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Re: The origin of flight: from the water up
David Marjanovic wrote:
> > Why would a
> > semiaquatic bird *want* large wings?
> Because it still needs them for other purposes, such
> as brooding. Unlike a
> penguin. Big wings mean more room for eggs which in
> turn means either bigger or more eggs which in turn
> means more surviving offspring. It's a very
> simple case of natural selection.
However, the parent(s) must nourish their offspring.
If you have many mouths to feed, you better be a good
swimmer to catch the food necessary to ensure the
survival of all the chicks. Otherwise, you'd be
wasting energy on long wings and more eggs than you
can take care of. In other words, why have long wings
for brooding if they make it difficult to feed your
progeny? If anything, evolution will favor a smaller
brood or egg size and smaller wings.
Regarding the problem of buoyancy:
> When the theropods specialize in this behavior
> instead of staying more generalistic... like a
> dipper. AFAIK dippers are as extremely pneumatized >
as any passerine, and much more than a basal
They also have to grip the river bed and can only stay
under for 30 seconds. In the web pages I've visited
looking for more information on this bird, it says
they have stubby wings - just what I'd expect. It
probably isn't as good a flier as other small
songbirds, as a result. It's also pretty telling that
birds like brown pelicans have to plunge-dive from 60
feet above the surface.
> I don't know anymore whether I've seen that on TV,
> but Feduccia mentions many species of auks and
> petrels that fly straightly through waves. Haven't
> seen lots of dippers on TV.
Maybe they simply fold up their wings and shoot
> > We already have nicely feathered arboreal
> > maniraptors.
> Arboreal? Do we? Except for the aye-aye analog which
> may be very close to Pygostylia (I won't say why I >
think so, and my evidence is very limited anyway)?
I disagree, and I won't say why I think so either.
_Microraptor_, while it's halluces may not be
reversed, could have climbed trees. IIRC HP Mickey
Mortimer said new specimens show a reversed hallux?
May just be wishful thinking :)
> > And with very little mental work I can see them
> > transitioning from gliding to powered flying.
> from gliding to flying [...] that transition
> is probably impossible, as flapping destabilizes a
> glider (screws up its angle of attack and all
> that). No living glider flaps.
If flapping only destabilizes a glider, then why do
birds flap, glide for a distance, then flap again?
Wouldn't that cause problems for them? And yet many
birds of prey do this. I think you're mistaking me.
I'm not saying that they merely lifted and dropped
their wings. What I am saying is that they were
putting their wings at an angle and lifting/dropping
them. How could flapping without angling provide any
sort of propulsion or lift? Call it the "undulatory
origin of powered flight" if you will.
> > They would hop from a branch, wings held nearly
> > vertical (parallel with eachother) with respect to
> > the ground.
> Requires dorsally oriented glenoids (or extremely
> flat ones, like in apes) a
> priori. Where do they come from?
An alternative could be that they folded their wings.
> > After a short bout of gliding, they would
> > allow the lift generated to push the wings back to
> > vertical.
> And then they fall again. Counterproductive.
Not counterproductive at all. It generates velocity.
> Where are the non-pygostylians with perching feet? I
> can't see any. Not Archie, not *Microraptor*, not
> *Caudipteryx*. And in chicken embryology the
> big toes migrate downwards and lengthen after having
> started in the classical position seen in
Putting a previously useless digit into a useful
position indicates it was being used for something.
What was it supporting or gripping? I'm not sure, but
I'm willing to venture a guess. Only if the
metatarsals were held flat against a tree trunk or
other surface would the halluces be subjected to
evolutionary pressures. Let's say your FUCHSIA model
is correct for a moment. How would an opposable hallux
evolve and then migrate down to the same plane as the
other phalanges in the foot? Birds simply flew out of
the water, landed on a perch, and by a macromutation
miracle modified this appendage? I'm also interested
in what you think _Rahonavis_ was using its giant
ungual for. Disemboweling fish?
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