A Star Species
Evidence is rare for many early hominid species. But in the case of Australopithecus afarensis, which lived between four and three million years ago, researchers have found hundreds of fossils from dozens of individuals--so this species is one of the best understood of the early hominids. Fossils such as the skull, knee joint and jaws displayed in the hall reveal a creature still apelike in many ways, yet able to walk upright when on the ground.
Examine the Evidence: Leg bones
Compare the ancient leg bones of Australopithecus afarensis (right) with the leg bones of a chimpanzee (left) and a modern human (center). Was the ancient hominid bipedal--that is, did it walk on two feet?
- Thigh bone is angled; knee and foot are near the midline of the body. Humans have an efficient upright bipedal stride. human
- Thigh bone is not angled; knee and foot are farther from the midline of the body. Chimps waddle when trying to walk upright. chimp
- Thigh bone is angled. hominid
An Unfamiliar Face
Unlike modern humans, Australopithecus afarensis had a projecting face and large jaws.
At Home in the Trees
Although Australopithecus afarensis walked upright when on the ground, this hominid was still very apelike in certain ways. Members of this species probably spent part of their time in trees, finding food and shelter there.
In 1978, paleoanthropologists working in eastern Africa were thrilled to discover a trail of ancient human footprints at the Laetoli site in Tanzania. These tracks capture forever a moment of human history, when some 3.6 million years ago, two early hominids, probably members of the genus Australopithecus, walked upright across the African plain.
How Do We Know?
A topographic map of the Laetoli footprints shows they were made by a hominid with a pattern of walking similar to that of modern humans. The heel struck the ground first, and at the end of the step, the hominid pushed off with the big toe. The two sets of tracks match pace for pace and are only about 30 centimeters (12 inches) apart, so the hominids may well have been walking side by side.
Examine the Evidence: Footprints
- big toe is in line with other toes
- foot is arched
- impression is deep at the heel, indicating the heel struck the ground first
- impression is deep at the big toe, indicating the hominid pushed off from the big toe at the end of each step