Hip bone The hip bone first appears in fishes, where it consists of a simple, usually triangular bone, to which the pelvic fin articulates. The hip bones on each side usually connect with each other at the forward end, and are even solidly fused in lungfishes and sharks, but they never attach to the vertebral column. In the early tetrapods, this early hip bone evolved to become the ischium and pubis, while the ilium formed as a new structure, initially somewhat rod-like in form, but soon adding a larger bony blade. The acetabulum is already present at the point where the three
Aphanosauria bone, although perhaps a small portion was open according to a notch near where the ischium contacts the illium (upper blade of the hip). The gracile femur (thigh bone) of aphanosaurs possesses a characteristic set of features which can be used to diagnose the group. The proximal (near) surface of the bone, which connects to the hip socket, has a deep groove on it, rather than simply being a flat articulation surface. In addition, the bone's distal (far) articulation, which connects to the lower leg bones, is concave. The proximal part of the femur also has several bumps (tubers) on