[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



 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