Re: Ornithomimus had feathers and "display" winglike forelimbs

[Tim Williams <tijawi@gmail.com>]

Gregory S. Paul  <GSP1954@aol.com> wrote:

> But ornithomimids did not have folding arms so they were not critical for
> protecting such irregular feathers.


Ornithomimids did not have a semilunate carpal (as I stated).  The
hypothesis I advanced is that a semilunate carpal came *after* the
advent of long, pennaceous feathers along the forelimb.  One or the
other had to come first - and if arm-folding was selected to protect
long forelimb feathers, then there is no reason why this ability
should *precede* the appearance of long forelimb feathers.  BTW, this
also holds true for your hypothesis (below) that folded arms were
selected to protect finely defined wing airfoils.


Although the folding mechanism bestowed by the semilunate carpal
('swivel-wrist') might not have been "critical" for protecting
feathers, it might nonetheless have been an asset in keeping long
feathers out of the way.  Especially for small theropods that lived in
dense forests.  There is no reason to assume that arm-folding *began*
as a flight-related feature...


> Folding arms are more selective for
> protecting finely defined wing airfoils.


Well, this is the case in modern birds.  However, you cannot assume
that this was the original function of arm-folding in theropods.  In
other words: like so many other components of the modern avian flight
apparatus, exaptation might have been important.


> And it is not known whether theropods as basal as or more basal than
> ornithomimids brooded their eggs.


Yes, this is still an open question.  AFAIK, phylogenetic bracketing
for evidence of brooding is limited to Maniraptora.  Nevertheless, the
fact that ornithomimids had wing-like structures (pennibrachia)
destroys the link between the evolution of long forelimb feathers and
aerial locomotion.





Cheers

Tim