The gracile australopithecines inhabited Africa between 4 and 2 Million years ago (Ma). Our own genus, Homo, descended from one of the gracile Australopithecus species.

The australopithecines are generally divided into two groups – the gracile australopithecines and the robust australopithecines. The robust australopithecines are assigned their own genus by some researchers (Paranthropus) to distinguish them from the gracile australopithecines.

There are at least five species of gracile Australopithecus:

• Australopithecus anamensis, 4.2 -3.9 Ma, East Africa
• Australopithecus afarensis, 3.6-2.9 Ma, East Africa
• Australopithecus (or Kenyanthropus) platyops, 3. 5 Ma -3.2, East Africa
• Australopithecus africanus, 3-2 Ma, South Africa
• Australopithecus garhi, 2.5 Ma, East Africa

Australopithecines are morphologically characterized by these traits:

• The morphology of the pelvis, legs, and spine is adapted for bipedal locomotion.
• The lower arm is long relative to later hominins and modern humans.
• Australopithecines are small in stature compared to modern humans (about 4 ft. tall).
• Their brain size is similar or slightly bigger than chimpanzees (cranial capacity is 350 cc – 600 cc).
• They have large molar teeth with thick enamel.
• They have small canine teeth compared to the non-human apes.

The Taung Child – The First Australopithecine Fossil Discovered

In 1924, Raymond Dart discovered the first Australopithecine fossil at a site called Taung, South Africa. It was a partial skull and endocast of the brain case of a 3 year-old child. He assigned the specimen to a new species Australopithcus africanus, meaning “southern ape of Africa”.

It took a while for the scientific community to accept the validity of Dart’s claim. Scientists expected the so-called “missing link” to have evolved a big brain before developing the other human characteristics like small canines and bipedal locomotion. Also, no one at that time was expecting the earliest known human ancestor to come from Africa. All previous finds of human ancestors had been discovered in Europe and southeast Asia. Now several australopithecine finds are known from both East and southern Africa.

Australopithecines Inhabited Diverse Environments

For a long time, researchers thought that the origins of bipedalism in the human lineage was linked to the spread of savannah grasslands in Africa. Now, palaeoenvironmental interpretations based on the types of plants and animals found in association with early hominins reveal that the first bipeds actually inhabited wooded environments. Australopithecus anamensis also seems to have inhabited wooded environments.

A. afarensis and later australopithecines lived in various habitats. Pollen studies reveal that the environments at australopithecine sites range from open grasslands to more forested environments. The skeletal morphology of australopithecines (long arms, curved fingers) suggests they were adapted to climbing trees. Traces of wear on the teeth of some fossils reveal that gracile australopithecines had a varied diet that may have included leaves, grasses, nuts, seeds and fleshy fruits. The “savannah hypothesis” does not seem to hold up.

Who was the Ancestor of Early Homo?

It is difficult to determine evolutionary relationships based solely on fossil remains, but some researchers feel that A. garhi is ancestral to the genus Homo. A. garhi’s leg bones are longer thanA. afarensis, suggesting a more human-like body plan. There is also a possibility that A. garhimanufactured the first stone tools that date to the same time period at 2.5 Ma.

For more articles in the Early Humans series, click here.

Sources:

Klein, R. G., 1999. The human career: human biological and cultural origins. University of Chicago Press., Chicago

Larsen, C.S. 2008. Our Origins: Discovering Physical Anthropology. Norton and Company: New York, NY.

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