Epipubic bone

According to this hypothesis, the epipubic bones act as levers to stiffen the trunk during locomotion, and aid in breathing.

[4] Others have suggested that epipubic bones may constrain asymmetrical gaits, although this appears not to be the case.

[5] Only placentals, and possibly the early mammaliformes Megazostrodon and Erythrotherium, lack them;[6] in thylacines and sparassodonts, they appear to have become primarily cartilaginous and the osseous element has become strongly reduced or even absent.

[10] In modern marsupials, the epipubic bones are often called "marsupial bones" because they support the mother's pouch ("marsupium" is Latin for "pouch"), but their presence on other groups of mammals indicates that this was not their original function, which some researchers think was to assist locomotion by supporting some of the muscles that flex the thigh.

[12] However, vestiges of the epipubic bone may survive in a common placental characteristic, the baculum.