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RE: Nomina Dubia Part II: Rapator



Tim Willians 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.

No, my point is that the situation is the same for these taxa as for Rapator.  
Microraptor gui has a prominent biceps tubercle on the ulna and a fused 
sternum, etc. but are these enough to distinguish it from M. zhaoianus?  
Archaeopteryx siemensii has no pedal flexor tubercles and no cuppedicus fossa, 
etc. but is that enough to distinguish it from A. lithographica?  Rapator has a 
ventrally extended medial condyle and straight lateral distal condyle, etc. but 
is that enough to distinguish it from Australovenator?  These all have features 
that potentially let them be diagnosed as different species/genera.  I happen 
to think the features of M. gui and A. siemensii are just individual variation, 
but that doesn't make them nomina dubia to me, it makes them synonyms of M. 
zhaoianus and A. lithographica.  It's the same with Australovenator.  If its 
differences from Rapator turn out to be individual variation, then it would be 
a junior synonym of Rapator, not a nomen dubium.

>> 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.

And they also said "albeit being very similar in morphology, Rapator and 
Australovenator are clearly distinct from Megaraptor", which makes their 
statements somewhat contradictory.  Just another reason not to trust general 
unquantified statements like that when it comes to how distinct taxa are.  My 
point is that the metacarpal characters that distinguish Australovenator from 
Megaraptor serve equally well to distinguish Rapator from Megaraptor- "the 
presence of a more dorsoventrally developed mediodistal condyle and a lateral 
facet for articulation with the metacarpal II lying in almost the same plane as 
the lateral margin of the shaft."  These are thus genus-level diagnostic 
characters of Rapator as much as they are genus-level diagnostic characters of 
Australovenator.  To say they count for Australovenator but not Rapator is just 
a bias for the more complete specimen.

>> 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.

Er... why don't the features that differ from Megaraptor qualify?
As for Rapator being the more fragmentary specimen, that doesn't matter one bit 
for nomen dubium purposes.  A. lithographica's holotype (the skeleton, not the 
feather) is much less complete than A. siemensii's, but lithographica still 
gets priority because it was named first.
 
Mickey Mortimer                                           
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