Re: pteros have lift-off

[David Peters <davidpeters@att.net>]

Earlier I asked Mike Habib about pterosaur ancestry. Whether archosaur or 
fenestrasaur, in either case the forelimbs were relatively small (witness 
Cosesaurus, Longisquama, & Sharovipteryx on one hand, Euparkeria and 
Scleromochlus on the the other). The pelvic muscles and hind limb were further 
developed with anterior processes of the ilium and prepubes to add anchors for 
additional muscles, in the case of fenestrasaurs, pelvic development and leg 
elongation coincided with the decoupling of the caudofemoral complex and the 
attainment of bipedalism. In the case of archosaurs, it coincided with leg 
elongation and the attainment of bipedalism without decoupling the 
caudofemorals. So in outgroups to pteros, we've got bipedalism, small forelimbs 
long hind limbs and big hips. If pterosaurs are going to quad launch, they 
can't inherit it from these guys.

And they don't. All on their own pteros develop elongated antebrachia. So much 
so that they can reach the ground while bipedal, leading to all the present 
arguments about bipedalism vs. quadrupedalism. Putting aside Bennett's and von 
Huene's leaping hypotheses (with Z-fold hind limbs), pterosaurs were also 
clinging to trees, pretty much like lemurs and tarsiers and maybe 
Archaeopteryx, if Archae used its wing claws to grapple. Grappling trees 
permitted full deployment of the wing while grappling because they grappled at 
a tangent to the tree diameter, etc. So flying out of trees, no problem. They 
fell or leaped clear of the tree trunk, twisted belly down and started 
flapping. Right?

Now, if grounded, what to do?

Mike habib wrote:

<<Are you using the term power in its technical sense, or in a general "where 
does the speed come from" manner?>>

I'm wondering where does the ability to leap several torso lengths above the 
ground come from? I have little problem with Quetz. Huge pectoral girdle. Huge 
humeri. Massive antebrachium. Presumeably a large radius of movement and store 
energy at the metacarpus. Wing finger, I presume adds nothing to the leap, but 
it was relatively short with a small opening radius. Other fingers leave the 
earth in a I-II-III fashion according to length. Agreed?

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.

MH <<I am curious as to what
> you plan to measure from the diagrams - aside from showing the proposed
> kinematic, most of the relevant numbers (structural strength, power output, 
> etc) won't be measurable from an image.  Are you just  referring to wing 
> clearance?>>

Wing clearance is key. You can't open the wings, if quad, until the distal 
metacarpals leave the ground by leaping. Then they have to leave the ground a 
distance and angle sufficient to open fully before the leap comes to a crashing 
finish. That means the minimum distance of a leap is easily measured. Is it 
enough in a worse-case scenario, like Istiodactylus?

I'm curious as to what you and Jim say about wing clearance when bipedal. Seems 
to me to be no problem if a pterosaur deploys its wings while standing on two 
legs, then either leaping with hind limbs, like a bird, or running to take-off 
speed, like other birds.

There's also the case of Rhaeticodactylus in which the forelimbs were no more 
robust than the hind limbs and the humerus was unusually elongated. Was it 
different, as a leaper, or the same?

Finally, if there was a change from leaping with the hind limbs to leaping with 
the forelimbs, this should be visible in the anatomy and phylogeny of the 
Pterosauria. Since outgroups had to be hindlimb leapers, which anatomical 
marker tells us that the forelimbs have taken over? And which is the first 
taxon to have this character?

David