A computational model is used to estimate three-dimensional pelvic muscle moment arms for the saurolophine hadrosaur Edmontosaurus. The results are compared to models of the ornithischians Lesothosaurus and Kentrosaurus, the crocodilian Alligator, and the theropod Allosaurus in order to examine changes related to the evolution of quadrupedalism and to set the results in an evolutionary context. Edmontosaurus and Kentrosaurus generally had higher flexion moment arms than the other taxa, suggesting a correlation with ornithischian quadrupedalism. Edmontosaurus had relatively high flexor and extensor moment arms compared to other dinosaurs, which could indicate increased locomotor performance in conjunction with decreased femoral excursion relating to a flexed hind limb stance. Alligator had the lowest flexion-extension and abduction moment arms and the highest adduction moment arms of all taxa modeled. Differences between Alligator and the dinosaurs probably reflect the different gaits utilized by these taxa. Dinosaurs use an upright gait emphasizing flexion and extension, while in the sprawling gait of Alligator, long-axis rotation and abduction-adduction joint excursions are also important. High adduction moments in Alligator can be attributed to the control of abductor moments generated around the hip by the ground reaction force acting on the horizontal femur; in contrast, adductor moments are generated around the hip in dinosaurs, and are controlled using abductor musculature.