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RE: Nomina Dubia Part II: Rapator

Michael Mortimer <mickey_mortimer111@msn.com> wrote:

> My issue with that is that a species of uncertain validity
> vs. another is NOT a nomen dubium.  Or else we'd be
> calling Archaeopteryx seimensii, Wellnhoferia, Cryptovolans,
> Microraptor gui, Nanotyrannus, etc. nomina dubia.  But
> nobody does this.  They're merely labeled as junior
> synonyms or valid species, depending on the author. 

This is because the respective holotypes of these taxa preserve characters that 
allow them to be diagnosed at the level of genus or species.  So they cannot be 
nomina dubia.  

> Another point against calling Rapator a nomen dubium because
> of this is when you have two or more taxa that may be
> synonyms, which one gets to be the nomen dubium? 

The specimen that is based on non-diagnostic material (at the genus or species 
level) is the nomen dubium.

> Rapator is just as distinctive as Australovenator according
> to Agnolin et al. and has decades of priority. 

Well, this is not exactly what Agnolin et al. said, or even implied.  They 
actually state: "In particular, the morphology of metacarpal I in _Rapator_, 
_Australovenator_ and _Megaraptor_ is almost identical."  True, what follows is 
a description in which the Agnolin et al. distinguish _Rapator_ and 
_Australovenator_ on the one hand (so to speak) from _Megaraptor_.  But Agnolin 
et al. never actually recognize any genus- or species-level diagnostic 
characters in the metacarpal I of _Rapator_.  That's what makes _Rapator_ a 
nomen dubium.

> Shouldn't Australovenator be the questionably valid name
> since it was based on a specimen that could not be
> definitely distinguished from a previously named taxon?

No, because in the opinion of Agnolin et al. the holotype of _Rapator_ has no 
genus- or species-level diagnostic characters.  Thus, the specimen can only be 
assigned to the level of Megaraptora (i.e., it is "Megaraptora indet.").  

So, although _Rapator_ and _Australovenator_ share unique features in common 
with respect to the morphology of metacarpal 
., these shared features do not qualify as genus- or species-level diagnostic 
characters.  Because _Rapator_ is known only from an isolated metacarpal I, it 
is a nomen dubium.