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more bird origins
I haven't been around to follow up on the last few posts on this topic, and
now that I've had time to catch up on the commentaries that have been posted,
I hope this isn't too stale. If it is, I guess Mickey will kill it for the
list. [ Nobody's complained about the thread yet. -- MR ]
With respect to your suggestion that "The verticle attack theory
incorporates the sicle claw more fully...", I agree; it certainly doesn't
make much sense for the development of such a weapon "...to kill bugs", as
you put it.
Ronald Orenstein comments that his original suggestion had to do with
arboreal creatures leaping upward to pursue prey, and developing wings as a
result of this action, as opposed to verticle attack. I had missed or
forgotten this original comment, and was thinking purely of the development
of wings as the result of the downward pounce, and the subsequent awkwardness
of dealing with the prey when wings haven't yet developed. Coupled with
Ronald's concept, I see more demand for the environmental adaptation of
wings. I don't see the two concepts as mutually exclusive at all.
The problem I see with wing development from the verticle attack mode alone
is that, as a means of fall control, arms aren't very effective in short
distances, either for braking or for stability. Having spent a great deal of
time in freefall, I am familiar with the time it takes to gain stability
using body position (including arms), and unless our developing friend is
jumping from quite a height above his prey, he won't have it. And without
full braking ability, the adequate height requirement for manouvering will
prove a significant problem upon landing. Or, more accurately, splattering.
Now, if we presume the existence of some airfoil attributes on our friend's
arms to begin with, I concede the point. Nick Longrich suggested that part
of a wing may be of no use, but I'm not sure of that. It sort of depends on
the rate of development of flying traits. It certainly seems that for the
pouncing scenario, partial development would help. A real-life example in
support of this is the problem of a partial canopy deployment. In the event
a skydiver finds his canopy has deployed, but is in some way partially
deflated (as in the Mae West or Bow-tie configuration), he must judge the
pros and cons of cutting away and deploying backup. Proximity to the ground
and the extent to which the partial deployment is braking his fall are the
primary considerations. Automatic Activation Devices are designed which will
deploy the backup automatically if fall rate is too great. But often the
partial deployment is adequate; and in the sense that a developing
"protobird" would use partial wings to brake and angle attack, a partial wing
would provide similar assistance. Evolution from here to full wings is easy
to imagine... even for me!
Incidentally, my skydiving experience also leaves me with an understanding of
the difficulty in accepting gliding as the precursor to powered flight. Once
one is gliding (which is what freefall is), the type of flapping motion
required for powered flight is a sure way of destroying all stability.
Similarly, once under canopy, you are gliding again, and a braking motion is
utilized to provide a soft landing. Near the ground, alternative canopy
manouvers are dangerous, again, because of the sudden instability. Which may
explain why the flight-from-gliding pathway is travelled so infrequently, as
suggested by Stan Friesen.
Now, this brings me (upon pushing real hard on my imagination) to some
comments which were made regarding stability. You commented on sailing, and
I got to thinking about fish, and the similarities between swimming and
flying; since then, some discussions have addressed the development of flying
fish. Tell me, is there any reason fish couldn't have developed into birds?
Nathan Myhrvold's comments intrigue me. After all, if land forms could
evolve from the ocean, why did flying forms have to wait for land forms
Just a thought.
Oh... by the way. I wouldn't have argued that gliders did not become fliers
because those niches were taken. Not because two of three flier radiations
took place while there was already a flapping flier (an excellent point), but
because there's almost always a new angle on exploiting an old niche... which
is probably why two of three flier radiations took place while there was
already a flapping flier... :-)
Wayne A. Bottlick