Re: Tetanurae

[Tim Williams <twilliams_alpha@hotmail.com>]

Mickey Mortimer wrote:

> As an aside, I don't agree with Sereno's revision of Tetanurae's 
> definition, adding Carnotaurus.  As I wrote previously-The addition of 
> Carnotaurus as an external specifier by Sereno (2005) seems 
> counter-productive. Tetanurae was designed as a stem away from 
> Ceratosaurus, and abelisaurids were not explicitly discussed (having been 
> named only a year prior). In fact, technically, Indosaurus and Indosuchus 
> were classified as tetanurines by Gauthier (1986), since he lists them as 
> carnosaurs. If abelisaurids are megalosauroids (as in Paul, 1988), it 
> shouldn't stop megalosauroids from being tetanurines.

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.

Cheers

Tim

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