 The decreasing width of the legs in later species and the reduction of the iliac crests of the pelvis indicate less reliance on them for support—relying more on buoyancy—and the animal probably preferred to sit semi-submerged in the water while resting.The legs also became more flexible, with later species able to, at maximum extension, have the femora reach a horizontal position parallel to the torso.The femur and kneecap are smaller in "T. yuacensis" than in "T. natans".