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Re: Airbagged(was Dive!Dive!Dive!)

Rob Meyerson wrote:

> If I recall from when we had this discussion last year, someone mentioned
>  that when an ostrich stumbles, it orients its body so it will land on it's
>  side.   When it hits the ground, it expends the excess inertia by
>  continuing to roll across the backbone, and onto it's other side (where it
>  could easily get back on it's feet).  Perhaps T. rex used a similar
>  strategy.  Twisting it's body sideways and rolling over it's spine to
>  prevent a fatal fall.

     I'm afraid I don't have any hard data to back this up, but I'd 
expect the difficulty of such a manuver increases with size.   I have a 
hard time imagining an elephant sized animal rolling over when it falls.   
It almost seems like a manuver like that would stress skeletal strength 
for such a large animal more then falling. 
> Then again, perhaps the "Louisiana bayou" environment allowed for soft
>  landings, further preventing any real damage being done from a fall.

      The paper did consider the relative softness of ther ground, and 
allowed that soft enough ground might prevent a fatal impact.  However, 
keep in mind that even  if the ground was soft enough to prevent 
immediate death, this would not necessarily preclude serious injury.  
Also, a "Louisiana Bayou" (Kirk Johnson, a DMNH paleobotanist 
who does a great deal of work with Hell Creek plants likens  
it more to a temperate Connecticut forest) environment is going to have a 
lot obstacles to trip on, and it might also be difficult to pick up 
speed in a forested environment.
     As a biped, a T.rex is going to have a greater likelyhood of 
falling if it trips then a quadraped or a biped with arms large enough  
to catch itself.  Also, even if it wasn't killed by the fall, a falling 
biped that recovers without a scratch is no more likely to catch the prey it 
was chasing then one that was killed.  By the time it picked itself up, 
the prey would be way ahead.  
     If a T.rex were to ambush a somewhat speedy prey animal and didn't 
catch it before it picked up speed, it might be better to give up and 
try again to risk serious injury keeping chase.  As already noted, most 
modern predator ambushes end in failure anyway.  
     All in all, I just think that given:
1) T.rex lived in a forested environment with quite a few potential 
obstacles, and which might make it difficult to pick up speed compared to 
a flat, open area.
2) Some anatomical evidence (femur strength and the relative shortness of 
the metatarsals) seems to indicate that T.rex wasn't incredibly speedy.
3) The significant likelyhood and risks of T.rex falling increasing with 
speed, and
4) The fact that they larger animals of T.rex's environment might have 
the same problems in the dealing with environmental obstacles as T.rex, 
and also generally had shorter legs anyway,
    I tend to lean toward the idea that T.rex was not a high speed runner 
or sprinter.  What is so sluggish about 12-15 mph anyway?
LN Jeff