Evolution: Ancient SA ear bones shed new light on apes and bipeds

2013-05-16 00:00

CAPE TOWN — The three smallest bones in the body — the fragile middle ear bones — have been found whole in a South African hominin fossil.

The find is one of the most remarkable yet, as there are fewer than 10 of these tiny bones in the fossil record — of which five are in South Africa.

A multi-national research team, lead by Dr Darryl de Ruiter, examined the skull of a hominin at Wits University. The skull, believed to be about 1,9 million years old, had been found in a cave called Swartkrans in the Cradle of Humankind.

De Ruiter, a professor in the Department of Anthropology at Texas A&M University, said of particular interest to the team were the tiny bones found in the middle ear of the species Paranthropus robustus , especially one called the malleus.

The malleus and the other ear bones — the incus and the stapes — together show a mixture of ape-like and human-like features, and represent the first time all three bones have been found together in one skull.

De Ruiter said the discovery was important for two reasons.

“First, ear ossicles are fully formed and adult-sized at birth, and they do not undergo any type of anatomical change in an individual lifetime. Thus, they are a very close representation of genetic expression.

“Second, these bones show that their hearing ability was different from that of humans — not necessarily better or worse, but certainly different.”

He explained that bipedalism (walking on two feet) and a reduction in the size of the canine teeth have long been held to be hallmarks of humanity, since they seem to be present in the earliest human fossils recovered to date.

“Our study suggests that the list may need to be updated to include changes in the malleus as well.”

De Ruiter and his fellow researchers published their findings in the science journal Proceedings of the National Academy of Science .

The team was funded by the National Research Foundation of South Africa and by the Ray A. Rothrock Fellowship at Texas A&M.

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