[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Water-bourne pterosaur launch and albatross take-offs
David Peters wrote:
Water-bourne pterosaur launch
or wind assisted?
Dead calm works, gusts help.
The presence of wind creating lift on Albatross wings demonstrates
that less stress was on the hind limbs, but I'm sure Jim and Mike's
figures already cover that.
Albatrosses cannot land in trees, evidently, or trees are not
present on the islands they frequent, but trees were available for
pterosaurs of all sizes. Grappling claws on wings (palms facing
medially!) testify to their arboreal abilities. So dropping and
flapping could have been the most common method of take-off. Walking
to a nearby tree and climbing it could have the same ultimate
effect. But removing all wind, trees, elevations and foresight,
perhaps the leaping model was employed, as the figures indicate.
Some sort of tracks will show this someday. Whether those last
traces will be feet or hands remains to be seen.
Even if the palms did face in a manner consistent with climbing
ability, this does not make all pterosaurs arboreal, or even able to
climb. Some species probably were arboreal, but animals like
azhdarchids and ornithocheirids do not display a morphology, or size,
consistent with arboreal living. Also, arboreal birds do not simply
drop to launch, in most cases. Gravity helps, but they still leap.
Bats drop, but they're inverted. Even with wind, trees, elevation,
and foresight, living flapping flyers push from the substrate to
launch. They can push less if there is assistance from wind and/or
elevated positions; they push the hardest in calms on flat surfaces -
but they still push off the substrate. Keep in mind that even animals
like hummingbirds get most of the launch force from leaping (59%,
according to Tobalske et al., 2004). Therefore, leaping to launch is
not a "last ditch" effort - it is the typical manner of animal
takeoff, modified in the prerequisite force according to transient
conditions. Jim already covered the issues with dropping giant
pterosaurs for takeoff. Unless you have branchless Sequoias around,
you get a really need lawn dart.
So any excess depression of manus prints vs. pedal prints is due to
their much smaller surface area, not their weight distribution.
They're more like canes.
Comparing areas, the manus prints are indeed smaller in their contact
area, but likely not by a margin consistent with the above hypothesis,
which would leave very little body weight on the forelimbs. But, that
aside, if this stance is correct, the the hind limbs take most of the
walking and running forces, and so I would expect their strength to
scale with positive allometry, as in birds. The hind limb strength
in pterosaurs does not scale allometrically, however, it is
essentially isometric. In birds, the femoral strength scales with
substantial positive allometry, according to body size (exponent of
about 0.88 versus the isometric 0.67).