Re: Water-bourne pterosaur launch

[Mike Habib <habib@jhmi.edu>]

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