Re: Jeholornis

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

Brad McFeeters <archosauromorph2@hotmail.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.



Tim

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