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Re: Floating pterosaurs

Comments inserted.

----- Original Message ----- From: "David Peters" <davidrpeters@charter.net>
To: "jim cunningham" <jrccea@bellsouth.net>; "Mike Habib" <mhabib5@jhmi.edu>
Cc: <dannj@alphalink.com.au>; <tommy.tyrberg@norrkoping.mail.telia.com>
Sent: Tuesday, July 07, 2009 5:07 AM
Subject: re: Floating pterosaurs

Shoulder-deep and deeper water, the pterosaur had better  float. Right?


Scenarios for deep water take-off. M. Habib wrote: "That would presume that pterosaurs used an avian-style launch, which is doubtful. Granted, I'm a little biased on this issue, having published a paper on it, but Jim and I also have a rather substantial amount of data to back it up. So, while I agree that a larger pterosaur would have trouble launching from the water in the manner of a large living seabird, I also suggest that they did not have to, using alternative modes of launch, instead."

The alternative modes Mike refers to, I presume, is launch from land or tree in the forelimb leap manner he proposed recently.

No. Mike and I agree on launch mode (which is still largely powered by the forelimbs), and are currently working together on technique and power production for deep-water launch. So far, it is looking quite feasible.

If so, that mode obviously would not work for pterosaurs as the aqueous substrate tends to buckle.

One takes that into account of course (though it isn't a buckling).

Given a floating/resting configuration with wings folded and hindlimbs laterally floating, just unfolding some big wings underwater seems problematic.

I can't think of any launch related reason why a pterosaur would want to unfold them underwater into full span configuration.

There is nothing to prevent a pterosaur from extending its wings slowly under water and raising them to the surface so that it assumes a flying configuration while floating.

There isn't. However, there is also no reason in calm water and no-wind condtions why they would want to do so.

My imagination falters at this point (with a brief leap to a vision of Jesus-lizards running on the water surface),

That's the wrong scenario. Like land launch, no running is required. You seem to be anticipating that the animal is going to flap itself out of the water while running like a swan. That is neither likely nor a productive technique for a pterosaur. When thinking pterosaur launch, don't think avian. They wasn't birds.

but now we get to the issue of upper and lower decker pterosaurs. Depending on relative length in the coracoid and scapula, the wing root is located high or low on the torso -- under or above the water line in a floating pterosaur.

The difference in shoulder positioning between the upper and lower-decker pterosaurs isn't really all that great on the grand scale. The lower positioning does allow a more powerful upstroke without hurting downstroke power due to the muscular realignments. In fact, taken together with deltopectoral crest realignment and coracoid flange reshaping, it allows the power of both the up and downstroke to be enhanced.

Can you get those wings above the water and flap them only in the upper half of the flap cycle?

You could, but again -- in calm water and no-wind condtions I can't think of any reason you'd want to.

If so, can you get sufficient power for take-off with the added drag of the water? Do the feet help?

Dave, you're visualizing the wrong launch technique. Keep in mind that for the appropriate launch technique, added water drag is an asset rather than a hindrance ( I love fluid mechanics). That said, neither Mike nor I are likely to say too much about the technique in detail till our paper is ready :-)

Better look for some flotsam.

As an aside, I strongly suspect that KJ1 and KJ2 arrived above their final resting places as flotsam..... :-)

BTW, there are techniques by which the uropatagium can be used to provide substantial thrust while swimming (far more than the pes). I've not yet investigated whether they are likely to have been so used to any great extent.