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Re: Greg Paul is right (again); or "Archie's not a birdy"



Jason Brougham <jaseb@amnh.org> wrote:

> My point is precisely as you have suggested: Xu's new topology leaves it 
> unclear whether the last common ancestor between Archaeopteryx and birds was 
> volant or engaged in any aerodynamic
> behaviors at all.


Pennaceous remiges and/or rectrices are present in non-paravians such
as _Caudipteryx_, _Similicaudipteryx_, and _Protarchaeopteryx_.  The
presence of what has been called a 'pennibrachium' by Sullivan et al.
(2010) (a forelimb bearing long feathers that form a planar, wing-like
surface) is primitive for a more inclusive clade than Paraves.  As
Sullivan &c point out, these pennibrachia might originally have had no
function at all in aerial locomotion - although by Paraves (at the
latest) it is almost certain that pennibrachia (wings) were used for
some form of aerial locomotion.  That means that if _Epidexipteryx_ is
an avialan, its lack of pennibrachia is secondary, although the
forelimbs were not truncated.  Curiously, _Caudipteryx_ had short
forelimbs (by maniraptoriform standards), but retained pennibrachia.


Whether the last common ancestor of _Archaeopteryx_ and birds was
volant (or engaged in any aerodynamic behaviors at all) depends on if
pennibrachia evolved for some form of aerial behavior.  I suspect that
they did.  As the ancestors of birds were likely herbivores, I picture
them scaling the trunks of cycads, plucking the nutritious seed cones
at the apex, then using gliding to return to the ground safely.  I've
probably mentioned this before, so apologies for any repetition.


> When you suggested that Epidexipteryx looks secondarily flightless I wanted 
> to point out that it could look primitively flightless as well, given a 
> different hypothesis.


_Caudipteryx_ has been the subject of a similar debate.  I side with
the view that its ancestors were gliders, but that _Caudipteryx_
itself had lost any aerial abilities.





Cheers

Tim