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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
--- On Sat, 9/27/08, Michael Habib <firstname.lastname@example.org> wrote:
> Familiarity does not equate with applicability. Besides, I
> never said
> exclusion was unimportant (in fact, I stated the opposite).
OK. I note that reality is highly applicable, and move on.
> Not true - mechanical constraints are often easy to
> quantify, are very
> dependable metrics for certain problems, and have been
> convincingly to be a major aspect of biological evolution
> both in
> modern populations and through evolutionary history.
Not to the point of falsifying a gliding-to-powered scenario. That was the
assertion (or at least implication), remember? Remarkable it was, considering
the consensus on bats.
> Yes, sometimes expectations are not met. If you can
> demonstrate where
> I (and others) have made an error regarding the expected
> breakdown of
> vorticity from flapping in most obligate glider planforms,
> then go for
> it. The fluid dynamic equations are pretty robust, though.
I already pointed out the error, which is failing to consider the various
points of various glide sequences at which selection on incipient flapping can
occur. Nothing to do w/ falsifying equations.
> > No flying squirrel will ever increase glide length by
> waving it's paws
> > in mid-flight, but it is possible for selection to
> enhance control
> > motions that occur at the end of the glide.
> Quite possible. There are also possibilities related to
> launching, and prey capture that could introduce flapping
I never said or implied there weren't other possibilities. Quite the opposite,
as you surely know.
There was been an attempt to falsify (or at least dismiss) the possibility (or
likelihood) of a glide-to-power sequence in birds, largely on the basis of a
perceived lack of arboreal ancestry, bolstered by claiming that extant gliders
show no sign of evolving powered flight.
I merely pointed out that small terrestrial bipeds could easily exploit the
morphology of cycads, positioning themselves for a gravity-driven first step,
and that the 'lack of flapping' in extant gliders was easily explained by
> also quite possible that ancestral bats differed in
> critical details
> from flying squirrels, in terms of planform and airfoil
I would bet on it. The point about selection acting on incipient flapping at
specific points in the glide event still stands, however.
> Question: if you were going to attempt to falsify an
> arboreal origin
> for flight in a given group, how would you go about it?
I wouldn't. Way too hard.
> Your argument
> that Archaeopteryx could maybe, possibly climb things and
> use them for
> elevated leaps is fine - but it's also a sort of
> special pleading.
I disagree. Besides, my argument is that Arch. (or more to the point Arch.
ancestors) could _definitely_ climb certain tree species (ie, they were not
"mechanically constrained" from it), and those trees were common. Physical
capacity does not certify behavior, of course.
> outgroups to birds are terrestrial, the most basal birds
> appear to have
> limited arboreal adaptations (if any),
Again, this does not falsify gravity-driven evolution, particularly
'first-step'. Teeth and four sets of claws will get you up a cycad. This opens
lifestyle possibilities that are open-ended relative to various "mosaics" as
you call them. The lack of extreme arboreal optimization actually greatly
improves the initial position relative to achieving powered flight, logically
(once they are up in the tree, I mean).
> and birds have
> several exapted
> traits that could make terrestrial launch possible
Well, birds are the end result of the process, aren't they?