The study, published by the National Academy of Sciences, was conducted by anthropologist Rolf Quam from Binghamton University in collaboration with researchers from Spain, the U.S. and Italy.

One of the smallest bones in the human body are the ossicles, and are rarely found in the human fossils recovered. Unlike the other bones of the skeleton, the ossicles are completely formed and adult-sized at birth. This shows that both the size and shape of the ossicles are under high genetic control. Despite being the smallest bones, they carry loads of evolutionary information.

In the new study, the researchers analyzed several auditory ossicles of the early hominin species Paranthropus robustus and Australopithecus africanus. The study consisted of all the three ear bones i.e., the oldest complete ossicular chain of a fossil hominin. They were excavated from South African cave sites of Swartkrans and Sterkfontein, dating back to two million years ago.