Re: Tetanurae

[Michael Mortimer <mickey_mortimer111@msn.com>]

Tim Williams wrote-

> I disagree.  I think adding an abelisauroid as an external specifier is a 
> great idea.  Sereno added _Carnotaurus_" to ensure the stability of the 
> taxonomic content of the Tetanurae".  The revised definition succeeds on 
> this point, and is much better in this respect than having only 
> _Ceratosaurus_ as the external specifier.
>
> Although Gauthier (1986) was the guy who erected Tetanurae (and resurrected 
> Ceratosauria), abelisaurids (collectively or individually) had not yet been 
> exposed to a cladistic analysis.  _Indosaurus_ and _Indosuchus_ might have 
> been classified as tetanurans by Gauthier, but he also treated 
> tyrannosaurids as carnosaurs.  These were all a priori assumptions made by 
> Gauthier, and not actually tested.
>
> Paul's (1988) classification of theropods was not cladistic.  But if, for 
> example, a cladistic analysis does recover abelisauroids as the sister 
> taxon to carcharodontosaurids (as has come up), then Tetanurae would 
> certainly contract (and would probably be equivalent in content to 
> Neotetanurae!).  So much for "taxonomic stability".  But I would regard an 
> abelisaurid+carcharodontosaurid clade as a remote (but exciting) 
> possibility.

I suppose the difference is that for stem-based clades, I value the idea of 
the clade more than the content of the clade.  "This clade specifies this 
idea, and let the taxa fall where they may" etc..
Is a (Ceratosaurus(Abelisaurus,Ornithomimus)) topology really likely enough 
to validate using an abelisaurid external specifier for Tetanurae?  I don't 
believe it's occurred in any published analysis.

Mickey Mortimer