Australopithecus afarensis

Exemplar: A.L. 444-2 [Hadar] - 3.0 million y.a.

AUSTRALOPITHECUS AFARENSIS, which lived from 3.9 to 3.0 million years ago, is one of the first species to appear after the split between emerging hominids and ancestor chimpanzees. It seems to descend directly from Australopithecus anamensis, a species of large ape that lived from 4.2 to 3.9 million years ago.

Not surprisingly, there are several points of resemblance between the afarensis and chimpanzee skulls: a wide, apelike face with a low forehead, bony browridges, flat nose, protruding upper jaw, and a massive lower jaw with large back teeth. (The pointed canine teeth, missing from the afarensis fossil, were smaller than those in modern apes.) Both have a brain volume of around 480cc. The shape of the jaw is intermediate between the rectangular shape of apes and the parabolic shape of humans.

As the size of the skull shows, afarensis was a larger animal than the chimpanzee. Males weighed about 45 kilograms and stood about 1.5 meters tall. Females were much smaller, at about 30 kg and 1.1 meter tall -- the largest sexual dimorphism of any hominid or prehominid species.

The larger australopithecine body included changes to the spine, pelvis and leg joints that make walking an effective form of locomotion. Though still capable of climbing and resting in trees, a habitual bipedal posture freed the hands to manipulate, carry and throw objects. Though the finger and toe bones are curved and proportionally longer than in humans, afarensis hands were similar to humans in most other respects.

Afarensis survived for almost million years, longer than any other hominid except perhaps Homo erectus. The direct ancestor of both the hominids and all the larger ("robust") australopithecines, afarensis is generally regarded as the founding species of the hominid evolutionary line.