Australopithecus africanus

Australopithecus africanus
Temporal range: 3.3–2.1 Ma
Australopithecus africanus face2 (University of Zurich).JPG
Skull at the University of Zurich
Scientific classification edit
A. africanus
Binomial name
Australopithecus africanus
Dart, 1925 [1]

Australopithecus africanus is an extinct species of australopithecine, the first species to be described. In common with the older Australopithecus afarensis, A. africanus was of slender build, 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.[2] A. africanus has been found only in southern Africa at four sites: Taung (1924), Sterkfontein (1935), Makapansgat (1948) and Gladysvale (1992).[1]

In January 2019, scientists reported that Australopithecus sediba is distinct from, but shares anatomical similarities to, both the older Australopithecus africanus, and the younger Homo habilis.[3]

Famous fossils

Taung Child

Cast of the Taung Child.

Raymond Dart, then the head of the department of anatomy at the University of the Witwatersrand in Johannesburg, South Africa, became interested in fossils found at a limestone quarry at Taung near Kimberley, South Africa in 1924.[4][5] The most promising of these was a skull of an odd ape-like creature presenting human traits at the eye orbits, teeth, and, most importantly, the hole at the base of the skull over the spinal column (the foramen magnum); its placement indicated a human-like upright posture and implied a high probability that this hominid-to-hominin primate had achieved bipedal, as opposed to quadrupedal locomotion. Dart assigned the specimen the name Australopithecus africanus ("southern ape of Africa");[1] it was also dubbed "the Taung child".

This was the first time the word "ape" (-pithecus) was formally assigned to any hominin, which, in effect, formally declared humans as descended from apes. Dart theorized the Taung child skull must represent an intermediate species between apes and humans. But his claim was rejected by the scientific community, generally in deference to the broadly-held idea (idée fixe) that the early development of the line to humans required that a large cranium ("big brain") would precede bipedal locomotion; (see below, Mrs. Ples: cranial capacity).[1] And the rejection was buttressed by the widespread belief then, especially in British academia, that the Piltdown Man recently found in England was the likely progenitor of the human lineage. (Piltdown man was later exposed as a forgery.)

Sir Arthur Keith was an anatomist and anthropologist fellow in 1924, and a scientist whose personal prejudice looked to Europe—not to Asia or Africa—as the place where the early hominins would be shown to have emerged.[6] He dismissed Dart's claim, suggesting instead that the Taung child skull belonged to a young ape, most likely an infant gorilla or chimpanzee.[7][8] Keith's persistence in denouncing the possibility of Australopithecus while justifying the plausibility of Piltdown man was instrumental in binding the two issues inextricably together for over a generation.

Keith immersed himself in defending the Piltdown man and his reputation suffered greatly after the hoax was exposed in 1953. Phillip Tobias, in a lengthy essay published in Current Anthropology in 1992, detailed the history of the investigation of the hoax. He presented argument that implicated the motive of Keith's adamant and continual opposition to Australopithecus, to wit: if Australopithecus was a hominin ancestor, then Piltdown man could not have been and its bona fides would have been suspect and called out for formal investigation. As part of the essay Tobias debated the inconsistencies in Keith's statements and actions with contemporary members of the science community.[9]

Keith's persistent animus towards the Taung child discovery caused serious consequences; from Dart's announcement in 1924, it took nearly 30 years before the methods of science revealed the Piltdown man hoax and supported the validity of the claims (of hominin status) for Australopithecus.

Mrs. Ples

Skull of "Mrs. Ples", Australopithecus africanus; Transvaal Museum Pretoria.

Dart's theory—that the skull known as the Taung child was a human ancestor—was supported by Robert Broom, a paleontologist with the Transvaal Museum of natural history in Pretoria.[10] In 1936, the Sterkfontein caves yielded the first adult australopithecine, substantially strengthening Dart's claim for Broom. Later, Broom classified an adult endocranial cast having a brain capacity of 485 cc (found by G. W. Barlow) as Plesianthropus transvaalensis (near-man from Transvaal). In April 1947, while blasting at Sterkfontein, he and John T. Robinson discovered a skull belonging to a middle-aged female[11] (catalogue number STS 5) which he also classified as Plesianthropus transvaalensis (it was dubbed "Mrs. Ples" by Broom's young coworkers although the skull is now thought to have belonged to a young male). Both fossils were later classified as Australopithecus africanus.

Mrs. Ples, whose cranial capacity is only about 485 cubic centimetres (cc), was one of the first fossils to reveal that upright walking (bipedal locomotion) had evolved well before any significant growth in brain size.[12] And, in comparison to modern apes, Dart noted as with the Taung child the lack of facial (prognathous) projection, a characteristic shared with advanced hominines.

Little Foot

In 1997, paleoanthropologist Ronald J. Clarke began extracting the remains of a near-complete skeleton of Australopithecus named Little Foot (StW 573), which was previously discovered in the cave system at Sterkfontein; extraction or preparation and analysis of the specimen has been nearing completion in 2018.[13] Little Foot is currently classified as (lumped into) Australopithecus africanus; Clarke suggests that Little Foot doesn't belong to either species afarensis or africanus, but to a unique Australopithecus species found at Makapansgat and Sterkfontein (and named Australopithecus prometheus by Raymond Dart).[14][15] Analysis made in 2015 by a new radioisotopic technique dated the Little Foot specimen to about 3.7 mya.[16]