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Re: The ground-nowhere hypothesis on the origin of bird flight
On Thu, Oct 8, 2009 at 4:39 AM, Erik Boehm <firstname.lastname@example.org> wrote:
>> If nothing else, I think this explains why *Velociraptor*,
>> a clearly flightless animal, had wings with big quill knobs
>> which indicate that it was necessary to hold the wing
>> feathers in place against strong forces.
> But it doesn't explain why they would need feathered hindlimbs, as is
> apparent in that member of the troodon family they just found in the Jurassic.
This assumes that leg feathers are adaptive. Possible, but what if
they're developmental "spandrels"? What if the initial way that
maniraptors grew wings was by genes that effectively said, "Grow
large, stiff feathers on the limbs"? What if only later some evolved
inhibitors that said, "Reduce the feathers on the legs"?
Often when a new trait appears, it appears in great abundancy, and is
later narrowed down and refined by new inhibitors. Look at the
earliest "apo-pterygotan" insects, with 3 pairs of wings (one pair
significantly smaller than the other two), or the earliest
"apo-tetrapods", with 8 digits. The extra pair of wings/leg
remiges/three digits may not have been useful in and of themselves,
but may have been a side effect of evolving the other two pairs of
wings/arm remiges/the other five digits. Later the excess was trimmed
down in one or more lineages, and those tended to have greater
success, since they 1) didn't waste as many developmental resources
and 2) weren't carrying around unnecessary appendages.
Maybe this isn't the case, but it seems like something to consider.
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies