Australopithecus africanus

Australopithecus africanus was an early hominid, an australopithecine, who lived between 2-3 million years ago in the Pliocene. In common with the older Australopithecus afarensis, A. africanus was slenderly built, or gracile, and was thought to have been a direct ancestor of modern humans. Fossil remains indicate that A. africanus was significantly more like modern humans than A. afarensis, with a more human-like cranium permitting a larger brain and more humanoid facial features. A. africanus has been found at only four sites in southern Africa - Taung (1924), Sterkfontein (1935), Makapansgat (1948) and Gladysvale (1992).

Famous fossils

Taung child

Raymond Dart became interested in fossils found at the lime mine at Taung near Kimberley, South Africa in 1924. The most promising of these was a skull of an odd ape-creature sharing human traits such as eye orbits, teeth, and, most importantly, the hole at the base of the skull over the spinal column (the foramen magnum) indicating a human-like posture. Dart assigned the specimen the name Australopithecus africanus ("southern ape of Africa").

This was the first time the word Australopithecus was assigned to any hominid. Dart claimed that the skull must have been an intermediate species between ape and humans, but his claim about the Taung Child was rejected by the scientific community at the time due to the belief that a large cranial capacity must precede bipedal locomotion. This was exacerbated by the widespread acceptance of the Piltdown Man. Sir Arthur Keith, a fellow anatomist and anthropologist, suggested that the skull belonged to a young ape, most likely from an infant gorilla. It was not until 20 years later that the public accepted the new genus and that australopithecines were a true member of Homininae.

Mrs. Ples

Dart's theory was supported by Robert Broom. In 1938 Broom classified an adult endocranial cast having a brain capacity of 485 cc, which had been found by G. W. Barlow, as Plesianthropus transvaalensis. On April 18, 1947, Broom and John T. Robinson discovered a skull belonging to a middle-aged female, (catalogue number STS 5), while blasting at Sterkfontein. Broom classified it also as Plesianthropus transvaalensis, and it was dubbed Mrs. Ples by Broom's young coworkers (though the skull is now thought to have belonged to a young male). The lack of facial projection in comparison to apes was noted by Raymond Dart (including from Taung Child), a trait in common with more advanced hominines. Both fossils were later classified as Australopithecus africanus.

Morphology and interpretations

Like Au. afarensis, Au. africanus the South African counterpart was generally similar in many traits, a bipedal hominid with arms slightly larger than the legs (a physical trait also found in chimpanzees). Despite its slightly more human-like cranial features, seen for example in the crania Mrs. Ples and STS 71, other more primitive features including ape-like curved fingers for tree climbing are also present.

Due to other more primitive features visible on Au. africanus, some researchers believe the hominin, instead of being a direct ancestor of more modern hominins, evolved into Paranthropus. One robust australopithecine seen as a descendent of Au. africanus is Paranthropus robustus. Both P. robustus and Au. africanus crania seem very alike despite the more heavily built features of P. robustus that are adaptations for heavy chewing like a gorilla. Au. africanus, on the other hand, had a cranium which quite closely resembled that of a chimp, yet both their brains measure about 400 cc to 500 cc and probably had an ape-like intelligence. Au. africanus had a pelvis that was built for slightly better bipedalism than that of Au. afarensis.

Sexual dimorphism

Recent evidence regarding modern human sexual dimorphism (physical differences between men and women) in the lumbar spine has been seen in pre-modern primates such as Au. africanus. This dimorphism has been seen as an evolutionary adaptation of females to better bear lumbar load during pregnancy, an adaptation that non-bipedal primates would not need to make.

A 2011 study using ratios of strontium isotopes in teeth suggested that Au. africanus and Paranthropus robustus groups in southern Africa were patrilocal: women tended to settle farther from their region of birth than men did.

External links

• MNSU
• Smithsonian
• Handprint
• Maropeng - The Cradle of Humankind Official Website
• UNESCO - Fossil Hominid Sites of Sterkfontein, Swartkrans, Kromdraai, and Environs