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Re: Rex Fall part 2

Jeff Martz wrote:

>     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. 

The same can be said for any body maneuvers to minimize impact damage.
I'm not suggesting that T.rex could do a shoulder roll (!), but it
could, perhaps, roll onto its side, for instance. Pushing with the far
leg and rolling onto one side could well convert vertical momentum
into horizontal. Many animals (of admittedly much less mass!) are
pretty adept at using rolling maneuvers.

>     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.

Personally, I suspect T.rex went pretty much where it wanted, like a
modern lion moves easily from jungle to savannah. But it might very well
have found the hunting easier where the forest offered cover.

>     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 
>     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?

Fighter pilots routinely sustain forces well in excess of 6g for
periods of seconds at a time, rather than just a momentary
impact. While T.rex presumably had a far greater ratio of mass to
structural strength (since doubling dimensions increases strength by a
factor of four, but mass by a factor of eight), we also have to
consider that it had another leg, presumably still on the ground, with
which it could apply force to minimize the impact.
        And, instincts being what they are (and presumably were),
don't you think Rex would use its tremendous neck muscles to begin
decelerating its head as soon as its torso hit? You can't just
"seperately" drop torso and head -- they're still connected.  The head
may have avoided impact entirely.
        I'm not saying the calculations are wrong. I'm just saying
that you can't just <DROP> a living animal, any animal, and expect it
to fall like so much inert mass.  I can calculate forces for dropping
a cat on concrete, and show why it should break its skull, but I doubt
that the experiment would ever go like the calculations.
        Finally, I notice that a broken AND HEALED leg is on Sue's
litany of war wounds.  I've never seen a biped that didn't fall when
one of its legs was broken.  Evidently Sue hadn't read the
calculations of Farlow et al, or she would have known she should have
died then.

Wayne Anderson