Re: terminology

[David Marjanovic <david.marjanovic@gmx.at>]

>  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 (!).

Not true. A specifier doesn't need to be distinguishable from other 
species (whatever a species is) in the clade the name of which it is 
supposed to define; it only needs to be identifiable as a member of that 
clade and as not a member of other clades.

The PhyloCode doesn't use the term _nomen dubium_ either.

>  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.

Nomina dubia are not invalid under the ICZN; and "undiagnostic" is a 
matter of degree, not an either-or thing. (For instance, any fossil bone 
fragment obviously comes from a vertebrate and is therefore allowed to 
be a type specimen or specifier for Vertebrata.)

>  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.

Article 75.5 strongly recommends 2). That's why the attempt to solve the 
*Coelophysis* situation in way 1) was rejected by the ICZN in favor of 2).

>  To eliminate Titanosauridae, *Titanosaurus* would have to be a
>  junior synonym or (I guess) a nomen nudum.

Sorry!!! I meant homonym, not synonym.