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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.
Assistant Professor of Biology
Woodland Road, Pittsburgh PA 15232
Buhl Hall, Room 226A
On Oct 6, 2009, at 4:54 AM, Mark Witton wrote:
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.
Dr. Mark Witton
Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Tel: (44)2392 842418