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Re: four winged Archaeopteryx
On Fri, Sep 29, 2006 at 11:53:53AM -0700, Jaime A. Headden scripsit:
> Graydon (firstname.lastname@example.org) wrote:
> >All known birds can fluff their insulative feathers, and it's very hard to
> >how a non-mobile insulative structure could survive selection pressure, so
> >least hypothesis is that the proto-feather could move. Not a lot, but there
> >would have to be some mechanism to raise and lower it to control the amount
> >trapped air. [...] Since an _immobile_ aerodynamic feather doesn't make sense
> >from an aerodynamic standpoint, evolving from a mobile insulative feather to
> >immobile aerodynamic feather is a very strong claim. [...] What the mobility
> >mechanism was we don't know, and probably cannot know, but the idea that
> >necessarily wasn't one at all is an awfully strong claim.>
> The very premise that skin-muscles, which are used to fluff the hairs on
> arm or the feathers on a birds breast, can be used to analogize the spreading
> of wing or tail feathers, which are otherwise anchored in ligaments and
> that have rather strict motions concerned their movement, is also about as
> strong as a claim as I making the opposite.
But I didn't make that claim. I made the claim that evolving from
mobile insulative to immobile aerodynamic was a very strong claim.
What got exapted or what evolved to provide what degree of mobility to
the aerodynamic feathers is an outstanding question, and maybe not an
answerable question, but proposing an immobile aerodynamic feather _and
expecting to work for flight_ is a very strong claim.
> Neither have any evidence to back them up, and thus both appear
> equally likely. My premise that skin-muscles which could be used for
> this purpose are NOT the ideal null hypothesis for the condition
> advocated is based on the argument that the skin-muscles for feather
> movement are an exaptation IN birds, and do not neccessarily precede
> them, and they should NOT be considered present in the tail without
> any evidence FOR the case. This doesn't mean I am saying they DO NOT
> exist, but that there is no evidence to presume they do except the
> fancy that Archie -- like birds -- has this ability. That idea is
> based only on the archetype that as a bird, it should do everything a
> bird can do. Romantic, to say the least.
If you accept that Archie could fly, you're accepting that the tail
wasn't a single rigid surface.
_In what way_ it wasn't a single rigid surface remains a very good
question, but it couldn't have been completely immobile if Archie could
Now, maybe you think Archie couldn't fly, but if so, you seem to be
making the claim that no bird could until pygostylians, which seems
pretty strong, too.