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feather symmmetry




On Thursday, September 12, 2002, at 02:30 AM, Rob Gay wrote:

Couldn't you base those measurements off of the isolated feather?
Peace,
Rob
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...

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.