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