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Re: Theory on ornithoptering and could Archie do it ?



Archosaur J wrote:

>I'll make this short and sweet. Since Archeopteryx and origins of flight
>aren't >exactly my best studied subjects, I apologize in advance for any
>errors that I >might make.
>
>Okay so one of the big questions circulating through paleontology today
>is: How >powered flight evolved.

One needs to differentiate between flight and *powered* flight, they are
two separate things.  Flight can be seen as simply keeping yourself
airborn, and is surprisingly easy (given the correct power/weight ratio).
Once a certain aerial speed is achieved (approx. 9 m/s) then simple
flapping in enough to maintain flight.
Power flight is an entirely different animal.  Power flight is the ability
to take off from a standing start, to fly at very low speeds and to do
aerial acrobatics.  Power flight is to flight what the 4 minute mile is to
running. Just because you cannot run the mile in 4 minutes does not mean
that you cannot run.  Similarly, just because a bird cannot power fly does
not mean that it cannot fly.
The lack of a sternum in Archae is a bit of a red herring.  It is probable
that the sternum was not ossified, but still allowed muscle attachment.
Also, the new form has a small sternum.

Also it is unlikely that Archae was on the direct line to power flight,
since it lacks a number of critical features such as ligament placement.

>Now as for how powered flight in insects evolved. That's anyone's guess.

Ah this is quite interesting.  For instance did you know that the HOX genes
for wing development are actually expressed in all segments, but is turned
OFF in all but the segment(s) carrying wings?  This suggests that the
ancestral insect actually carried the stuctures which were modified into
wings on all segments. Specimens of fossil insects tend to support this.
It has been suggested that the original structures had another function,
probably temperature control and experiments suggest that the size at which
they become inefficient as temperature controllers (too big) is the size
that makes a difference to falling insects.  Fossil insects show a series
of these stucutures running along the back, but tapering so that the first
is the biggest and the last the smallest.  Switching off the smaller ones
would leave just the larger ones at the front of the body.  Also  . . .er,
but I digress . . .

Chris

cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
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Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.