[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Power-walking tyrannosaurs



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.


--------------------------------------------------------------------
mail2web.com ? What can On Demand Business Solutions do for you?
http://link.mail2web.com/Business/SharePoint