Rex Fall part 2

[Jeffrey Martz <martz@holly.ColoState.EDU>]

     If T.rex fell staight forward rather than on its side (which it 
probably would due to momentum), that "streamlining" would do it more harm 
than good.  T.rex was a pretty narrow animal compared to an African 
elephant of the same mass.  While an elephant could distribute the force 
of impact across its "blocky" body, T.rex would get it concentrated on a 
relatively narrow area, which would be more damaging.  
     Before we get into the calculations I'd like to make two important 
points.  First, T.rex would not have to "consciously" moderate its speed any 
more than a bird consciously avoids trying to fly through trees or you or I 
have to consciously pull our fingers off a hot stove.  Self preserving 
instincts can be selected for like any morphological trait.  
     Second (Farlow et all also make note of this)  T.rex is beleived to 
have inhabited a forested environment.  This might make:
a) close range ambushes easier (no need for extended chases)
b) more difficulty in getting up to speed, for both predator and prey
c) more potential obstacles to trip over.
     If a T.rex were to ambush its prey and didn't catch it before the 
prey got up to speed, the dangers of running faster and possibly 
suffering a seriously damaging or fatal fall in an obstacle laden 
environment like a forest might well exceed the benefits of 
catching that particular animal (you don't see lions trying to kill a 
fully adult elephant just because it would provide a lot of meat).  The 
predator can always try again.  Most predator-prey chases with modern animals 
end with failure for the predator anyhow.        

CALCULATIONS:

VERTICAL COMPONANT OF IMPACT FORCE:

     Ignoring for a moment forward momentum and just dropping our T.rex 
for no particular reason where it stands, the force of impact can be 
calculated by using the mass of the animal's head and/or torso (depending 
on damage to which you want to look at) and the distance said head and/or 
torso has to fall.  The force of impact is also going to be recuced by 
how far the animal's body depresses into the ground (as a direct result of how
soft the ground is). Farlow estimated head height at about 4 meters (12 feet) 
and torso height at 1.46 meters (about 4'4").  He unfortunatly doesn't give 
his mass estimates he used for just the torso or head.  He assumed the 
ground was moderatly soft, but not really soft and muddy. His numbers are as 
follows:
     Vertical force acting on torso: 260,000 newtons
                                     deceleration: 6g
     Vertical force acting on head: 99,000 newtons
                                    deceleration: 14g
     T.rex skull flexion may be unknown, but how much is a few inches 
worth of skull flexion going to offset this kind of impact?
 
Farlow et all were charged with not taking into account forward 
momentum in thier equations.  This is not the case.  They calculated a 
few models involving skidding and skid distances, and the effects 
these would have on impact forces.  I was going to clip those onto this 
message, but I'm in a rush right now so it will have to wait until later 
today, if not sometime this week.
     
     I would also like to point out that an animal streamlined while 
standing and holding its body horizonal is not going to be so streamlined 
flopped over and digging its face and body into the ground.  Take a model 
airplane, tilt it at an angle, and drag it across the ground, and I think 
you will find its streamlining isn't going to make it travel more smoothly.

LN Jeff
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