Re: "Dinosaurs Died Within Hours After Asteroid Hit Earth..."

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Keesey wrote:

> Okay, *one* example you give is of convergence: tails with pygostyles 
> appear to
> have evolved twice, once within _Avialae_, and once within 
> _Oviraptorosauria_
> (although so far only known in _Nomingia_).

The basal therizinosauroid _Beipiaosaurus_ also has a pygostyle.  This 
feature may have evolved at least THREE times in maniraptoran evolution.

Interestingly, despite having a pygostyle, _Beipiaosaurus_ shows no evidence 
of a rectricial fan: the tail feathers attached to the pygostyle are not 
pennaceous (unlike _Caudipteryx_ and birds).

(Warning: Rampant speculation ahead...please take with a heavy dose of 
salt).  The only known _Beipiaosaurus_ specimen is not fully grown, so one 
could speculate that in certain non-flighted maniraptorans a pennaceous 
plumage only appeared with the onset of sexual maturity.  This was certainly 
not true for flying maniraptorans, since even the smaller _Archaeopteryx_ 
specimens are endowed with a full plumage, including the rectricial "frond" 
on the tail.



Tim

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