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Re: Anchiornis huxleyi

On Sat, Sep 26, 2009 at 08:28:20AM -0600, jrc scripsit:
>> I think the absence of asymmetric remiges is a powerful argument that
>> the Anchiornis huxleyi was neither a powered flier _nor_ a distance
>> glider.
> Why so?  Note that I'm not saying that Anchiornis was either/neither, 
> just questioning your assumption.

Well, there are a couple-three assumptions.

First -- that the developmental mechanisms of vaned "true" feathers are
essentially the same whether the feather is being grown in the mesozoic
or modernly.  So there isn't a feather development mechanism missing in
the mesozoic examples of vaned feathers the would prevent the
development of asymmetric feathers, nor one that would make feather
shape difficult to select for.

Second -- that the range of powered flight regimes available to anything
descended of a maniraptoran theropod are such that the modernly observed
ubiquity of asymmetric remiges isn't a side effect of an un-represented
powered flight regime.

Given that, the modern ubiquity of asymmetric remiges on birds that
generate thrust with the wing, or which are recently descended from same
 and which still glide (Kakapo, for example), looks to me like an
argument that a thrust-generating wing produces selection pressure for
asymmetric remiges.

-- Graydon