Australopithecus africanus was an extinct hominin species from Southern Africa, living approximately 3.3 to 2.1 million years ago during the Pliocene epoch. This early human ancestor offers insights into the transitional phases between more ape-like forms and the emergence of the Homo genus. Its discovery influenced the understanding that bipedalism, or walking upright on two legs, predated the development of a large brain in the hominin lineage.
Unearthing the Past: Key Discoveries
The journey to understand Australopithecus africanus began in 1924 with Raymond Dart’s discovery of the Taung Child in South Africa. This fossilized skull of a juvenile, estimated to be around 2.8 million years old, exhibited a combination of human-like and ape-like features. Dart recognized the forward position of the foramen magnum, the opening where the spinal cord connects to the brain, as evidence of upright walking, a trait he linked to early human ancestry. He named the new species Australopithecus africanus, meaning “southern ape of Africa”.
Dart’s initial claims faced skepticism from the scientific community, which at the time largely believed that a large brain evolved before bipedalism and that human origins were outside of Africa. It took over two decades for his interpretation to gain widespread acceptance, largely due to further discoveries by Robert Broom and others. Broom’s work at Sterkfontein caves yielded more adult Australopithecus africanus fossils, including a nearly complete female cranium known as “Mrs. Ples” (STS 5) in 1947, which helped solidify the species’ place in the human family tree.
The Sterkfontein cave system, part of the Cradle of Humankind near Johannesburg, has been an abundant source of Australopithecus africanus fossils. Another significant find, “Little Foot” (STW 573), discovered between 1994 and 1997, represents the most complete Australopithecus skeleton ever found, with about 90% of the skeleton preserved. Initially dated to 3.3 million years ago, some researchers have redated “Little Foot” to 3.67 million years ago, making it the oldest Australopithecus specimen from South Africa.
Anatomy of an Early Hominin
Australopithecus africanus possessed a mosaic of anatomical features, displaying both ape-like and human-like characteristics. Evidence for bipedalism is strong, indicated by the forward placement of the foramen magnum at the base of the skull, similar to humans. Further support comes from the morphology of the pelvis, femur, and foot bones, which suggest an ability to walk upright.
Despite its bipedal adaptations, Australopithecus africanus retained some traits associated with arboreal, or tree-dwelling, locomotion. Its shoulder and hand bones, along with relatively long arms and slightly curved finger and toe bones, suggest that climbing was still a part of its lifestyle.
The cranial capacity of Australopithecus africanus was relatively small, ranging from approximately 400 to 500 cubic centimeters, which is comparable to that of a modern adult chimpanzee and about one-third the size of a modern human brain. The skull also featured a rounder cranium and a smaller brow ridge compared to earlier species like Australopithecus afarensis. The face was somewhat sloping and jutted out from beneath the braincase, with a pronounced jaw.
Dental features of Australopithecus africanus show a shift from ape-like dentition. The canine and incisor teeth were shorter and smaller than those found in apes, and a gap (diastema) between the canines and adjacent teeth was rare. However, the premolar and molar teeth were quite large and had thick enamel, suggesting a diet that included tough foods. Males of the species may have had more robust skulls than females. In terms of overall body size, males averaged around 140 cm (4 feet 7 inches) tall and weighed approximately 40 kg (88 pounds), while females were about 125 cm (4 feet 1 inch) tall and weighed around 30 kg (66 pounds).
Life in the Ancient Landscape
Australopithecus africanus inhabited a varied environment in South Africa, characterized by a mosaic of woodlands and savanna grasslands. This suggests an adaptation to both forested and more open habitats. The climate underwent changes over time, with savanna grasslands becoming more widespread after 2.5 million years ago as the environment grew drier.
The diet of Australopithecus africanus was likely omnivorous and diverse, a conclusion drawn from analyses of dental wear patterns and isotopic studies. While it primarily consumed fruits and leaves, stable carbon isotope analysis of their teeth indicates they also ate significant quantities of foods found in open environments, such as grasses, sedges, or animals that consumed these plants. Some evidence indicates the inclusion of meat, likely scavenged rather than hunted, though not in substantial amounts. The rapid maturation rate observed in Australopithecus africanus, similar to other apes, suggests a shorter child-rearing period compared to humans.
A Branch on the Human Family Tree
The placement of Australopithecus africanus within the broader human evolutionary tree has been a subject of ongoing scientific discussion. While it was once considered a direct ancestor of modern humans, new fossil discoveries have led many scientists to propose that it may represent an extinct side branch. However, there is still disagreement regarding its exact relationship to other species within the hominin lineage.
One perspective suggests that Australopithecus afarensis, known from East Africa, was the common ancestor of both Australopithecus africanus and the Homo lineage. This hypothesis is supported by the earlier dating of Au. afarensis fossils, some as old as 3.2 to 3.9 million years. However, some researchers maintain that Australopithecus africanus was indeed ancestral to the Homo genus, particularly to Homo habilis. The discovery of Australopithecus sediba in South Africa, which shares many characteristics with the Homo genus and is closely related to Au. africanus, has further fueled this debate.
The transitional features of Australopithecus africanus provide insights into the evolution of bipedalism and brain development. The species represents a stage where hominins developed efficient two-legged locomotion while still retaining some adaptations for climbing. The continuous discovery and re-evaluation of fossils continue to refine our understanding of Australopithecus africanus’s precise position in the human family tree.