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Re: Everyone's discussing bird origins...



Jonathan refers to my comment about dynamic instability being a good
way to design in maneuverability:

>         You are absolutely and 100% correct, and I did consider this (I was
> thinking mostly of the X-22 myself, what my father calls the "Shake-apart
> Special").  Do we have _any_ evidence of dynamic instability (I believe that
> this is proper nomenclature) in any animal?

I'd actually argue that *most* animals are dynamically unstable.
Think about what it takes for you to stand up -- it's a *lot* like
what it takes to keep an F-117 in level flight.  When you're "standing
still", you're constantly falling over.  Sensors in your middle ear
detect the motion and cause signals to be sent to your muscles to push
you in the other direction to compensate.  That's exactly what the
flight computers on western fighters do with small movements of their
control surfaces.  Cases of real stability (i.e. body configurations
that don't require sensory feedback to prevent unintended motions --
e.g. falling) are probably pretty rare in animals.  Soaring birds and
cruising fish are about the only examples I can think of.

>   Besides, I can't envision a braking motion which would need to be
> combined with zippy maneuvering.  On the other hand, if a small
> theropod is running, gets unstable, and falls, hey, it's not t-rex!

Here are two experiments you can perform to see these behaviors in
action.  1) chase a bird (especially a bird that lives among humans --
like a rock dove (i.e. "pigeon")) by walking towards it slowly and
only darting towards it when you get really close.  Most birds will
avoid flying if they can, so you can watch how it uses its wings when
it's on the ground.  Contrary to George's claim that chickens are
making "lemonade out of lemons", I think all birds will use their
wings this way if they're not so stressed that they feel they *need* to
fly away.  2) Find yourself a big preying mantis, get it to fly, and
then jingle your car keys loudly.  Mantises are preyed upon by bats.
They have a single ear located on the ventral side of their thorax
right between the two hind legs.  The ear is sensitive to high
frequency sounds (e.g. like those made by a bat).  If you can generate
enough intensity at high frequencies, you can fool the manis into
thinking that there's a bat closing upon it.  One of its most
successful maneuvers under this circumstance is to flare out its wing
covers and curl up its abdomen in order to reduce lift and increase
drag at the same time.  When it does this it either falls like a rock
or spirals off to one side.  In either case, bats will frequently
overfly them and hence miss their meals.  Fighter pilots have been
impressed by these sorts of maneuvers since they do similar things in
a knife fight.

You could probably observe similar braking maneuvers in the way that
fish turn with their fins during a pursuit, but I suspect you'd need a
high speed camera to catch the movements.  In any case, these sorts of
behaviors are definitely out there...

In the same thread, George writes:

] Well, then one could make all sorts of claims about dinosaur
] behavior and argue that, since dinosaurs were so different from
] modern animals, these behaviors are simply not seen any more.

The specific behavior in question *is* seen today.  The discussion
started with LN Jeff talking about how chickens evade pursuers.  The
specific behavior isn't seen in non-dinosaurs.  Analogous behaviors
are seen in other places (e.g. as described above).

] I suppose I do some of this myself when arguing for certain
] plausible behaviors in dino-birds (such as tail-gliding), so perhaps
] I should have extended the same courtesy to you after all.

And perhaps you should try investing less ego in your ideas.  I'm not
wedded to this scenario of how nascent flight feathers might have been
used.  I merely bandy it about because it's plausible and no less
supported than versions that other people throw around with (IMHO)
undue certainty.  That is, it's not *me* that you should be courteous
to just as I'm not being *dis*courteous to *you* when I point out why
I think your ideas don't always merit the certainty with which you
express them.  There are times when I think we could use a little less
personality around here.  If we could all recognize the difference
between attacking ideas and needling people (and similarly the
difference between carefully thinking through ideas and being
"courteous" to the people presenting them) I think we'd be a bit
happier (not that I think we're particularly unhappy here, mind you).

--
Mickey Rowe     (mrowe@indiana.edu)