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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



Now, if bat evolution implied rapid morphological evolution (promisory
monsters) by modification in the development of digits, as apparent
from paper of Sears et al. (2006; PNAS 103: 6581-6586), we may have
here fast-appearence of high-ratio aspects. As pteros have also an
elongate flight digit, that may also apply for them.

Another thing that hypothetical glider ancestors have to change to
become volant may be the position of the hindlimbs, from directing
laterally to direct caudally, because if not, rising the wing would
imply abducting both extremities. There seems to be a more important
aerodynamic reason. For some reason not known by be, the posterior
border of a wing has to be more plexible than the anterior, as this
occurs in birds, pteros, bats, perhaps in insects, where the anterior
border seems to posses more "nervations" (don't know the English
word), or planes, were the trailing edges in wings seem to be hinged
and thus movable.

Question: is the low-aspect ratio of membranes in gliders the reason
for they to fall if flapping? Low-aspect ratio birds flap and manouver
more than high-aspect ratio birds. Thus, can it be that the increase
in aspect ratio has to be not so great in order to achieve flapping
flight from an ancestral glider?


Thus, may, aerodinamically at least, a pterosaur or chiropteran evolve
from a glider which:

a) elongated its digits, what implied a high-ratio wing?
b) Its hindlimbs rotated backwars, as to leave a soft trailing edge of the wing?

I tend to see this as not so improbable, as I do not think ancestral
gliding abilities are severely jeopardized by these changes (after
all, most flyers now can glide if wanting to do so).

However, I accept that only after these morphological innovations can
the glider start to flap.


2008/9/29, evelyn sobielski <koreke77@yahoo.de>:
>
>> And, we might keep in mind that once the wings are large
>> enough to support
>> roughly about 1/4 the weight of the animal at its normal
>> rate of travel
>> (whether achieved by running or leaping), then transient
>> gusts will often
>> provide enough excess lift force to get the animal well
>> clear of the ground.
>> Once that happens, the animal can achieve significant
>> horizontal velocities
>> and cover a respectable distance  on the way back to the
>> ground.  Mobility
>> is greatly enhanced.
>> JimC
>
> Yes, but it still will be WiGging its way along. Actual flight it is as much
> as the Soviet WiG craft were airplanes.
>
>
> Eike
>
>
>
>