Constraint-based exclusion of limb poses for reconstructing theropod dinosaur locomotion

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Abstract
Plausible poses were identified for the hind limb of Tyrannosaurus rex and three other non-avian theropod dinosaurs at mid-stance of locomotion using constraint-based exclusion. This new method, validated by analysis of two species of birds, involves applying demonstrably realistic geometric and kinetic (force-based) constraints from extant animals to exclude, rather than include, potential poses. Starting with a “configuration space” of millions of candidate poses, we used a step-wise series of criteria to constrict the volume to a small subset of solutions, which can serve as starting points for reconstructing complete stride cycles. It was found that the maximum relative mid-stance limb force, as well as the relative number of configurations at lower forces, decreased with increasing body size. Constraint-based exclusion restricted Tyrannosaurus to a narrow region of neither very columnar nor very flexed poses that may have allowed relatively slow running, but no reasonable combinations of inp...