Re: Coelurosaur Phylogeny

["Tim Williams" <twilliams_alpha@hotmail.com>]

Dinogeorge@aol.com wrote:

> I may have defined Segnosauria as the stem-based clade way back in Mesozoic 
> Meanderings #2, only I had it as the sister group to Brontosauria in 
> Sauropodomorpha. That was when I considered segnosaurs to be 
> "prosauropod-derived." No big deal; we still don't know what it's the 
> sister group of in Theropoda (maybe Oviraptorosauria).


There's an enormous difference between putting the therizinosaurs (= 
segnosaurs) at the base of the Sauropodomorpha and putting them way up in 
the Maniraptora.  Analyses over the past 10+ years have been unanimous on 
this point.  _Beipiaosaurus_ provided hard evidence for the maniraptoran 
affinities for theriznosaurs and the recent discovery of _Incisivosaurus_ 
reinforces the close relationship between
oviraptorosaurs and therizinosaurs.

> Definitions come and go with each new cladification; difficult to take any 
> of them seriously.

The diagnosis and composition of a clade may change with new analyses.  
Definitions, by contrast, should remain intact; see Mike Keesey's posts.  
The reason they do not is because different authors offer competing 
definitions; this is not the fault of cladistics, per se.

BTW, "cladification" (and by that I guess you mean cladistic methodology) 
has a pretty good track record for elucidating relationships.  Sure, there's 
disagreement on where exactly compsognathids and tyrannosaurids and 
alvarezsaurids and therizinosaurs sit in the theropod family tree.  But 
overall, different analyses have reached a consensus that they all sit in 
the same part of the tree.  The precise branching order is contentious.

To paraphrase Tom Holtz, if you're looking for a definite answer, then 
science can only get you so far.  What science can get you is the best 
answer given the available data.  Beyond that point, you're in the realm of 
faith, not fact.





Tim

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