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feathers



I noted a while back the similarity of feathers to the branched structures
which are used by plants to parachute their seeds (thistle down and
whatnot). At the time I was of the belief that feathers (albeit
ratite-like ones) originally evolved for insulation, but in light of some
skepticism about branching in the insulatory structures of Sinosauropteryx
(assuming it does have insulation) I'm a little more open to looking at
this. 
    Basically, it seems to me that these downy seeds are the only example
of convergent evolution of a feather-like structure (at least that I know
of)- i.e. a central rachis with barbs branching off. And I wonder if this
argues (however circumstantially) that the branching of feathers evolved
for aerodynamics, not insulation, although perhaps the feathers started
out as insulatory bristles/hairs without secondary branching. Something to
think over...