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RE: Lack of Running Giant Theropod Tracks



I've read two of Hutchinson's papers so far and I found them very
interesting, but I think the media (and most people in general) seem
to think that studies or experiments equal "proof". The reality is
there is no such thing as "proof" in science (outside of
mathematics), only evidence. I imagine John Hutchinson would be the
first to tell you that there are a *lot* of unknowns when forming
computer models of an animal that has been dead for 65 million
years. That being said, 25 mph isn't exactly walking, it's actually
pretty fast. I would be interested to see how models would turn out
if they included highly elastic tendons somewhat like those seen in
macropods (kangaroos), which seem to hold up well under increased
weight. I'm sure that was factored in to some degree since most or
all tendons and muscles can work like springs. I'm also stumped as to
how a 100 ton sauropod could support its weight if a tyrannosaur had
just enough strength in its legs to walk quickly (10-15mph ) and not
run.

As co-author of one of the papers I'd like to remark on the tendon
thing because it seems to come up quite often: The clever thing John
did was to focus on the force at the mid-stance moment. The energy
storage due to elastic tendons will not help you there, because the
tendons are still attached to muscle which must still exert the
necessary force. What tendons *could* to is to change the typical
sinusoidal shape of the ground reaction force curve to something
different that rises more steeply and so covers more area (giving a
larger mean force) without increasing the maximum. We did some
back-of-the-envelope calculations on this - the maximum GRF will not
increase by more than roughly 20% IIRC.

Of course there are lots of unknowns and uncertainties in the
calculations (and John will be the first to admit that), but the basic
result that very high speeds will not be possible looks quite robust
to me. (But having a 6-ton theropod run at you at 25mph would probably
convince you that this is not really slow...)

BTW, the leg proportions of ornithopods seem to be less well-adapted
to fast running than those of T rex, so even if T rex was not a
super-sprinter, it may still have been fast enough. (And of course
there are scenarios where the juveniles do the running, and at 2 tons
of mass the pciture changes quite a bit.) If anybody has reasonable
measurements and estimates for muscles in ornithopod legs, we could
easily run them through our software...

Cheers,

Martin.

                   Priv.-Doz. Dr. Martin Bäker
                   Institut für Werkstoffe
                   Technische Universität Braunschweig
                   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>