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Re: Anchiornis huxleyi

On Fri, Sep 25, 2009 at 02:43:33PM -0700, Erik Boehm scripsit:
> Wouldn't one assume with feathers forming surfaces as shown in this
> fossil, that they did serve an aerodynamic function, and were under
> aerodynamic loads?

I think the absence of asymmetric remiges is a powerful argument that
the Anchiornis huxleyi was neither a powered flier _nor_ a distance

Contour feathers form aerodynamic surfaces, in the sense of providing
streamlining; I think it's perfectly plausible to suggest that a small
theropod with the feather pattern observed in this case derived benefit
from streamlining but not from exerting force through interacting with
the air.  (Or it benefited from a cryptic shape, or being able to make a
particular display in breeding season, or being able to look big, or bug
snaggers, or snowshoes, or something of that character as well.)

> And by "any kind of aerodynamic load produces it, absence of
> aerodynamic load means it goes away," Do you mean the trait goes away
> in species that don't experience aerodynamic loads (obviously, an
> Osterich doesn't have much need for asymmetrical feathers, and birds
> that fly have both symmetrical and asymmetrical feathers),


Note that you need a truly flightless bird to lose the vane asymmetry in
the remiges; flightless ducks will do the run-across-the-water thing,
with the wings providing thrust, for example, and so keep the asymmetric
remiges.  Really flightless birds like ratites and some rails lose the
asymmetric remiges.

I should certainly have said "any kind of aerodynamic load on a
thrust-producing bird wing", rather than the rather hasty version I did

> or do you mean that somehow the feather needs to be be exposed to
> aerodynamic forces at the individual level to become asymmetrical -
> Im fairly sure flight feathers start off asymmetrical long before
> exposed to aerodynamic forces, I'm just making sure I understand your
> statement clearly.

Flight feathers develop with the flight asymmetry whether or not the
bird is flying. (the Metro Zoo has a one-winged barred owl, and the
feathers of the remaining wing come in entirely suitable for flight, for
example.)  So, no, didn't mean this version; sorry for the lack of

-- Graydon