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Re: Water-bourne pterosaur launch and albatross take-offs
Water-bourne pterosaur launch
or wind assisted?
Given the examples of fledgling albatrossess, which tank often, water
launch doesn't seem to be a problem with a steady breeze and marauding
The presence of webbing on pterosaur toes and fingers are probably
more aerodynamic than hydrodynamic, and help one not to sink into
beach sand too far, but if you've got your flippers on anyway, why not
Getting out of the water in dead calm air, I leave that to Mike and
Jim, but I am reminded of the situation in mayflies, in which wings
get the critter moving pretty fast along the surface, but not
airborne. Pterosaurs, needless to say...
Say... I just Googled "albatross take-off" and went to the videos
category. I was curious if there were any reports of adult albatrosses
take-off from water. Near the top you'll find a funny and instructive
video "Albatross airlines" which makes Mike and Jim's point very well,
that these things have a heck of a time getting airborne on two legs.
Key point made by the video: albatrosses have a terrible time
landing! Something they do, evidently only rarely, such as to lay eggs
and raise chicks. Given the fact that, with the one example we do have
in the ichnite literature, that at least one pterosaur could perform a
perfect two-point landing, then put its other two down for terrestrial
progression, it makes one wonder what the difference is? The
uropatagia would make nice airbrakes. Too much airspeed on landing
seems to be the albatross problem. Not enough airspeed to gain flight
seems to be their problem on take-off using their feet and wings. So
maybe the albatross model is not so good for pterosaurs. Some
pterosaurs apparently were able to come to a complete stall-stop
before touching down. Does that fact give us any clue to their wing-
flapping take-off abilities?
Another Google video "Tiger Shark vs. Albatross" reports that 10% of
fledglings become shark bait and a very few get a symbiotic aerial
assist (or motivation) from sharks (SATO? [shark-assisted take-off])
attempting to bite them.
Yet another video "Albatross takes flight" shows us one on a rocky
outgroup, too rocky for a run, so it elevates its wings, pushes off
once with its legs, flaps, rises and soars on incoming breezes. This
video makes a major point. If pterosaurs were going to land on a flat
surface, they, like the albatross, probably knew when and where
breezes were available for wind-assisted take-off and predators were
not likely to be present. Those that failed became extinct. 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
The problem with the manus tracks is more complicated.
One side says fingers 1-3 faced palms anterior in flight and 4
hyperextended to fold (Bennett 2008). That means the former
connection between the lateral surface of metacarpal III and the
medial surface of IV have broken because the now ventral surface of
III is close to the now ventral surface of IV rather than sitting on
top of IV as expected in a supinated manus. In ichnites that
hypothesis puts mc IV impressions medial to impressions of I-III.
Adherents see this impression in ichnites. It also forces some unusual
configurations of the antebrachium and humerus to get the fingers to
line up to match ichnites.
Side two says fingers 1-3 had palms palmar in flight and 4 was twisted
to flex and fold posteriorly (Peters 2001). That means the connection
between mcIII and McIV remains as in all tetrapods -- if the cell
layer between them moved "flounder like" from the medial surface of mc
IV to the dorsum now rotated to the anterior, but not far because the
plane of I-III is ventral to the extensor tendon process. That
hypothesis extends fingers laterally during terrestrial excursions to
match tracks with elbows slightly out, slightly back and the
antebrachium not suppinated. That hypothesis places mc IV posterior to
the root of finger III impressions, but only finger III impressions
are known. In this hypothesis mc IV does not make an impression.
Finger III supports it. (new contact point for the recoil mechanism?)
Side two also places the center of balance in pterosaurs at the
glenoid and over the toes. 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.