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Re: FOUR, THREE, TWO, ONE . . . PTEROSAURS HAVE LIFT OFF!
Congrats again to Mike Habib on the publication of his paper on quad
lift-off. -- AND on all that great publicity! It's all over Google.
While Mike makes a good case, I was still a little disappointed not
to see a step-by-step sequence illustrating this launch sequence in a
variety of pterosaurs. In the spirit of 'spirited discussion' I'd
like to challenge Mike a little, again.
Quad launch from a tree was, no doubt, customary among pterosaurs
clinging to tree trunks like lemurs do. If perching on branches
bipedally, a simple drop and fly seems appropriate.
A terrestrial quad launch begins with all four limbs on the ground,
the wing finger vertical, I presume. A crouch, or a run and crouch,
followed by a fantastic leap powered by the forelimbs would be the
first few sequence actions in a quad launch, I presume.
At manus lift off, the metacarpus would, of necessity, still be
vertical, having just pushed off the earth like a airborne pole
vault. A vertical metacarpus means the wing finger was still in the
vertical plane, but no doubt beginning its rotation snap to the
flight position. The question is: how long does this take? After
passing the horizon, the wing finger would be on a collision course
with the earth--unless the proximal wing had rotated laterally
sufficiently to enable passage of the entire wing above the
substrate. The clearance shrinks with every passing nanosecond.
Do certain pterosaurs have to jump higher because they have longer
wings that need to clear the ground and produce lift before the
apogee of their initial leap? It seems so.
The quad launch of Quetzalcoatlus, with a robust scapulocoracoid,
tucked wing fingers no higher than its notarium and strong, stork-
like legs, creates one scenario that is more feasible than what follows.
The quad launch of Istiodatylus, with a much smaller scapulocoracoid,
tucked wing fingers several times longer and relatively weak legs
several times shorter presents quite another scenario. Istiodactylus
would have had to leap several times higher, relative to its torso,
than Quetz would have on ostensibly weaker landing/launching gear.
Certainly in both cases, immediately after the forelimbs have
recoiled from their airborne vertical extension following the leap,
the wings would have risen laterally as the wing fingers extended in
preparation for that first down flap. I'd just like to see this in a
set of illustrations hypothetically taking pictures every tenth of a
second in a worse case scenario. Somehow the wingtips have to clear
the substrate just in time.
Jim Cunningham mentioned something about this:
"John Conway and I also did a time-stepping illustration of a Quetz
doing a terrestrial quad launch on a poster that we presented at
ICVM-7 in Boca Raton, FL"
Sure wish I was at that conference.
There is some evidence (which I have not seen) for a bipedal launch
in the literature. Unfortunately I don't find it in Mike's reference
A New Pterosaur Tracksite from the Jurassic Summerville Formation,
Near Ferron, Utah
Authors: Debra Mickelson1; Martin Lockley2; John Bishop3; James
Ichnos, Volume 11, Numbers 1-2, Numbers 1-2/January-June 2004 , pp.
Pterosaur tracks (cf.Pteraichnus) from the Summerville Formation of
the Ferron area of central Utah add to the growing record
ofPteraichnustracksites in the Late Jurassic Summerville Formation
and time-equivalent, or near time-equivalent, deposits. The site is
typical in revealing high pterosaur track densities, but low
ichnodiversity suggesting congregations or“flocks”of many
individuals. Footprint length varies from 2.0 to 7.0 cms. The ratio
of well-preserved pes:manus tracks is about 1:3.4. This reflects a
bias in favor of preservation of manus tracks due to the greater
weight-bearing role of the front limbs, as noted in other pterosaur
track assemblages. The sample also reveals a number of well-preserved
trackways including one suggestive of pes-only progression that might
be associated with take off or landing, and another that shows
pronounced lengthening of stride indicating acceleration.