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On Thursday, September 12, 2002, at 02:30 AM, Rob Gay wrote:
Yeah... but I think the problem is the precise degree of asymmetry is
dependent on the position of the feather among other things... and it's
hard to tell which feather it is... unless you infer the position from
the asymmetry. Which of course is a bit circular. It's clear that the
vanes *are* asymmetrical in _Archaeopteryx_ but *how* symmetrical is
hard to tell. The London specimen has the feathers splayed out quite a
bit I think, but again you'd have to be very careful in reconstructing
the wing to figure out which feather was where in order to make reliable
inferences. There are other problems- Archaeopteryx has maybe three
(?four) feathers making up the leading edge of the wing whereas most
modern birds have just one primary forming this edge; so directly
comparing primary 1 of Archaeopteryx to primary 1 of a seagull or
whatever might not be realistic...
Couldn't you base those measurements off of the isolated feather?
re: symmetrical flight feathers, yes you could do this; it'd be
suboptimal and likely need either a larger diameter shaft and/or shorter
feathers, or feathers directed posteriorly to reduce the torsional
loading, to work very well. On the other hand, I can't see why an
asymmetrical arrangement should be so difficult to evolve, and if they
are being extended out into an airstream, there should be a selective
pressure for asymmetry. If anything asymmetry might predate actual
powered flight since the retrices, which are held steady rather than
flapped, have asymmetrical vanes, and lift-producing structures in
general tend to be asymmetrical in their support systems (e.g. grebe toe
winglets). Anything other than the most rudimentary form of flight I'd
expect to see asymmmetry in.
Another interesting thing with respect to flying vertebrates... I
was looking at some molossid bat skins recently, they are very cool.
Molossids have extremely long, narrow wings and apparently use speed
more than maneuverability to catch insects. Interestingly, in the
particular specimens I was looking at, the wing membrane ends roughly at
the knee! Anyways its sort of interesting re: the "knee vs. ankle"
argument on pterosaurs... either reconstruction of the wing membrane is
arguably "batlike" depending on which bats you are talking about, and
naturally its quite possible that multiple different arrangements
existed in the diverse pterosaurs. Uropatagia are also structurally very
diverse in bats.