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Re: Power-walking tyrannosaurs



Congrats Heinrich! Looks like this is making a splash!

Viv

On 8 November 2011 04:53, bh480@scn.org <bh480@scn.org> wrote:
> From: Ben Creisler
> bh480@scn.org
>
> An online article on the Nature site and the abstract from the SVP,
> challenging Alexander’s calculations for theropod locomotion:
>
> Tyrannosaurs were power-walkers
> http://www.nature.com/news/2011/111107/full/news.2011.631.html
>
> MALLISON, Heinrich, Museum fr Naturkunde - Leibniz Institute for Research
> on Evolution and Biodiversity at the Humboldt University Berlin, Berlin,
> Germany
>
> FAST MOVING DINOSAURS: WHY OUR BASIC TENET IS WRONG
>
> Locomotion speeds of dinosaurs are often calculated from ichnofossils,
> using Alexander’s  formula that is based on data mainly from mammals and
> birds. Results indicate that dinosaurs were rather slow compared to
> mammals. Inaccuracies due to errors in hip height  estimates and other
> factors are expected, but the method is generally accepted to deliver at
> least "ballpark figures". However, in nearly all dinosaurs except theropods
> the hind limbs differ significantly from both mammals and birds in the
> distribution of maximal joint torques possible. Is it biomechanically sound
> to apply the formula under these circumstances? A detailed assessment of
> dinosaur limbs, using musculoskeletal modeling in SIMM and Computer Aided
> Engineering (CAE) kinetic/dynamic modeling, taking gravity, mass
> distribution and inertia into account, indicates that a basic tenet of
> Alexander’s formula, the proportional relationship between stride length
> (SL) and stride frequency (SF) seen in mammals and birds, is unlikely to
> have existed in non-theropod dinosaurs, and may have had an unusually low
> slope in theropods. This means that speeds calculated from tracks are the
> slowest speeds at which the animals have moved, but may be significantly
> too low. We may therefore not expect to gain information on the top speeds
> of dinosaurs from tracks at all. Skeleton-based analyses can suffer from
> similar uncertainties, because large limb excursion angles as seen in
> quickly moving mammals create high forces in the limbs. Usually, similar
> limb kinematics are assumed for dinosaurs. However, if dinosaurs combined
> high SFs with short SLs, they were able to move far faster for given
> maximal forces in the joints than previous models suggest. The modeling
> results from SIMM and CAE suggest that dinosaurs used much higher SF/SL
> ratios than mammals, achieving absolute speeds in walking gaits that force
> same-size mammals into running gaits.
>
>
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