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Re: flying Archie

On Sun, Sep 24, 2006 at 04:54:30AM -0700, James R. Cunningham scripsit:
> Graydon wrote:
> > What we've got is an environmental disjunction, with pronounced
> > bottlenecking across the boundary.  If the archie-style fliers
> > continued to prosper up to that disjunction, presumable what we've
> > got is a combination of bad luck and the environments for which the
> > long-tailed flight style was preferable not being available for a
> > time as a result of that disjunction.  (and all it has to be is long
> > enough to starve to death, as per Jim Cunningham's pterosaur
> > extinction hypothesis.)
> There is an alternate hypothesis in the case of birds.  Let us presume
> a modification of the brain that reduces the need for flight
> stability.  That reduces selective pressure to maintain the long,
> draggy old-style tail (which was an asset before the brain
> modification).  Consequently, the tail will become more variable with
> some being shorter.  That increases maneuverabilty and the potential
> for prey capture, or food acquisition by whatever means.  That
> increases selective pressure to maintain the shorter tail, and that in
> turn increases selective pressure to be able to move that shorter tail
> in ways that generate tail moments (command authority).  Presto, ain't
> too long before you've got pygostyles and long tails have gone by the
> wayside.  That, in turn, opens up an avenue that allows redevelopment
> of long tails based on the modern style, for display purposes.

Don't we see (incipient) pygostyles in various oviraptosaurs which are
not suspected of coming from a volant lineage?

The hypothesis as given makes a lot of sense, and clearly the short tail
has to have had selective advantage in some context or it wouldn't have
persisted after it arose by whatever means, but I don't think it's a
testable hypothesis in a paleontological context, since it depends on
actual neurons, not the gross anatomy of the brain.

I'm also uncertain that directional stability, even at the expense of a
long, draggy tail, is a disadvantage in all niches; is it established
that the tradeoff is obvious in cases where there's a lot of turbulent
air or there's food capture through diving or, perhaps, high speed

I can easily see the short tail being better in many situations; it's
"better in all situations" that's making me dubious.