The pelvis (hip) is large, with the upper portion formed by a rod-shaped ilium and the lower portion formed by a narrow and long "puboischiadic plate". The rear portion of the puboischiadic plate is particularly elongated in "Westlothiana" compared to in other reptiliomorphs, but the other parts of the pelvis are fairly normal by the group's standards. The femur is long and robust, and is also thinnest in the middle as with the humerus. Also similar to the humerus, the femur's crests and roughened areas for muscle attachment are large considering the small size of the animal. Although the femur is generally similar to that of synapsids, the tibia and fibula are much more simple and primitive. In addition, they are noticeably smaller than the femur, a condition reversed to the trend in most reptiliomorphs leading to amniotes.