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2011/1/18 David Marjanovic <firstname.lastname@example.org>:
>> And as I'm sure you know, Wilson and Upchurch 2003 showed that the
>> genus Titanosaurus is no longer diagnosable, and that according to
>> ICZN rules this means that co-ordinated family-level names such as
>> Titanosauridae should no longer be used.
> They showed the former, but not the latter.
> The ICZN doesn't care about nomina dubia. It cares about nomenclature, not
> about taxonomy. In fact, the only two times it mentions the term "nomen
> dubium", it says neotypes should be proposed for such names -- something
> that has never been done for a Mesozoic dinosaur.
> If *Titanosaurus* is not diagnosable, that doesn't automatically mean that
> Titanosauridae is undiagnosable, too; as long as *Titanosaurus* can still be
> referred to Titanosauridae on morphological evidence, Titanosauridae does
> not suffer at all.
Whether *Titanosaurus* is valid or not has no impact on the validity
of Titanosauridae, providing the former has been published in
accordance with the Code. By definition, Titanosauridae includes
*Titanosaurus*. This is the same problem for Hadrosauridae, and
Ceratopsidae (and other related names): they are based on dubious
species (well, today, at last). Which means that they can not be used
as specifiers of the clade names that they define (!). Which means
that all these names should *naturally* be considered invalid as long
as their respective type taxon/specimen is considered as invalid too.
Let's say I erected a taxon A with taxon B as a type/specifier. If B
is now considered as invalid, THEN A is invalid too. It would be a
complete nonsense to retain A in this case.
Fortunately, you have three possibilities if you encounter a nomen
dubium threatening an old-established (='stable') taxonomy:
1) request the deletion of this taxon to the ICZN (e.g.,
*Dynamosaurus*, *Rioarribasaurus colberti*)
2) request the transfer of the type status to another taxon (e.g.,
*Cetiosaurus) or specimen (e.g., *Allosaurus fragilis*, *Parasuchus
hislopi*, *Coelophysis bauri*)
3) change the taxonomy.
> To eliminate Titanosauridae, *Titanosaurus* would have to be a junior
> synonym or (I guess) a nomen nudum.
A such synonymy would change nothing as the Code deals only with rank
group synonymies. *Trematops milleri* Williston, 1909 was for instance
identified as a junior synonym of *Acheloma cumminsi* Cope, 1882 by
Dilkes and Reisz in 1987. It doesn't mean that the family name
Trematopidae Williston, 1910 is not valid anymore.
The family name Titanosauridae can be eliminated if its *Titanosaurus
indicus* is shown to be a nomen nudum or if the ICZN use its pleniary
powers to suppress Titanosauridae, *Titanosaurus*, or *Titanosaurus