Re: Water-bourne pterosaur launch and albatross take-offs

[David Peters <davidrpeters@charter.net>]

 Water-bourne pterosaur launch

Dead calm?
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  
sharks.

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  
use them?

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  
seen.

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.

David Peters
St. Louis