Dinosaur biomechanics – Power-walking tyrannosaurs


An online article on the Nature site and the abstract from the SVP,
challenging Alexander’s calculations for theropod locomotion:

Tyrannosaurs were power-walkers

MALLISON, Heinrich, Museum fr Naturkunde – Leibniz Institute for Research
on Evolution and Biodiversity at the Humboldt University Berlin, Berlin,


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.