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Re: Water-bourne pterosaur launch



There is, as yet, no reasonable mechanism for water launch in pterosaurs published in the literature. However, Jim and I have done preliminary work indicating that a quadrupedal, water-based launch should be possible for many pterosaurs. It is a work in progress, and we hope to have the first good set of calculations in place in time to present the results at a meeting sometime in the 2010 season. Because of this, I prefer not to tip our hand too much. However, a few basic parameters of interest:

- Because water is 800+ times denser than air, pulling oneself out of the water (initial suction effect) takes some work. However, on the upside, pushing yourself along requires very little contact area as the fluid forces are 800+ times greater in the water than air.

- A single leap will not suffice, given the compliance of water. However, a quick series of pushes can do the trick - running launches in birds are more like a series of hops than a typical run (watch the spacing on a high-rate photo of a water-launching bird).

- Birds pull themselves up on the surface of the water by pushing on the air with their wings and pushing on the water with their feet. Pterosaurs appear to manage the same trick, but simply push on the water with both the feet and wings (meaning that the wings need to have only a very, very small contact area, relatively speaking, as they get 800x the force per unit area). As usual, birds get most of the water launch force from the hind limbs, pterosaurs seem to get most of the power from the forelimbs.

Cheers,

--Mike


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181



On Oct 6, 2009, at 4:54 AM, Mark Witton wrote:

Chaps,

Quick question: in numerous threads on pterosaur launch there's been mentions of pterosaurs taking off from water, but, to my knowledge, it's never really been discussed further. The mechanics of water launching have to be quite different to those acting on terrestrially-launching critters, and I've never really been too sure how it would work. Anyone (and I'm particularly glancing over at Mike and Jim here, seeing as they're typically the guys saying it can happen) come up with a suitable mechanism for it?

Back to work.

Mark

--

Dr. Mark Witton

Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk