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Re: Sufferin' Sauropods




Jaime Headden wrote:
> that sauropods moved <3 mph trackways,
> where it would be easy to _out-walk_ them, contra the fast-moving
> "mamenchisaur" from _the Lost World_, so this removes the possibilities of
> "accidentally" tripping because they're too fast and can't balance
> themselves in time.
Some time ago, I made the following observation about tripping in big
animals, which, at that time, went unanswered. Perhaps someone has a
comment on it now? At the time, I looked for arguments why the stride
frequency is smaller (i.e. strides are quicker) in smaller animals:


If you are not running on very smooth
ground, you will have to adjust your movements to the stumbling stones you
encounter, otherwise you will frequently land on your nose. Now the time
you have to recover from stumbling or to adjust to uneven ground, is
obviously proportional to the time you have until you belly hits
the ground, i.e. until your center of mass has fallen a certain distance.
This time scales like

t ~ sqrt(l/g) (l is your height and g the earth gravity field
               acceleration)

so it gets shorter, the smaller you are. So a slow-going mouse will have
to react VERY quickly whenever the ground is uneven, even if it would like
to be slow. (If you ever hiked in the mountain, you have perhaps noticed
that sometimes it is indeed easier to go more quickly on uneven ground, so
as not to have to make quick adjustments during slow moving). So I argue
that for efficient locomotion your stride frequency must be not much
slower than the reaction time you need. Now this argument I also never saw
before
- is it again something only a stupid physicist can cook up, with no
relation to the real world?

If not, it has another interesting aspect: It has been argued that a T rex
cannot have run because it would severly injure itself on falling.
However, as it is so big, it would have a lot of time to catch itself,
when stumbling. So perhaps, the T rex simply did not fall, because for it
the reaction time was quite large.


Any ideas on this?


                   Dr. Martin Bäker
                   Institut für Werkstoffe
                   Langer Kamp 8
                   38106 Braunschweig
                   Germany
                   Tel.: 00-49-531-391-3073
                   Fax   00-49-531-391-3058
                   e-mail <martin.baeker@tu-bs.de>