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