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




----- Original Message ----- From: "David Peters" <davidrpeters@charter.net> To: "dinosaur mailing list" <dinosaur@usc.edu>; "jim cunningham" <jrccea@bellsouth.net>; "Mike Habib" <mhabib5@jhmi.edu>; "Mark Witton" <Mark.Witton@port.ac.uk>
Sent: Wednesday, October 07, 2009 6:50 AM
Subject: Re: Water-bourne pterosaur launch and albatross take-offs


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 difference is in the effectiveness of their use of full alternating momentum reversal during the final stages of the approach to touchdown.

The  uropatagia would make nice airbrakes.

But are on the wrong end of the animal for appropriate control of the pitching moment while doing so. Don't get me wrong; they do serve that purpose to a consderable extent, combined with appropriate average placement of the wings and orientation of wing thrust relative to the cg -- so that the wings are doing more of that job than the uropatagia are. But by the time of the touchdown itself, the uropatagium is unloaded so that the legs are unimpeded in their fore and aft movement.

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.

That's right.

Some pterosaurs apparently were able to come to a complete stall-stop before touching down.

As can some birds, using full alternating momentum reversal. I wouldn't call it a stall though, since they are not stalled, albeit that they are going more slowly than steady-state stall speed.

Does that fact give us any clue to their wing- flapping take-off abilities?

No. Full alternating momentum reversal doesn't provide enough thrust for liftoff. Just enough for settling in.

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.

No doubt they did.

Those that failed became extinct.

That's wrong. They didn't need the winds or the elevation to takeoff, and even from a flat surface in a dead calm, the larger pterosaurs were already moving faster when their hands left the ground than their predators were able to run. About the only way for a land predator to capture a pterosaur would be an ambush from the front quarter, or an ambush from any direction when the direction ahead of the pterosaur was obstructed. My hunch is that pterosaurs on the ground tended to orient themselves with open areas ahead of them. I've been thinking about doing a sketch of a rear quarter view of a pterosaur in the midst of a turning takeoff (one hand still on the ground. but both legs clear and already in turning flight position) while in an effort to escape an on-rushing predator coming in from the front quarter.

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.

I'm having some trouble imagining a Hatz, Qn, or Aramb perched in a tree. Sure would be a big tree, and why bother when you're pretty much predator proof anytime you're in a reasonably open area?

Grappling claws on wings (palms facing medially!) testify to their arboreal abilities.

Do me a favor and sketch me a Hatz climbing up into the upper branches of a tree.... :-) Since the uppermost branches are likely to be unable to support the 1200-1500 pound loads that the pterosaur would impart to them during the launch process, the big pterosaur would also need to find a tree tall enough that he could gently hop or drop out, gain flying speed from the fall due to gravitational acceleration, then pull out of the high speed dive before impacting the ground. How tall a tree would that take? Hint: I already know the answer to that, and it's an impressive tree.

So dropping and flapping could have been the most common method of take-off.

OK, a pterosaur messing about on a beach sees a predator approaching. So being unable to run rapidly, he then procedes to walk or canter to the nearest tree (somewhat rare on beaches) while the predator is running madly toward him. Upon reaching the tree, he tries to clamber up it in time to evade the onrushing predator. Umh, tasty pterosaur. Why didn't he just launch from where he was when he first noticed the predator approaching? Within his own body length, he would be in the air and moving faster than the predator could, and would be increasing the distance between them rather than decreasing it.

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.

:-) If its the pes, then you've found a previously unknown pterosaur with a totally new morphology.

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

No, it just means that IV is now humongously bigger than III.

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.

Thereby placing them in a terrestrial posture which makes a rapid takeoff impossible. Sounds to me like Darwinian processes would do away with that pretty quick. Tasty pterosaur. JimC