Australopithecus

ANAMENSIS [right) lived roughly four million years ago. Only a few anamensis fossils have l j. been found—the ones i shown at the left V , include a jawbone and

: part of the front of the face [left), parts of an arm bone [center) and fragments of a lower leg bone (right)—and thus researchers cannot determine much about the species' physical appearance. But scientists have established that anamensis walked upright, making it the earliest bipedal creature yet to be discovered.

A new species of Australopithecus, the ancestor of Homo, pushes back the origins of bipedalism to some four million years ago

By Meave Leakey and Alan Walker those of modern apes in that they hardly projected past the rest of the tooth row. The younger of the two species, A. robustus, had bizarre adaptations for chewing—huge molar and premolar teeth combined with bony crests on the skull where powerful chewing muscles would have been attached.

Paleoanthropologists identified more species of Australopithecus over the next several decades. In 1959 Mary Leakey unearthed a skull from yet another East African species closely related to robustus. Skulls of these species uncovered during the past 45 years in the northeastern part of Africa, in Ethiopia and Kenya, differed considerably from those found in South Africa; as a result, researchers think that two separate robus-tus-like species—a northern one and a southern one—existed.

In 1978 Donald C. Johanson, now at the Institute of Human Origins at Arizona State University, along with his colleagues, identified still another species of Australopithecus. Johanson and his team had been studying a small number of hominid bones and teeth discovered at Laetoli, as well as a large and very important collection of specimens from the Hadar region of Ethiopia (including the famous "Lucy" skeleton). The group named the new species afarensis. Radio-metric dating revealed that the species had lived between 3.6 and 2.9 million years ago, making it the oldest Australopithecus known at the time.

This early species is probably the best studied of all the Australopithecus recognized so far, and it is certainly the one that has generated the most controversy over the past 30 years. The debates have ranged over many issues: whether the afarensis fossils were truly distinct from the africanus fossils from South Africa; whether there was one or several species at Hadar; whether the Tanzanian and Ethiopian fossils were of the same species; and whether the fossils had been dated correctly.

But the most divisive debate concerns the issue of how extensively the bipedal afarensis climbed in trees. Fossils of afarensis include various bone and

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