HUTCHINSON, J.R.: 2-D quasi-static simulations of stance and gait in Tyrannosaurus and other tetrapods

Could the hindlimb muscles of a massive biped such as Tyrannosaurus support the stresses of running? I report preliminary results from biomechanical computer simulations of the net muscle moments required to maintain static equilibrium during bipedal standing (with extrapolations to mid-stance of walking and running) in Alligator, Gallus, Homo, Tyrannosaurus, and other tetrapods. Using data such as body segment dimensions, joint angles, and muscle architecture, I model how much volume of hindlimb muscle must be active to balance the moment of the ground reaction force at each joint. The models predict that the net muscle moments that the hindlimb muscles of Alligator can generate could not support bipedal running, whereas Gallus and Homo require a fairly low volume of active hindlimb muscle even to run. Thus my simulations compare favorably with data from living subjects. My models of Tyrannosaurusin various stances estimate that a huge volume of active hindlimb muscles would be required for running. In preliminary analyses, roughly 20-30% of the body mass would need to be hindlimb joint extensors. The knee joint moment is especially sensitive to the stance that is input. Was there sufficient hindlimb muscle volume to allow running in Tyrannosaurus? I demonstrate what assumptions must be made to conclude either that Tyrannosaurus lacked sufficient muscle volume for running, or that it did have sufficient musculature. This shows how sensitivity analysis of unknown variables is vital for quantitatively bounding the range of possible locomotor performance in extinct organisms and for minimizing speculation.