Biomechanical reconstruction is increasingly being applied to the study of the mode of life of fossil animals. Different footprints from the fossil mammal Megatherium sp., the giant ground sloth, seem to indicate that it was able to use either bipedal or quadrupedal locomotion. By means of the estimation of the body mass of the type of the species Megatherium americanum, and using the published tracks, different mechanical parameters, such as speed, Froude number, indicators of athletic ability and bending and resistance moments of the vertebral column were calculated in both bipedal and quadrupedal conditions. Results on leg parameters are not conclusive as to the kind of locomotion to which Megatherium sp. was better adapted, but the calculations on the moments of resistance of the vertebral column and on the bending moment at breaking of the femur seem to indicate that Megatherium sp. presented adaptations to bipedalism.MEGATHERIUM, mammals, legs, vertebral column, locomotion, biomechanics, reconstruction.