We created a musculoskeletal model of the Tyrannosaurus Rex lower extremity that includes 10 degrees of joint freedom (flexion/extension, ab/adduction, and medial/lateral rotation) and 33 main muscle groups crossing the hip, knee, ankle, and toe joints of each hindlimb. The model was developed by acquiring and processing bone geometric data, defining joint rotation axes, justifying muscle attachment sites, and specifying muscle-tendon geometry and paths.
Sagittal view of the T-rex model. By analyzing the moment arms predicted by the model, we found that more upright poses would have improved mechanical advantage of the muscles considerably. Our results suggest that T. rex did not have the allometrically large muscle moment arms that might be expected in a proficient runner. The information provided by the model is important for determining how T. rex stood and walked, and how the muscles of a 4000-7000 kg biped might have worked in comparison with extant bipeds such as birds and humans. Our model thus strengthens the conclusion that T. rex was not an exceptionally fast runner, and supports the inference that more upright (although not completely columnar) poses are more plausible for T. rex. These results inform general principles about the relationship between size, limb orientation, and locomotor mechanics: exceptionally big animals have a more limited range of locomotor abilities, and tend to adopt more upright poses that improve extensor muscle effective mechanical advantage.
Hutchinson, Anderson, Blemker, and Delp. "Analysis of hindlimb muscle moment arms in Tyrannosaurus rex using a three-dimensional musculoskeletal computer model: implications for stance, gait, and speed." Paleobiology, 2005. (Download PDF)