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Re: pterosaur take-off analog
On Oct 5, 2009, at 11:07 AM, David Peters wrote:
1. Knowing when and where to land
2. Knowing to land in trees tops when the ground was "busy"
3. Knowing to land on deserted islands or flotsam when trees weren't
4. Knowing when the breezy parts of the day occurred to land and
5. Landing somewhere with a ten-foot drop off nearby (probably a
6. Climbing up a nearby tree or vertical surface to launch (not
exactly like WAIR, but maybe)
7. Or simply launching in some sort of springy fashion if all else
It is quite reasonable to presume that numbers 1-6 would be used, as
appropriate, by various species. However, all living powered flyers
are capable of number 7, as well, and what is more, their primary
launch mode is generally some version thereof. In other words, living
birds and bats have structural adaptations to launch is your "some
sort of springy fashion", and this appears to be the mode that drives
their launch-related morphological evolution. Assuming that the same
is true for pterosaurs, their morphology should reflect their primary
launch mode, which would be the one used without special conditions.
Wind and elevation then helps from there.
While the recent animation on pterosaur arm launches is an
interesting look at engineering and dynamics, it depends on a worst-
case scenario of a flat surface and no breeze.
Of course; it does little good to layer on special conditions and then
presume that the result is a typical launch that properly reflects the
adaptations of the animals in question.
Given any other scenario, other solutions may be more tenable given
the lesson of the fledglings.
I'm a bit intrigued by your use of "tenable" here. What I think you
are saying is that other launch solutions may be vaguely plausible,
given special conditions, and presuming that such conditions were
always available. That's not the same as being "more tenable".
Consider: the quad launch model matches with the known quad stance
(trackway evidence), matches the structural evidence (strength of
bones in bending), explains the size differential between the largest
pterosaurs and all other flying animals, and explains the observed
patterns of maximum size within Pterosauria. Biped launch models fail
on all these accounts, and furthermore have the issue of trailing edge
flutter and angle of attack. In fact, right off the starting line,
the quad launch model is the more parsimonious, as it entails a quad-
walking animal also quad launching. A biped model presumes a shift in
gait (at a mechanical disadvantage, no less) from quad to biped. So
really, all I, Jim, and others have done is gather some quantitative
evidence to support what should be the null model. No evidence has
yet been accrued to refute the null hypothesis and/or support an
There's still the problem of no clear metacarpal IV impressions,
only digits I-III. So there may not be a lock and recoil mechanism.
Well, I think there is a huge MCIV impression, namely the middle of
almost every manus track. Several track workers have agreed with me
here. However, let's presume that the tracks really are just 1-3
(which would be odd for a number of reasons, more on that some other
time); as long as MCIV can be pressed against the substrate during
preload, the lock and release would work. Going even further, and
presuming that for some reason MCIV just cannot touch the substrate,
and that things like Quetz somehow levitate to support themselves on
digits 1-3, the lock and release is not required for launch: it just
makes it faster. In fact, the low-power version of the launch I
calculated used only counter-motion preload (and not even much of
that); it had no elastic storage at all.
And the problem of what to do with that giant wing finger rotating
straight down at the moment of launch is still vexing.
If it did so, then it might be vexing. We've discussed this
previously: the wing finger does not rotate straight down; it stays
mostly closed until the first upstroke (it opens about 10 degrees
during the catch and release trigger). Note, for example, that we did
check for clearance with the ground in the digital model, and the
animation used published joint limits, so we did not have to do
anything fancy for clearance (clearance is improved by quad launching,
of course, because there is more height gain during the leap).
Assistant Professor of Biology
Woodland Road, Pittsburgh PA 15232
Buhl Hall, Room 226A