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RE: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
I know early flapping flight would shorten the distance of a glide, but what
if that was the whole point intitially? What if the ealiest stage of flapping
was simply to slow down and break before landing? I started wondering about
this while watching videos of birds landing; here is an example.
http://www.youtube.com/watch?v=cilkYHn0BPQ and here
The main problem I'm still having with the cursorial model is one of
energy spent vs energy taken in from the prey. Now before you role your eyes
and say, "not this again" consider that a protobird leaping up into the air and
using its primtive wings (which lack aerodynamic flight feathers) would have to
flap its "wings" very rapidly to produce any kind of thrust. These rapid flaps
would have been anaerobic in nature, which means they would consume large
amounts of energy in a very short amount of time. Now if these protorbirds were
leaping up to catch insects, I doubt the amount calories they gained vs the
amount burned would have been very beneficial; even if it were, I imagine there
would have been more effective and less energy consuming ways of increasing the
height of a jump. Most (if not all) of the worlds most specialized leapers have
greatly reduced forelimbs and greatly enlarged hind limbs: examples include
grasshoppers, frogs, crickets, kangaroos and rodents. The
benefit for this is obvious: by reducing the weight of the forelimbs, while
shifting more weight to the hindlimbs, a jumping animal would reduce the load
on its hind legs. This would be more effective than inceasing the size of the
arms and using primitive feathers for lift, since all the power from the leap
would come from a single muscular contraction of the enlarged hindlimbs and
would not involve a series of rapid energy consuming flaps of the arms.
Assuming a protobird could get past all these problems, and achieve some form
of short distance flight, it trying to use this to catch an insect would be (as
GSP put it) like, "trying to shoot down spitfires with a 1908 wright flyer".
Flying insects are not slow, and animals like bats and fast flying
insectovorous birds have to be quite agile to make a living eating them.
> Date: Mon, 29 Sep 2008 20:06:03 -0300
> From: email@example.com
> Subject: Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
> To: firstname.lastname@example.org
> CC: email@example.com
> 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-hind limbs 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 hind limbs 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
> 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 <firstname.lastname@example.org>:
> >> 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