feather symmmetry

[longrich@alumni.princeton.edu]

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.