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RE: Nomina Dubia Part II: Rapator
Michael Mortimer <firstname.lastname@example.org> 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
> 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
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
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
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.