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Re: pteros have lift-off

David Peters wrote:

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?

Well, we have a good forelimb for Quetz northropi. But in any case, this goes back to my earlier observation that azhdarchids are disproportionately good launchers among pterosaurs. This likely had something to do with launching away from danger in inland environments. The evolution of the azhdarchoid flight apparatus and launch system is actually quite interesting.

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.

It's actually not a big difference, it just looks that way at first glance. It's the difference of one upstroke, maximum (probably part of an upstroke, since flapping amplitude in pterosaurs seems to be relative small). Even for a large pterosaur, that's a timing difference of a couple tenths of a second or so. Given how much higher they leap using the quad launch, the extra time is more than made up for.

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.

It's big, but not as large as you might think. The wing moves a lot faster than I believe you're giving credit for. Even for a giant, like Quetzalcoatlus northropi, the flapping frequency in cruising bursts was probably just over 1 Hrz, which means that a reduced-span upstroke, under heavy anaerobic power, at max speed, is only a couple tenths of a second. That's slow for a flying vertebrate, of course, but pretty quick overall. Flying animals are fast. Much faster than I think most people realize.

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?

I use the cg, but glenoid works as a marker, too. For a 200kg Quetz northropi launching at 30 degrees from the horizontal, I get a cg elevation (or glenoid elevation) of 3.34 meters from the resting line (i.e. its a somewhat larger number taken from the beginning of the unload). Impressive, but hardly supernatural. And more than enough for clearance on the downstroke.

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

Running speed to break point relationships are rather tricky, actually, but ballpark 6-7 m/s for a big azhdarchid, perhaps, assuming it could even run bipedally at all. Nyctosaurus comes in very wimpy, of course; probably under 4 m/s. But to be honest, I've mostly worried about bipedal leaping ability, because that's much more telling than running speed for several reasons (see below).

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.

I think it's safe to say that pterosaurs were not running off cliffs to launch (not that this is required for albatrosses, either). In any case, in running launchers, the wings are elevated early, but the same basic principle holds as in leaping launch: the wings are elevated by the time the animal leaves the ground for biped launchers. In quad launchers, it happens just after the leap. So there is the difference of a single upstroke in timing.

More to the point, though, running-launch birds takeoff the way they do mostly as an adaptation to water launching. You'll notice that they are almost all semi-aquatic species with webbed feet. They also have short, stout femora, gracile humeri, low pectoral fractions (relatively speaking), hindlimbs shifted posteriorly, and high wing loadings. Only the last one matches with pterosaurs. It is not really a matter of size, nor it is a great way of building up flight speed, per se. Even in the running launch, the last moment is essentially a small leap (though it isn't obvious in most videos).

Besides, we still have the same problem as before: they animal must provide most of the force with the hindlimbs, and most pterosaurs just aren't built for that. Many simply can't do it at all.



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 habib@jhmi.edu