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