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Re: Rex Fall part 2



[ I think after this I'm not going to accept *any* more messages that
  compare falling humans to falling Tyrannosaurs.  A major point that
  Jeff has been trying to get across is how important the difference
  in scale is.  People just don't seem to be getting that...  And thus
  we're not getting anywhere with this conversation any more.  -- MR ]

Nick Longrich and Peter Buchholz have said humans can make some falls a
lot easier.  I can think of three techniques.

A fourth-grade pal and I used to jump off my tree house.  He said it was
better to roll when we landed.  That helped a lot.

Kinetic energy is force x distance.  Because human legs get weaker as
they bend, we had to absorb most of our fall without letting our legs
collapse far - 8 inches?  If we had to stop a 10-foot fall in 8 inches,
that would have been 15 g, quite a jolt.

Rolling allowed our center of mass to drop a lot farther as we absorbed
the fall with legs, a knee, a hip, an elbow, and a shoulder.  The
greater distance meant less force was required.

Perhaps T Rex had a landing maneuver with an analogous kind of
crumpling. 

I once worked as a martial-arts dummy.  This entailed being thrown over
someone's shoulder or hip and slammed to the ground.   Surprisingly,
being slammed down for two hours at a time wasn't bad at all.  That's
because I was warned to slap the ground just before I hit.

The arm can absorb a much bigger jolt than some other parts of the
body.  Slapping the ground transfers a disproportionate share of a
fall's energy to the arm, allowing the torso and head to land more
gently.  Slamming my feet against the ground also helped, but that only
worked if I was being thrown flat on my back.

T Rex's tail would seem like a great organ to absorb a fall by slapping
the ground.  Because he lacked long arms, I don't know just how he might
have used his tail this way.  

Running would have made T Rex's falls more dangerous.  What hobo would
dare jump from a speeding train?  Doesn't landing in the wind kill
parachutists?  Don't videos of Evel Knievel show how violently a person
can tumble after falling from a motorcycle?

Almost 30 years ago, I hit a harmless-looking puddle while rounding a
corner on a motorcycle at 30 mph.  The weather was so warm that I was in
shirt sleeves.  I didn't realize there was frost in the ground.  Ice had
formed on the bottom of the puddle.

The motorcycle was gone in a flash.  As I somersaulted down the street,
my motorcycle slid alongside, throwing up a shower of sparks.  We came
to a stop together, 70 feet down the street.  I must have tumbled ten
times, absorbing the energy from my initial ground speed.  

If I'd hit wrong, I might taken a neck-breaking flip.  By keeping
everything tucked in, I came through without even abrasions on my skin
or clothes.  An arm can be a big advantage in an ordinary fall, but that
experience left me feeling that it could be fatal to use an arm in a
high-speed tumble.

I agree with LN Jeff's arguments and his evidence.  How could T Rex have
been a runner?  OTOH, I think he was a runner, although this puzzles
me.  T Rex's tiny arms indicate to me that this animal must have
specialized in handling high-speed tumbles.

Oh yes - the fore-and-aft length of T Rex would have helped him avoid
falls by making him slower to pitch forward, much as a tightrope walker
can use a pole for stability from side to side.

- Stephen Throop