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Re: tiny-armed theropods



Anthony Docimo <keenir@hotmail.com> wrote:


> On the other hand, if you make up a name that you think all Coelophysids and 
> Podokesaurids can be grouped together within  (say,
> Gdayraptoroidea), that might also prove labile if the features you assign it 
> (based on the Coelophysids and Podokesaurids and anyone
> else you group with them at the time) turn out to be not what  you 
> thought...such as if _Coelophysis_ belongs outside the group, far away
> from _Podokesaurus_.
>
> Would the Gdayraptoroidea have to be scrapped?


I might not be fully understanding you here, but here goes...


(1) Coelophysoidea is tied to _Coelophysis_.  Podokesauroidea is tied
to _Podokesaurus_.  If _Podokesaurus_ is not a member of the clade
Coelophysoidea (defined as _Coelophysis_ but not _Ceratosaurus_,
_Carnotaurus_ or _Passer_), then there is no problem.  But if
_Podokesaurus_ is inside Coelophysoidea then the ICZN would say we
have to re-name this clade Podokesauroidea.  I say this is silly,
because Podokesauroidea has no phylogenetic definition - and we
shouldn't have to provide it with one just for this contingency.


(2) Those "features you assign to it" constitute the diagnosis, not a
definition.  Unless you're advocating an apomorphy-based definition of
Gdayraptoridae (and I don't think you are), the definition of
Gdayraptoridae would be linked to specific taxa, such as _Coelophysis_
and/or _Podokesaurus_.  Thus, the content of Gdayraptoridae would
depend upon how you define this clade.  For example, if you were to
define Gdayraptoridae as "all descendents of the most recent common
ancestor of _Coelophysis_ and/or _Podokesaurus_" then the content of
Gdayraptoroidea would depend upon the relative position of
_Coelophysis_ and/or _Podokesaurus_ within a cladogram.


(3) Because there is currently no genus Gdayraptor or family
Gdayraptoridae, the group Gdayraptoroidea is NOT a coordinated
family-level taxon.  Thus, Gdayraptoridae does not fall under ICZN
rules.  Coelophysoidea and Podokesauroidea, on the other had, do.





Cheers

Tim