Re: FOUR, THREE, TWO, ONE . . . PTEROSAURS HAVE LIFT OFF!

[David Peters <davidpeters@att.net>]

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  
list.


A New Pterosaur Tracksite from the Jurassic Summerville Formation,  
Near Ferron, Utah

Authors: Debra Mickelson1; Martin Lockley2; John Bishop3; James  
Kirkland4

Ichnos, Volume 11, Numbers 1-2, Numbers 1-2/January-June 2004 , pp.  
125-142(18)

Abstract:
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.

David Peters
davidpeters@att.net