Palaeoanthropologists divide the australopithecines into two groups – the gracile australopithecines and the robust australopithecines. Some assign the robust australopithecines to their own genus, called Paranthropus, to distinguish them from the gracile australopithecines.

There are three species of robust Australopithecus:

• Australopithecus aethiopicus, 2.7 -2.3 million years ago (Ma), East Africa
• Australopithecus robustus, 1.7 Ma, South Africa
• Australopithecus boisei, 2.3-1.4 Ma, East Africa

Robust australopithecines are morphologically distinguished from gracile australopithecines by these features:

• The skull is larger and consists of thicker and more robust bones.
• Male skulls exhibit a sagittal crest.
• The molars and premolars are extremely large.
• The cheek bones (zygomatic arches) are large and flaring, giving the face a very wide appearance.

Robust Australopithecines Had a Tough Diet

Most of the features that distinguish robust australopithecines from gracile australopithecines are indicative of a diet high in tough, fibrous foods that require a lot of chewing. The sagittal crest along the top of the skull provides a larger muscle attachment site for the temporalis muscle, which is important for chewing. The large, flaring zygomatic bones would have wrapped around these large temporalis muscles. The extremely large molars and premolars offered a larger surface area for crushing and breaking down tough foods, like nuts, seeds, and uncooked tubers.

Robust Australopithecus Co-existed with the Genus Homo

Robust australopithecines and the earliest members of our own genus, Homo, both inhabited the African landscape between about 2.3 Ma and 1.4 Ma. Some anthropologists think that robust australopithecines avoided competing directly with early Homo because of their specialized diet focused on plant remains.

Robust Australopithecus and Tools?

The first stone tools appear 2.6 Ma. They come from the site of Gona, Ethiopia in East Africa. It is notoriously difficult to associate tool assemblages with certain hominin species. It is argued by some that the first stone tools were manufactured by robust australopithecines that inhabited this landscape at the same time. Others argue that the first stone tool manufacturer was Homo habilis, the earliest member of our own genus, even though the earliest dated Homo fossils as of yet come from sediments dated to about 2.3 Ma.

Evidence for the use of bone tools by robust australopithecines comes from the sites of Swartkrans, Sterkfontein, and Drimolin in South Africa. The Australopithecus robustus population represented in this region about 2 -1.5 Ma may have used bone tools for digging into termite mounds.

The Robust Australopithecines Were an Evolutionary Side Branch

Around 1.4 Ma, robust australopithecines went extinct. No one can ascertain the reason for this, but it may be that their diet was so specialized that it could not adapt quickly enough to climatic events associated with that time period. In contrast, the genus Homo is considered more of a generalist – focusing on different types of resources that included a greater variety of plant and animal remains – and their behavioral adaptability may have permitted their survival through the Pleistocene.

Sources:

Backwell, L. and F. d’Errico, 2008. “Early hominid bone tools from Drimolen, South Africa.” Journal of Archaeological Science 35(11):2880-2894

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.

Tree of Life Web Project: Evolution of the Australopithecines

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