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RE: Nomina Dubia Part II: Rapator



Tim Williams wrote-

>> 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?
>
> In all three cases (_Microraptor, _Archaeopteryx_, _Rapator_) I would say 
> "perhaps not". However, for _Microraptor gui_ and _Archaeopteryx siemensii_ 
> there are enough characters (apomorphies) elsewhere in the skeleton to 
> justify referral to _M. zhaoianus_ and _A. lithographica_ respectively as 
> junior synonyms.
>
> But if _M. gui_ was known *only* from an ulna, and its only diagnostic 
> character was the more prominent biceps tubercle, _M. gui_ would probably be 
> a nomen dubium.

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

>> 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.
>
> No, I think you're reading too much into the qualitative descriptions given 
> by Agnolin &c. Never are these characters explicitly stated to be genus-level 
> diagnostic characters.

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.  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.  Does this not make them genus-level diagnostic characters?  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.  Rapator and 
Australovenator both have a lateral facet for articulation with the metacarpal 
II lying in almost the same plane as the lateral margin of the shaft, unlike 
Megaraptor, etc..  That's a genus-level character shared by them that lets us 
synonymize them if their differences aren't deemed to be taxonomically 
significant.  What more would you need for them to count?  Do you require 
someone to list the features in a genus' official diagnosis for them to have 
meaning, or to state "character X is an apomorphy of genus y"?  Remember, I'm 
not arguing for their actual quality or validity.  They could be caused by 
distortion or individual variation for all I know.  I'm just saying that 
assuming Agnolin et al. are correct in stating they allow Rapator and 
Australovenator to be distinguished from Megaraptor, the rest of my arguments 
follow.  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.

Mickey Mortimer                                           
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