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Re: Velociraptor profiles and a little background



A late answer...

----- Original Message -----
From: "Waylon Rowley" <whte_rbt_obj@yahoo.com>
Sent: Thursday, March 21, 2002 4:03 AM


> David Marjanovic wrote:
>
> > I think these are 2 examples of how a sophisticated
> > control of wing positions might arise... but not
> > flapping. To get slower by flapping, BTW, requires
> > (I assume) pretty sophisticated flapping and not
> > just any sort of waving one's wings around.
>
> Maybe instead they were performing a series of short
> dives during gliding. They would fall a short
> distance, angle their wings so that they moved up, and
> then repeat that process (somewhat "stalling" in
> mid-air). So the angle of the leading edge of each
> wing is pointing anterodorsal, then switched back to
> horizontal or anteroventral (relative to the axial
> column). I can imagine a figure-8  flight stroke
> evolving from something like this.

I can't... it's too slow, it's gliding with intercalated parachuting, sort
of. Interesting idea, though.

> Hard to say *why*
> they would do this. It may have given them more time
> to "zero-in" on their target, or kept them from
> reaching the ground at a more than safe speed.

It may also have given the target quite a lot more time to escape...

> I'm not sure if you're playing
> devil's advocate, or if you have a different
> viewpoint.

When I'm playing devil's advocate I am and sound sarcastic. :-)

> If the latter is the case I would be
> interested in knowing how you believe flight evolved.

Okay. Key ref: Ebel 1996. Modified, though: You already start out with a
fully feathered and winged coelurosaur that decides to go fishing. For that
it's pretty useful if it can swim. How would an animal of this shape swim?
It can't wriggle its stiff, thin tail. It doesn't have webbed feet, so using
the long, thin legs isn't efficient either. But if tries to grasp a fish
underwater, it gets forward -- it is developing underwater flight. It
doesn't specialize in this, it breeds on dry land (shading as always its
large clutch with its long, broad wings, unlike a penguin) and searches a
considerable part of its food there. You get something like a dipper, sort
of; *Archaeopteryx* is IMHO an example of such an animal. (Difference:
Dippers can already fly.) How does such an animal get quickly out of the
water when it needs to? By jumping out like a penguin -- by simply swimming
upwards into the air. When beaten fast enough, the wings can, if they are
large enough, carry the animal on (if it is small enough, but
*Archaeopteryx* certainly was, and so was the even smaller *Microraptor*, so
a theropod in this size range is to be expected). Advantages that lead to
the retention of this ability, rather than it being selected away for being
too expensive? The ability to flee; today birds have double the life
expectancy of mammals of the same size. Allows one to hunt much closer to
the crocs :-) . The ability to rise high above the water and look for fish
from above -- much more efficient than looking around in the murky depths
themselves. And maybe the ability to show off -- sexual selection strikes
again.
        "Advantages" when tested against to the fossil record: It can happen
fast, I think (neat explanation for the lack of fossils). It can probably
happen in e. g. mountain rivers (where today's dippers live) (another neat
explanation for the lack of fossils). It can explain what the hell Archie
was doing all day, and it can explain why the basal, erm, hm,
maniraptoriforms look more like Archie than the derived ones, respectively
why they all look so secondarily flightless to some. And it explains why
nonavian theropods (except the aye-aye-analog... which may be very close to
birds...) seem so ill-suited to climbing (can't even sprawl their legs),
including the fact that during chicken ontogeny the first toes start high up
and short and later migrate to the level of the others. IMNSHO flight came
first, arboreality second.
        In short, hard positive evidence is totally lacking, but I do think
it is much more plausible than all alternatives I've seen so far, including
all versions of the arboreal _and_ the cursorial hypotheses (and >gargl< the
attempts at a compromise between those two). (Keep in mind that I haven't
seen the stuff about vertical running yet... <meditating> W4tP... W4tP...
W4tP...)