
> specimens DO differ from each other, but I don't feel the differences
> indicate multiple taxa. If someone argues differently, I can point to
> examples of variation in other species (e.g. living ones, ones preserved in
> mass bonebeds), but ultimately it's a probability argument. Also note that
> stratigraphy, geography, ontogeny and sexual dimorphism can and should inform
> taxonomic evaluations, though I don't think differences in these areas should
> count as taxonomically significant (indeed the latter two are by definition
> NOT taxonomically significant).
> Given those caveats, I agree the philosophy isn't necessarily stable and will
> require revisions as more material is found. Maybe two or more taxa are
> hiding in what we now call Tyrannosaurus rex, and in that case if the
> holotype cannot be assigned to either species, it should indeed be declared a
> nomen dubium OR a neotype should be chosen among more diagnostic specimens.
> This is simply the price of science never presenting us complete knowledge.
> I'd like to know what your alternative philosophy is. Keep what are
> apparently two species synonymous, and thus not represent phylogeny with
> taxonomy? Pretend that the T. rex holotype can be referred to one of the
> species, and thus lie for the sake of stability?
> Mickey Mortimer
>> Date: Fri, 9 Dec 2011 08:10:27 -0500
>> From: email@example.com
>> To: firstname.lastname@example.org
>> CC: email@example.com; firstname.lastname@example.org
>> Subject: Re: Alamosaurus as biggest North American sauropod
>> On Thu, Dec 8, 2011 at 7:58 PM, Jaime Headden <email@example.com> wrote:
>> > The best strategy, in my opinion, is to simply do away with crap taxa.
>> > If you base your nomen on crap, and you can't distinguish it from two or
>> > more taxa (MMM = Mickey Mortimer's metric), regardless of its provenance,
>> > horizon, or the authors' preclusions about its ontogeny or gender, then
>> > that nomen deserves to be relegated to the annals of me laughing at you
>> > (the nomen, not the descriptors).
>> This is completely unsustainable and revisionist. _Titanosaurus
>> indicus_ was not a "crap taxon" when it was described. It was
>> perfectly diagnosable relative to knowledge of sauropods *at that
>> time*. A century of further discoveries rendered it "crap" *in
>> comparison to* more and better finds.
>> By this philosophy, we should never name any fossil taxa (or many
>> modern taxa for that matter) for fear that further research may render
>> previously diagnostic characters uninformative. Think the holotype of
>> _Tyrannosaurus_ is diagnostic? What if in ten years we find that, say,
>> the number of metacarpals varies between species of tyrannosaurines?
>> Or we find mummified specimens showing that some had different
>> patterns of squamation that could not be predicted by osteology? Even
>> if none of those specimens and no variation can be found within the
>> same geographic or stratigraphic level as the holotype, is the
>> _Tyrannosaurus_ then a declared a "crap taxon"?