RE: Nomina Dubia Part II: Rapator

[Michael Mortimer <mickey_mortimer111@msn.com>]

Tim Williams 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_?

>From my perspective, any character found in Microraptor but not in any of its 
>closest relatives (and thus not something caused by individual, taphonomic or 
>ontogenetic variation) is by definition diagnostic for Microraptor.  You 
>apparently view the concept of 'diagnostic' differently based on your 
>subsequent statement...

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

So I must ask, when is a character that distinguishes a taxon from its closest 
relatives not diagnostic?  Especially since you said you allowed unique 
combinations of characters to be diagnostic, so even a plesiomorphy could be 
diagnostic if it's present alongside a synapomorphy.

> 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.

Well there you go.  You're saying that you're not confident one of Agnolin et 
al.'s statements is correct.  Yet my point required us to assume it was 
correct.  So really we agree conceptually about nomina dubia and that IF they 
were right in saying "Rapator and Australovenator are clearly distinct from 
Megaraptor" then they were wrong to call Rapator 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 actually disagree that Huene shouldn't have named it, assuming Agnolin et 
al.'s statements about it are correct.  After all, it was diagnostically 
different from any other theropod known at the time.  In fact, if Agnolin et 
al. are correct that Australovenator is more similar to it than to Megaraptor, 
Rapator's characters would even allow us to refer new material to it (whether 
or not it's distinct from Australovenator).  If Agnolin et al. and Molnar 
(1990) are correct about Walgettosuchus though, then indeed Huene should not 
have named that genus.

> 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.

Believe it or not, I'm actually a lumper.  After examining the Archaeopteryx 
(including Wellnhoferia) and Microraptor (including Cryptovolans) cases in 
depth, I concluded it was best to use only one species for each.  Basically 
every specimen is different in some way, and faced with the possibility of 
having several contemporaneous species in each genus represented by only one or 
two specimens each, I'll go with a single individually or ontogenetically 
variable species.  I've also agreed some taxa are indeed nomina dubia after 
examination- Chingkankousaurus, "Ornithocheirus" hilsensis, "Megalosaurus" 
lonzeensis, etc..  I might end up agreeing with you about Rapator.  Like I said 
in the beginning, I have no actual opinion on it at the moment.
 
Mickey Mortimer                                           
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