Re: pteros have lift-off

["Jaime A. Headden" <qilongia@yahoo.com>]

Dave Peters wrote:

<Using the same criteria and model, I have a problem seeing Istiodactylus 
leaping. Pectoral girdle smaller than half the size and not fused. Humerii 
huge, okay. Massive antebrachium, okay. Wing finger, nearly three times longer 
relative to torso. Big problem. It has to leap three times higher to follow the 
same wing opening trajectory, whatever the lateral angle, on forelimbs no 
larger than Q. and hindlimbs half the length relative to torso. So comparing 
apples to apples, Istio needs a 3x larger effort on weaker equipment than 
Quetz.>

  I'm only going to posit here (note: I am not inclined to the nuts and bolts 
of physics, so I can't extrapolate actual parameters) that the relative 
required thrust to get a 50kg animal 10 feet up into the air versus a 250kg 
animal 10 feet up will be different. Without assuming the relative masses of 
the animals involved here, the thrust to mass ratio is disproportionately in 
*Istiodactylus*'s favor compared to *Quetzalcoatlus* sp. for the same action. 
As such, Quetz will require more power to launch than will virtually any 
smaller animal.

  Note also here that as Jim and Mike have been saying, the feet are in fact of 
less value in thrusting in quad-launch than are the arms, which provide the 
main arm extension power. I would actually imagine *Istiodactylus*, and other 
long-arm pterosaurs like *Arthurdactylus*, to have a much larger thrust 
capability to their mass on launching than larger pterosaurs, and this may be 
ecologically important.

  I will also note that birds, despite being leg-launchers, possess highly 
mobile shoulder apparati which function to change shape during the wing stroke, 
such that having a unfused scapulocoracoid should not be neccessarily 
restrictive of a quality in quad launching. But then, as I said, I am not 
physically inclined.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)