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Re: pteros have lift-off
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
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
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?