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Re: pteros have lift-off

Mike Habib wrote:

This has already been addressed, but the basic error here is that you are making the wing finger open far to early. Quetz requires that robust equipment because it is so large.

Not so. I'm working with the small Quetz. Torso same size as Istiodactylus. Smaller Zhejiangopterus had an even smaller overall size. Same overall proportions as the mid-sized Quetz. Not sure we have any complete giant pterosaurs. All such reconstructions are scaled-up versions of the man-sized ones and smaller, are they not?

Istiodactylus does not have nearly so much mass to accelerate. More importantly, the launch is essentially a "leap first, flap second" situation - which is true of most avian launches, too (it just looks simultaneous to us, because they're quick). Technically, the wing finger opens on the way into the first upstroke (after it has been raised a fair bit), but the basic idea is that the leap precedes the upstroke.

Mike, everyone knows in birds they start in the folded position, basically laterally. Out and up or up and out. In your scenario, pteros start with the folded position, basically ventrally and on the ground. BIG difference.

So, the summary comparison for quad versus biped launching, with regards to timing and clearance is that quad launching adds an upstroke period after the leap (while bipeds can upstroke a bit earlier), but purchases much greater launching power for this price. The question then becomes rather straight-forward: does the extra power give enough height and speed to offset the slight cost of the extra upstroke time? For all pterosaurs I have yet tested, the answer is yes. I believe this is true for Jim's work, as well. This becomes especially true when one considers the lack of power in the hindlimbs of many pterosaurs (big hips or not, they couldn't be generating more force than the femur could handle).

So pteros go from a complete down position at the moment of becoming airborne to an up wing position prior to apogee? That's one heckuva leap. Do you start at the zero point measuring acetabulum or glenoid height? And how many of these height units does your favorite pterosaur have to achieve in the first leap?

How fast do your calculations say a few particular pteros can run before they get to the femur breaking point?

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.

It's simply a matter of the fact that bipeds don't leap as high. The ability to hold the wings out while standing looks like it gives better clearance, but it doesn't actually do so. The first flap occurs near the top of the leap, in both biped launchers and quad launchers, so the clearance is set by the height of the leap. More leaping power means more clearance. Again, it's very important to remember that even birds leap BEFORE they deploy the first downstroke. The only thing they get to do earlier than a quad launcher is the initial upstroke, and the expected upstroke time can be calculated alongside the estimated leaping height, so the hypothesis of clearance advantage is testable. This isn't to say that biped launching never has advantages - burst launching birds can take off at extremely steep angles, which the vast majority of pterosaurs probably couldn't manage (possible exceptions being very tiny things, like anurognathids).

Googling "Albatross take-off" and "Swan take-off" both seem to show the wings being held high, never dipping below the midline of the bird, sort of an upper half-only flight stroke. Valid or no? I don't see any real leap here except that the albatross runs off the cliff, falling to gain speed then it's flying. Important observation here? I see an analogy in pteros, depending on species.

Other markers include bracing in the forelimb for compressive loads (seen in relative joint areas, synovial sac attachments, dp crest orientation, and trabecular strut orientation within the dp crest).

Since the dp-crest varies so much in pterosaurs, does this tell us anything about their launch mode? Does a warped or a hatchet-shaped deltopectoral crest change things?

Have you compared "upper deckers" (short scapulae/long coracoids) with "bottom deckers" long scapulae/short coracoids)?

Still learning how this works.




Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181

David Peters davidpeters@att.net