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Re: avian flight



> >That's it. Ebel has addressed this mathematically. First he refutes the
> possibility that *Archaeopteryx* could have parachuted: When assuming
> present air density (small changes there would hardly alter the outcome),
a
> weight of 250 g and a wing area of 479 cm² (too low), Archie's speed of
> descent was 9.13[8233248 in my calculation with the same formula] m/s,
> "corresponding to a free fall from a height of 4.2 m, would hardly be
> acceptable to a bird with delicate bones"<
> SNIP
> >"Even if the rate of descent may be rather low in a good glider, in
> any case the total kinetic energy must be annihilated when arriving on the
> ground or on a branch. An impression of this problem is given by an
> albatross which has to land in calm air, but often tumbles over.<
> But, isn't the albatross "a bird with delicate bones"? No one said that
> Archie would make delivate, graceful landings. Why couldn't
_Archaeopteryx_
> make the same sort of controlled crash on landing?

Albatrosses can probably fly much more slowly -- they can soar, they have an
alula... And recent birds have terribly reinforced pelves fused into one
solid mass with the enormously long sacrum. *Archaeopteryx* has the basal
condition: quite short ilia, 5 (right? or 6?) sacrals, and much less fusion.
BTW, oviraptorosaurs have longer sacra...

> >However, the available mechanisms for speed reduction are restricted,
since
> >the maximum lift coefficient during landing could hardly be greater [what
> >an understatement] than the maximum drag coefficient of cD-max = 1,4 of a
> >cup-shaped parachute.<
> Not quite sure what this means (icky math. I'm working on it though).
> However, why would it be impossible for Archie to rotate it's body (in the
> air) to the verticle, so that the wings and tail are perpendicular to the
> direction of travel (basically stall a moment before landing). I think
some
> modern birds do something similar, when landing on a narrow perch.

For this, one needs to flap very fast (*big* flight muscles), excellent
control, and gimmicks like an alula. When landing on a tree, it is also very
useful to have feet that can grasp a branch; I think Archie would have
slipped in this situation because its halluces were too far up the foot.

> >Here also the not yet evolved wingstroke cannot serve as an escape from
the
> >dilemma [means: Gliding can't be a precursor stage to flapping if gliders
> >already need to flap].<
> This is an assumption. How do we know flapping hadn't already evoloved for
> some other purpose (display?).

Okay: "if gliders already need flapping abilities at the level of modern
birds", see above.

> But, it seems like a common reaction from
> most animals that jump/are dropped from a height (my cat comes to mind,
no,
> I don't throw her off ledges to test this hypothesis). Why would Archie be
> an exception?

Cats flap? All I know falling cats do is they turn themselves around so that
they land legs-first. And cats have legs quite different from Archie's...

> Also, all this talk of landing leaves out how the animal would land in the
> water. I think that an impact with water would cause as much, if not more
> damage to the animal if it wasn't able to slow down. Flying things hitting
> the water, even at a relatively low angle, end up looking bad if they
canoot
> decelerate before impact (Saw video footage of an airplane test ditch in
the
> ocean...).

True. Well, maybe Archie dropped into the water head-first from just above
the sea surface...

> >Furthermore, considerations regarding the origin of flight must take into
> >account that at the beginning of the evolution the wing area must have
been
> >substantially smaller than that of *Archaeopteryx*.<
> True. But this means that there had to be some pressure to enlarge the
> feathers, which I don't think would be present in an aquatic environment
> (see my earlier message on the topic).

Completely true. Therefore, once more, I use HP Thomas Hopp's hypothesis
that wing feathers evolved for brooding. First wings, then flight, not both
at the same time.

> >To be able to fly up a landing site in a curve so that the speed is
> >completely reduced at arrival, as Recent birds can do, requires
completely
> >developed flight abilities. [Coffin for trees-down]<
> I don't see how this is so. This assumes that the animal is flying to the
> tree, and not climbing (If I'm reading this statement correctly).

Yes. See above. I don't think any animal would glide from a tree to the
ground and then climb up the next tree instead of directly gliding there.

> >Yes. *Archaeopteryx* was found in sea sediments.<
> I was under the impression that Solenhofen was a lagoonal, near shore
> environment

True.

> This would mean that...
> >there is no advantage a semi-aquatic insectivore would have over a
> >terrestrial one in there.<

Just that I didn't say that *Archaeopteryx* was insectivorous. I think I
have stated quite clearly that IMHO it was mainly piscivorous. Plenty of
fish of the right size, like *Leptolepides*, were around. (Of course, I
don't say that Archie would have refused to eat one of the 10-cm-long
grasshoppers that have been found there -- if it could catch one.)

BTW: Solnhofen with one e in total.