Theropod polyphyly vs BCF

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

George wrote:

> I think what he is arguing is that the theropod bauplan evolved several 
> times
> independently in nondinosaurian archosaurs, and that we're lumping all 
> these
> lineages into Theropoda because of their homoplasies. This isn't BCF, since
> BCF assumes dinosaurian and theropod monophyly.


My response was somewhat tongue-in-cheek.  Yep, what he is saying that the 
bird-like theropods are more closely related to _Longisquama_ than to other 
theropods, and most of the similarities are due to convergent evolution 
between two independent lineages.  The former lineage was favored to survive 
into the Cretaceous as a result of some end-of -Jurassic "minor holocaust" 
(an oxymoron?).  The "dogma", of course, is that the Theropoda is 
monophyletic.

The similarity to BCF is that an arboreal _Longisquama_-like ancestor gave 
rise to ground-dwelling bird-like theropods.

Personally, I'm ready to believe that many Cretaceous maniraptorans may have 
evolved from a volant pre-archaepterygid theropod (which would explain the 
feathers in _Caudipteryx_ -it's secondarily flightless).  But the fossils we 
currently have available don't support that hypothesis.


Tim

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