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Re: 11th specimen of Archaeopteryx
On Oct 30, 2011, at 12:40 PM, Don Ohmes wrote:
> The density of the flight medium does indeed limit wingloading at given
> speed w/ given design specs -- what amazes me is that many people reject
> the idea that living fliers will alter their morphology in predictable
> ways over time to adapt/optimize to a given density or range of densities.
Not sure who rejects that, but animals certainly make adjustments for density
changes. However, one of the easiest, particularly for larger vertebrate
flyers, is simply to adjust speed. Geese at high altitudes do not appear to
change their wing shape much, for example - they probably just speed up. In
other taxa, slight changes in wing shape are typically sufficient. Insects,
which do not have morphing wings in the same way that a bird or bat does, are
more constrained in that regard.
> But to get back on topic -- 1) models are very nice, but there is no
> need to speculate on how a lack of inboard feathers affects performance.
> It should be investigated empirically.
I generally agree, but add the caveat that empirical measurements of inboard
gaps in living birds is somewhat confounded by their possession of a derived
flight morphology. Empirical measurements of life-sized Archie models would
suffer from the problems of static position assumptions. So, while it should
be investigated empirically, we still need the math, too (in part because it
provides a null model expectation).
> 2) 'turning/agility scenarios' are weak in my view because although
> mathematically significant forces may be generated by proto-wings in
> "terrestrial" scenarios -- even in the absence of a full upstroke --
> they cannot be applied in timely fashion. Even in humans stride
> frequencies are 3 or 4 steps per second, and in posited pre-birds would
> be much higher. Air being compressible, and circulation slow to build,
> it is much quicker and much more economical to simply plant one foot and
> change direction.
Point taken. However, circulation can be built many times faster with brief,
but intense, accelerations. As a result, engaging a wing to turn at the same
time that a foot is planted and pushing off should be able to successfully
improve the turning radius, particularly if the wing is rapidly translated at
> 3) nor do I see fighting scenarios as compelling, in the absence of a
> full upstroke -- no boxer draws his hand back behind his head to strike
> a blow -- so where does incremental selection toward a full upstroke
> come from?
> You may wonder why people want to "put Archie into trees", but given
> that: a) no terrestrial animal that is physically able to work it's way
> into a tree, yet does not occasionally do so comes readily to mind -- I
> have observed turtles, alligators, dogs, foxes, goats, leopards, lions,
> bears, rats, coons and 300 lb rednecks in trees at various heights and
> comfort levels -- b) "perching adaptions" are only useful on small limbs
> -- most plants over 3m in height have limbs large enough to sleep on,
> and c) Archie-types had claws fore-and-aft plus teeth, and so could
> indeed climb, however laboriously.
> So I wonder why the drive to make poor old Archie sleep on the ground.
> It seems dangerous to me, and run-around-on-the-ground, sleep-in-trees
> lifestyles seem to be popular even today.
I understand the argument, but that same line of reasoning could place a huge
variety of fossil forms in the trees form time to time. While that is probably
not altogether inaccurate, it is not a compelling argument for a heavily
arboreal-oriented model of flight evolution. That said, your idea of trees as
a refuge is considerably more robust than most of the arboreal models. I like
your list of terrestrial climbers, btw. Particularly the 300 lb redneck. They
just get into everything, don't they?
Assistant Professor of Biology
Woodland Road, Pittsburgh PA 15232
Buhl Hall, Room 226A