RE: Biomechanics

[John Clavin <jclavin@microsoft.com>]

>First, what figure would you put on the pressure at the level of the lungs
of a
>large, submerged, snorkelling _Brachiosaurus_ individual with the lungs
about 20
>feet (a tad over 6 meters) below the water level?

I don't know psi - but the standard scuba divers tables put the pressure at
6 meters as 1.6 bar (1.6 x average pressure at the surface). 
I'm no expert on brachiosaur physiology, but to be able to breath at this
depth would require massive intercostal and other chest muscles, and a
heavily reinforced windpipe - at least at it's base.
Whatever about the windpipe, we should be able to see some indication of
unusually large chest muscles, from their attachment sites - is there
evidence of this?

>Second, it has been stated recently on this list that a fast running
_Tyrannosaurus
>rex_ individual (was it 20 meters per second?) would trip and fall on its
skull
>with the force of a bus impacting a brick wall at approximately 60 mph.  I
>understand such a hypothetical tyrannosaur was calculated to have sustained
fatal
>injuries.  My question: is the 60 mph bus analogy apt?

This sounds a little far fetched. To start with 20m/s is a too quick for a T
Rex. It works out at 72km/hr or 45 mph. Perhaps 15m/s is more realistic
(about 33-35 mph). Also most buses weigh a lot more that a Tyrannosaur. If
we assume that our T Rex is about 2 metric tonnes - sprinting at 15m/s into
a brick wall will have a collision force of about 30 kiloNewtons.
If it tripped up and simply fell on the ground, all that force would be used
up in skidding to a halt on it's chest or side. Lots of scrapes, but I can't
see it being fatal.
As a final thought - how could a creature have been successful if it had a
significant risk of death every time it sprinted after it's dinner?
"Nature" doesn't design things that badly.

John