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Re: Alamosaurus as biggest North American sauropod

Importantly, the ICZN is about nomenclature and only nomenclature, not about classification. Therefore, about lots of very important questions, it says "I don't know, and I don't care". It -- guarantees what it calls "taxonomic freedom" to such a degree that it doesn't contain any rules about how to delimit taxa; -- insists that every organism that is to be classified at all must be referred to a species, but doesn't even pretend to define "species" at all, and doesn't even consider the fact that many species concepts (arguably all interesting ones) cannot be applied to most fossils*; -- hardly mentions the term "nomen dubium" and does not define it. It's mentioned in the glossary but only explained as "[a] Latin term meaning 'a name of unknown or doubtful application'."** All the rest is left to taxonomic freedom.
The whole thing is here: http://www.nhm.ac.uk/hosted-sites/iczn/code/ . Everyone should read a few parts of it, in particular the principles (click on "Introduction" in the left sidebar).
* Many species concepts require that you can at least approximate some kind of population biology. Even with a bonebed, you can't get very far in that direction. ** Obviously, the term itself doesn't even mean that. It's just "doubtful name". 


> 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,

 Um, maybe it's just my dialect of English, but as far as I know, "to
 either" refers to the aforementioned number - in this case, "two or
 more". So, either the holotype fits in one of the "two or more
 taxa"...or someone miscounted how many taxa there are to select
 from.
That's exactly what Mickey is trying to say: _assuming_ that everyone miscounted, which of the two or more species does the holotype belong to, so that that species (and not the other[s]) must be called *T. rex*? 


> 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?

 the holotype *has to* belong to a species.
In this hypothetical situation, and in many, many real situations, we cannot tell which of two or more species it belongs to -- and which of those species therefore must bear the species name that is attached to that holotype.