Australopithecus africanus

Australopithecus africanus ("southern ape of Africa") lived in southern Africa between approximately 3.7 and 2.1 million years ago.¹ It was the first australopithecine ever discovered, identified by Raymond Dart in 1924 from a juvenile skull found at a limestone quarry near Taung, South Africa.² Its discovery provided the earliest fossil evidence supporting Darwin's 1871 prediction that humans originated in Africa, and its eventual acceptance overturned decades of Eurocentric assumptions about human origins.^{3, 4}

The Taung Child

In late 1924, quarry workers near the village of Taung in what is now South Africa's North West Province blasted loose a block of limestone breccia containing a small fossilized skull.² The quarry manager forwarded it to Raymond Dart, a young anatomy professor at the University of the Witwatersrand.⁵ Dart received the specimen on 28 November 1924 and immediately recognized features distinguishing it from any known ape: the foramen magnum was positioned forward beneath the cranium rather than toward the back, suggesting upright walking.^{2, 6}

After just five weeks of preparation, Dart published his analysis in the 7 February 1925 issue of Nature.² He named the new species Australopithecus africanus and argued it was intermediate between apes and humans. The skull belonged to a child of about three to four years, with deciduous teeth and the first permanent molars beginning to erupt.^{2, 7} Cranial capacity was approximately 405 cc (estimated adult size ~440 cc)—larger than a chimpanzee of comparable age but far smaller than a modern human.⁸ A natural endocast preserved within the skull showed what Dart interpreted as an expanded occipital association cortex, a region involved in higher visual processing.^{2, 9}

Decades of rejection

The scientific establishment's response was swift and largely negative. In the next issue of Nature, four leading British anatomists published critical responses. Three—Arthur Keith, Grafton Elliot Smith, and Arthur Smith Woodward—sat on the committee that had authenticated Piltdown Man, a supposed fossil hominin "discovered" in England in 1912 that would not be exposed as a forgery until 1953.^{10, 11} Keith dismissed the Taung specimen as a young ape; Woodward insisted it could not be placed on the human family tree.^{5, 12}

Several factors conspired against Dart. Piltdown had created the expectation that human ancestors should have large brains and ape-like jaws—the precise opposite of what A. africanus displayed.^{10, 13} A deep-seated assumption placed the cradle of humanity in Asia or Europe, not Africa, and the idea of an African genesis struck many as implausible or offensive to prevailing racial prejudices.^{3, 14} The Taung specimen's juvenile status made it easy for skeptics to argue its human traits were merely those of an immature ape.⁵

Deeply affected by the rejection, Dart largely withdrew from paleoanthropology for nearly two decades, leaving the defense of Australopithecus to a crucial ally: the Scottish-born South African paleontologist Robert Broom.¹⁵

Broom's vindication and Sterkfontein

Robert Broom, already sixty-nine and an established authority on mammal-like reptiles, took up the search with extraordinary energy. In August 1936, the quarry manager at Sterkfontein handed Broom an adult hominin endocast from the cave's breccia. Within days Broom recovered the associated cranium—the first adult specimen of a South African australopithecine.^{15, 16} He later recovered additional material from Sterkfontein and from Kromdraai, where he identified the robust australopithecine Paranthropus robustus in 1938.¹⁷

The Sterkfontein caves, about 40 km northwest of Johannesburg in the Cradle of Humankind UNESCO World Heritage Site (inscribed 1999), have yielded more than 500 hominin specimens.^{18, 19} Dolomitic limestone created natural traps: animals and hominins fell through surface openings, and their bones became cemented in breccia. Member 4 (~2.6–2.0 Ma) produced the bulk of the A. africanus material, while the deeper Member 2 preserves the older StW 573 skeleton.^{1, 20}

Broom's most celebrated find came on 18 April 1947: a remarkably complete adult cranium from Member 4, initially assigned to Plesianthropus transvaalensis and popularly known as "Mrs. Ples" (though the specimen may actually be male).^{21, 22} Its small canines, rounded cranium, and forward-positioned foramen magnum made it far harder to dismiss the australopithecines as mere apes.¹⁵

The turning point came that same year. Arthur Keith, perhaps Dart's most prominent critic, published a remarkable recantation: "Professor Dart was right and I was wrong."^{12, 15} The final blow fell in 1953, when Oakley, Weiner, and Le Gros Clark exposed Piltdown Man as a deliberate forgery—a modern human cranium paired with a chemically treated orangutan jaw.¹⁰ With Piltdown discredited, the small-brained, bipedal pattern exemplified by A. africanus was recognized as the true sequence: upright walking preceded brain enlargement.¹³

Anatomy and morphology

A. africanus stood approximately 1.1–1.4 m tall, with an estimated body mass of 30–41 kg and moderate sexual dimorphism.^{1, 23} The cranium was rounded and gracile, lacking the sagittal crests and flared cheekbones of Paranthropus. Cranial capacities ranged from ~400 to 560 cc (mean ~460 cc)—roughly a third of a modern human brain but larger than a chimpanzee of similar body mass.^{8, 24}

Cranial capacity of key A. africanus specimens (cc)^{8, 24, 25}

The canines are reduced relative to great apes, and the premolars and molars are enlarged with thick enamel—adaptations to hard or tough foods such as seeds, nuts, and tubers.^{1, 26} Microwear and stable isotope studies show A. africanus consumed a broader diet than A. afarensis, including significant C4 resources (grasses, sedges, or animals that ate them), indicating adaptation to more open environments alongside woodland.²⁷

Multiple features confirm bipedal locomotion. The forward foramen magnum, first recognized by Dart, indicates the head was balanced atop an upright spine.^{2, 6} The pelvis (best known from Sts 14) is broad and short, with a well-developed attachment for the rectus femoris muscle used in upright walking.²³ The femur's valgus angle positions the knee under the body's center of gravity—a hallmark of bipeds.¹ Yet curved finger bones and a cranially oriented shoulder socket indicate A. africanus retained significant climbing ability alongside terrestrial bipedalism.^{23, 28}

Little Foot

The story of StW 573, universally known as "Little Foot," is one of the most remarkable in fossil discovery. In 1994, Ron Clarke of the University of the Witwatersrand was sorting through boxes of animal fossils collected from Sterkfontein's Silberberg Grotto in the late 1970s. Among them he identified four articulating hominin foot bones with a mix of ape-like and human-like features.²⁹ Clarke and Phillip Tobias announced the find in 1995, and the bones' clean breaks suggested the rest of the skeleton might still lie in the cave breccia.^{29, 30}

In 1997, Clarke sent assistants Stephen Motsumi and Nkwane Molefe into the Silberberg Grotto with casts of the broken surfaces. Working by handheld lamp, they located a matching tibia cross-section protruding from the cave wall within two days.^{30, 31} What followed was one of the longest excavations in the field's history. Embedded in extremely hard breccia, the skeleton was extracted by hand with air scribes and chisels over more than twenty years, not fully prepared until 2017.^{30, 31}

The result: approximately 90% of the skeleton recovered—the most complete Australopithecus ever found.²⁵ The individual was probably an adult female, ~1.3 m tall, with a cranial capacity of ~408 cc, small even by australopithecine standards.^{25, 32} Cosmogenic nuclide burial dating yielded an age of 3.67 million years, making Little Foot contemporaneous with A. afarensis in East Africa and significantly older than most A. africanus material from Member 4.^{33, 34}

The A. prometheus debate

The taxonomic assignment of Little Foot is one of the most contested questions in current paleoanthropology. Clarke has argued StW 573 belongs not to A. africanus but to a separate species, Australopithecus prometheus—a name Dart coined in 1948 for Makapansgat specimens, later subsumed into A. africanus by most researchers.^{25, 35}

Clarke and Kuman's 2019 description laid out the morphological case: StW 573 has a flatter, more prognathic face; a more ape-like dental arcade; extremely heavy anterior dental wear resembling A. anamensis; and distinctive cranial vault proportions.²⁵ Clarke grouped additional Sterkfontein and Makapansgat specimens with StW 573 as A. prometheus, proposing that two gracile australopithecine species coexisted in South Africa.^{25, 35}

Many researchers counter that the variation Clarke attributes to species-level differences falls within the range expected for a single sexually dimorphic species.^{22, 36} A 2025 quantitative analysis by Martin and colleagues concluded StW 573 does not fall outside the morphometric range of A. africanus.³⁶ The debate remains unresolved, but its outcome has important implications for australopithecine diversity and the lineage leading to Homo.³⁵

Key specimens

Major Australopithecus africanus specimens^{2, 21, 25}

The Taung Child remains the holotype. Despite its juvenile status, it preserves critical diagnostic features: forward foramen magnum, small erupting canines, a parabolic dental arcade, and the natural endocast Dart used to argue for expanded association cortices.^{2, 9} Taung has not yielded additional hominin material.⁷

Sts 5 ("Mrs. Ples") is the most iconic adult specimen. The near-complete cranium, lacking only the lower jaw and some teeth, has served as the basis for countless studies; CT analysis revised its endocranial volume to ~485 cc.^{8, 21} Despite the nickname, several researchers now argue the specimen is male.²²

Little Foot's completeness has provided unprecedented postcranial information. The skeleton includes a complete arm and hand, both legs and feet, much of the vertebral column, ribs, pelvis, and skull with dentition.^{25, 32} Relatively long arms and short legs indicate a locomotor repertoire combining bipedalism with significant climbing.³² The hand shows curved phalanges for branch-grasping, while the foot displays a divergent big toe with grasping capacity, unlike the fully adducted hallux of modern humans.²⁹

Evolutionary significance

A. africanus has long been considered a plausible ancestor or close relative of Homo. In many phylogenetic analyses it occupies a position between A. afarensis and the earliest Homo (~2.8–2.3 Ma).^{1, 37} Its mix of primitive features (small brain, arboreal limb proportions) and derived ones (reduced canines, thick enamel, committed bipedalism) exemplifies mosaic evolution, where different anatomical systems change at different rates.²³

In southern Africa, A. africanus overlapped temporally with Paranthropus robustus and possibly early Homo.^{1, 17} If Clarke's revision is accepted and Little Foot represents A. prometheus, then australopithecine diversity was even greater, with at least two gracile species present before the emergence of Paranthropus and Homo.^{25, 35}

The broader significance of A. africanus extends beyond taxonomy. It was this species that first demonstrated a fundamental principle: bipedalism preceded brain enlargement. Dart's insight, ridiculed in 1925, is now one of the most firmly established facts in paleoanthropology. The australopithecines walked upright for millions of years before the larger-brained Homo appeared, overturning the Victorian expectation that a large brain was the first step to becoming human.^{2, 13} The century-long arc from Dart's discovery to Clarke's meticulous excavation of Little Foot illustrates how South African fossils have repeatedly reshaped our understanding of human origins.³⁸