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Brad McFeeters <email@example.com> wrote:
Should that be said about _Archaeopteryx_ when _Jeholornis_ is clearly a
side-branch? Which tail shape allows for better flight ability?
A good question. One hypothesis is that the long tail, equipped with
feathers down its length (a rectricial "frond"), acted as a sort of "third
wing" in the early stages of flight evolution - at least as exemplified by
_Archaeopteryx_, _Jeholornis_ and _Rahonavis_. As the flight ability of
birds progressed, the tail's role in generating lift diminished. Thus, the
tail skeleton became shorter, by fusion both proximally (with the synsacrum)
and distally (as the pygostyle), and the tail feathers formed a rectricial
fan. Steve Gatesy has done a *lot* of interesting work on caudal functional
anatomy in theropods, up to and including birds.
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