RE: Nomina Dubia Part II: Rapator

[Tim Williams <tijawi@yahoo.com>]

Michael Mortimer <mickey_mortimer111@msn.com> wrote:
 

> Even if that ulna shared characters with M. zhaoianus that
> were lacking in Sinornithosaurus, Graciliraptor, etc.?


Depends on the characters in question.  Are these ulna characters diagnostic 
for _Microraptor_?


> I think this is the crux of our disagreement, since if
> hypothetically Rapator did share genus-level diagnostic
> characters with Australovenator, I think you would agree
> with me that it isn't a nomen dubium.  


Definitely!  If these diagnostic characters were shared exclusively by 
_Rapator_ and _Australovenator_, then the latter would be sunk as a subjective 
junior synonym of _Rapator_.  No questions asked.


> They're never
> explicitly stated to be "genus-level diagnostic characters",
> but they are characters stated to distinguish genera
> (Rapator/Australovenator from Megaraptor) within
> Megaraptora.  


Yes these characters are used to distinguish genera... but are they good enough 
to formally *diagnose* genera?


> Does this not make them genus-level diagnostic characters?  


No.  Not automatically. 


> Take an analogy from
> Archaeopteryx again.  Both lithographica and siemensii
> have a posteriorly forked ischium, unlike Shenzhouraptor,
> etc..  That's a genus-level diagnostic character shared
> by them that lets us synonymize them if their differences
> aren't deemed to be taxonomically significant.  


If this character (forked vs non-forked ischium) is not taxonomically 
significant AND it's the ONLY character used to distinguish _Archaeopteryx_ 
from _Shenzhouraptor_.... then yes, we would synonymize the two.



> If you want to say that Agnolin et al. were
> wrong to claim these characters allow us to distinguish
> Rapator and Australovenator from Megaraptor, then I would
> agree that in that case Rapator would be a nomen dubium.


I say it's not so simple.  


We simply don't have enough evidence regarding the degree of morphological 
variation in metacarpal I within a megaraptoran species... so we can't be 
confident that 
acters allow us to distinguish _Rapator_ and _Australovenator_ from 
_Megaraptor_.  Until we do, it is safer to regard _Rapator_ as a nomen dubium.


Look, if the metacarpal I named _Rapator_ had been discovered last year, it 
almost certainly wouldn't have been given a name.  The only reason we're giving 
_Rapator_ so much attention is because good ol' Friedrich von Huene decided to 
give it a name back in 1932.  He shouldn't have, but he did.  He also shouldn't 
have bothered naming _Walgettosuchus_ either; but he did.  Huene loved to name 
things.  So these named specimens attract more attention than other isolated, 
fragmentary elements that were (thankfully) never named. 


I agree that we shouldn't be so ready to dismiss poorly known taxa like 
_Ceratops_ and _Rapator_ as nomina duba simply because they are founded on 
fragmentary material.  After all, some perfectly good taxa are based on single 
elements or fragmentary material - like _Xenoposeidon_ (hey, you out there 
Mike!)


But I think you're swinging to the opposite extreme Mickey.  We shouldn't have 
to pore over every nomen dubium based on a bone fragment or isolated element in 
the hope of gleaning characters that can be used to revive the name as a valid 
genus or species.  I think names like _Ceratops_ and _Rapator_ are toast not 
because paleontologists are too lazy to exhaustively examine the material, but 
because the claimed "distinguishing characters" are fairly dubious (at best).  
IMHO, these names (_Ceratops_, _Rapator_, etc) do not deserve the special 
pleading required to justify their usage as valid names.



Cheers

Tim