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Re: Pygostyle



>Actually, it supports the bird->flightless theropod model. The oviraptorosaur 
>(if that is what it belongs to!) pygostyle is best explained as a feature 
>acquired as a flight adaptation that was retained in the ground-dwelling 
>descendant form.

The NG article suggests that the pygostyle may have evolved to support the
tail fan for display purposes.  In fact, if Caudipteryx, which does not
have a pygostyle (correct?) is a basal oviraptorian and the form with the
pygostyle is a more derived one, this would suggest that the pygostyle (at
least in Oviraptoria) is a derived condition that appeared after the
evolution of the tail fan.  If this interpretation is correct, then the
pygostyle in this group cannot be a retained adaptation from a flying
ancestor - and, perhaps, this means that the pygostyle was independently
developed in oviraptorians and Aves.  

I would wonder, in fact, if a pygostyle supporting a tail fan at the end of
a more or less flexible tail is of much aerodynamic use, though I can
certainly see its usefulness in display.  If I am on the right track here,
then the pygostyle could not have evolved for flight, as it would not have
been too useful until fusion of the tail vertebrae was almost complete -
but I'll yield to the aerodynamic experts on this point!  Nonetheless, I
think you could use the pygostyle-bearing oviraptor to argue the exact
opposite of what George is suggesting.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
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Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com