Epipubic bones

Epipubic bones are a pair of bones which project forward from the pelvic bones of modern marsupials and of some fossil mammals - multituberculates, monotremes, and even eutherians (the ancestors of placental mammals).

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 pull the thigh forwards.

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