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''Australopithecus africanus'' is an
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
of
australopithecine Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally ''Australopithecus'' ( cladistically including the genera ''Homo'', '' Paranthropus'', and ''Kenyanthropus''), and it typically inclu ...
which lived between about 3.3 and 2.1 million years ago in the
Late Pliocene Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effe ...
to
Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
of
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
. The species has been recovered from Taung, Sterkfontein, Makapansgat, and Gladysvale. The first specimen, the
Taung child The Taung Child (or Taung Baby) is the fossilised skull of a young '' Australopithecus africanus''. It was discovered in 1924 by quarrymen working for the Northern Lime Company in Taung, South Africa. Raymond Dart described it as a new specie ...
, was described by anatomist Raymond Dart in 1924, and was the first early
hominin The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos) and in standard usage excludes the genus ''Gorilla'' (gorillas). The ...
found. However, its closer relations to humans than to other apes would not become widely accepted until the middle of the century because most had believed humans evolved outside of Africa. It is unclear how ''A. africanus'' relates to other hominins, being variously placed as ancestral to ''
Homo ''Homo'' () is the genus that emerged in the (otherwise extinct) genus '' Australopithecus'' that encompasses the extant species ''Homo sapiens'' ( modern humans), plus several extinct species classified as either ancestral to or closely rela ...
'' and '' Paranthropus'', to just ''Paranthropus'', or to just '' P. robustus''. The specimen " Little Foot" is the most completely preserved early hominin, with 90% of the skeleton intact, and the oldest South African australopith. However, it is controversially suggested that it and similar specimens be split off into "''A. prometheus''". ''A. africanus'' brain volume was about . Like other early hominins, the
cheek teeth Cheek teeth or post-canines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and p ...
were enlarged and had thick enamel. Male skulls may have been more robust than female skulls. Males may have been on average in height and in weight, and females and . ''A. africanus'' was a competent biped, albeit less efficient at walking than humans. ''A. africanus'' also had several upper body traits in common with arboreal non-human apes. This is variously interpreted as either evidence of a partially or fully arboreal lifestyle, or as a non-functional vestige from a more apelike ancestor. The upper body of ''A. africanus'' is more apelike than that of the East African ''
A. afarensis ''Australopithecus afarensis'' is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would not ta ...
''. ''A. africanus'', unlike most other primates, seems to have exploited C4 foods such as grasses, seeds, rhizomes, underground
storage organ A storage organ is a part of a plant specifically modified for storage of energy (generally in the form of carbohydrates) or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have ...
s, or potentially creatures higher up on the food chain. Nonetheless, the species had a highly variable diet, making it a generalist. It may have eaten lower quality, harder foods, such as nuts, in leaner times. To survive, children may have needed nursing during such periods until reaching perhaps 4 to 5 years of age. The species appears to have been patrifocal, with females more likely to leave the group than males. ''A. africanus'' lived in a gallery forest surrounded by more open grasslands or bushlands. South African australopithecine remains probably accumulated in caves due to predation by large carnivores (namely big cats), and the Taung child appears to have been killed by a bird of prey. ''A. africanus'' probably went extinct due to major climatic variability and volatility and possibly competition with ''Homo'' and ''P. robustus''.


Research history

In 1924, Australian anatomist Professor Raymond Dart, since 1923 working in South-Africa, was informed by one of his students, Josephine Salmons, that monkey fossils (of '' Papio izodi'') had been discovered by shotfirer M.G. de Bruyn in a
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
quarry in Taung, South Africa, operated by the Northern Lime Company. Knowing that Scottish geologist Professor Robert Burns Young was at the time carrying out excavations in the area in search of archaic human remains like '' Homo rhodesiensis'' from Kabwe, Zambia (at the time Broken Hill, Northern Rhodesia) discovered in 1921, he asked his colleague to send him some primate remains from the quarry. On 24 November 1924, Dart received two boxes with fossils collected by De Bruyn. In them, he noticed a natural brain endocast and a face of a, now known to be 2.8 million year old, juvenile skull, the
Taung child The Taung Child (or Taung Baby) is the fossilised skull of a young '' Australopithecus africanus''. It was discovered in 1924 by quarrymen working for the Northern Lime Company in Taung, South Africa. Raymond Dart described it as a new specie ...
, that he immediately recognised as a transitional fossil between apes and humans. Most notably, it had a small brain size yet was, as shown by the position of the '' foramen magnum'', bipedal. Dart, after hastily freeing the fossil from its matrix, already in January 1925 named the specimen as a new genus and species: ''Australopithecus africanus''. At this time, great apes were classified into the
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Pongidae encompassing all non-human fossil apes, and
Hominidae The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the ...
encompassing humans and ancestors. Dart felt the Taung child fit into neither, and erected the family "Homo-simiadæ" ("man-apes"). This family name was soon abandoned, and Dart proposed "Australopithecidae" in 1929. In 1933, South African palaeoanthropologist
Robert Broom Robert Broom FRS FRSE (30 November 1866 6 April 1951) was a British- South African doctor and palaeontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University of Glasgow. From 1903 to 1910, he ...
suggested moving ''A. africanus'' into Hominidae, which at the time contained only humans and their ancestors. ''A. africanus'' was the first evidence that humans evolved in Africa, as
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended ...
had postulated in his 1871 '' The Descent of Man''. However, Dart's claim of the Taung child as the transitional stage between apes and humans was at odds with the-then popular model of human evolution which held that large brain size and humanlike characteristics had developed rather early on, and that large brain size evolved before bipedalism. Resultantly, ''A. africanus'' was generally cast aside as a member of the
gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four ...
or
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative t ...
lineages, most notably by Sir Arthur Keith. This view was perpetuated by
Charles Dawson Charles Dawson (11 July 1864 – 10 August 1916) was a British amateur archaeologist who claimed to have made a number of archaeological and palaeontological discoveries that were later exposed as frauds. These forgeries included the Piltdown ...
's 1912 hoax
Piltdown Man The Piltdown Man was a paleoanthropological fraud in which bone fragments were presented as the fossilised remains of a previously unknown early human. Although there were doubts about its authenticity virtually from the beginning, the remains ...
hailing from Britain. Further, the discovery of the humanlike Peking Man (''Homo erectus pekinensis'') in China also seemed to place the origins of humankind outside of Africa. Humanlike characteristics of the Taung child were attributed to the specimen's juvenile status, meaning they would disappear with maturity. Nonetheless, Dart and Broom continued to argue that ''Australopithecus'' was far removed from chimpanzees, showing several physical and claiming some behavioural similarities with humans. To this extent, Dart made note of the amalgamations of large mammal bone fragments in australopithecine-bearing caves which are now attributed to
hyena Hyenas, or hyaenas (from Ancient Greek , ), are feliform carnivoran mammals of the family Hyaenidae . With only four extant species (each in its own genus), it is the fifth-smallest family in the Carnivora and one of the smallest in the cl ...
activity. However, Dart proposed that the bones were instead evidence of what he named the " osteodontokeratic culture" produced by australopithecine hunters, who manufactured weapons using the long bones, teeth, and horns of large hoofed prey: Broom was one of the few scientists defending the close human affinities of ''Australopithecus africanus''. In 1936, he was informed by two of Dart's students, Trevor R. Jones and G. Schepers, that human-like remains had been discovered in the Sterkfontein Cave quarries. On 9 August 1936, he asked G.W. Barlow to provide him with any finds. On 17 August 1936 he received an adult skull including a natural endocast, specimen Sts 60. However, Broom classified it as a new species, "''A. transvaalensis''", and in 1938 moved it into a new genus as "''Plesianthropus transvaalensis''". He also discovered the robust australopithecine ''
Paranthropus robustus ''Paranthropus robustus'' is a species of robust australopithecine from the Early and possibly Middle Pleistocene of the Cradle of Humankind, South Africa, about 2.27 to 0.87 (or, more conservatively, 2 to 1) million years ago. It has been iden ...
'', showing evidence of a wide diversity of
Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
"man-apes". Before
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
, several more sites bore ''A. africanus'' fossils. A detailed monograph by Broom and palaeoanthropologist Gerrit Willem Hendrik Schepers in 1946 regarding these australopithecines from South Africa, as well as several papers by British palaeoanthropologist Sir Wilfrid Le Gros Clark, had turned around scientific opinion, garnering wide support for ''A. africanus'' classification as a human ancestor. In 1947, the most complete skull was discovered, STS 5 (" Mrs. Ples"). Wider acceptance of ''A. africanus'' prompted re-evaluation of Piltdown Man in 1953, revealing its falsehood. In 1949, Dart recommended splitting a presumed-female facial fragment from Makapansgat, South Africa, (MLD 2) into a new species as "''A. prometheus''". In 1954, he referred another presumed-female specimen from Makapansgat (a jawbone fragment). However, in 1953, South African palaeontologist
John Talbot Robinson John Talbot Robinson FRSSAf (10 January 1923 – 12 October 2001) was a distinguished South African hominin paleontologist. His most famous discovery (with Robert Broom) was the nearly complete fossil skull of the hominin species ''Australop ...
believed that splitting species and genera on such fine hairs was unjustified, and that australopithecine remains from East Africa recovered over the previous couple of decades were indistinguishable from "''Plesianthropus''"/''A. africanus''. Based on this, in 1955, Dart agreed with synonymising "''A. prometheus''" with ''A. africanus'' because they are already quite similar to each other, and if speciation did not occur across a continent, then it quite unlikely occurred over a couple tens of kilometres according to Dart. The East African remains would be split off into ''
A. afarensis ''Australopithecus afarensis'' is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would not ta ...
'' in 1978. In 2008, palaeoanthropologist
Ronald J. Clarke Ronald John Clarke is a paleoanthropologist most notable for the discovery of "Little Foot", an extraordinarily complete skeleton of ''Australopithecus'', in the Sterkfontein Caves. A more technical description of various aspects of his descri ...
recommended reviving "''A. prometheus''" to house the StW 573 nearly-complete skeleton (" Little Foot"), StS 71 cranium, StW 505 cranium, StW 183
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
, StW 498 maxilla and jawbone, StW 384 jawbone, StS 1 palate, and MLD 2. In 2018, palaeoanthropologists Lee Rogers Berger and John D. Hawks considered "''A. prometheus''" a '' nomen nudum'' ("naked name"), and has not been properly described with diagnostic characteristics which separate it from ''A. africanus''. At the time, these remains were dated to 3.3 million years ago in the
Late Pliocene Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effe ...
. In 2019, Clarke and South African palaeoanthropologist Kathleen Kuman redated StW 573 to 3.67 million years ago, making it the oldest ''Australopithecus'' specimen from South Africa. They considered its antiquity further evidence of species distinction, drawing parallels with '' A. anamensis'' and ''A. afarensis'' from Middle Pliocene East Africa. Little foot is the most complete early hominin skeleton ever recovered, with about 90% preserved. In addition to Taung, Sterkfontein, and Makapansgat, ''A. africanus'' was in 1992 discovered in Gladysvale Cave. The latter three are in the
Cradle of Humankind The Cradle of Humankind is a paleoanthropological site and is located about northwest of Johannesburg, South Africa, in the Gauteng province. Declared a World Heritage Site by UNESCO in 1999, the site is home to the largest concentration of h ...
. Many hominin specimens traditionally assigned to ''A. africanus'' have been recovered from Sterkfontein Member 4 (including Mrs. Ples and 2 partial skeletons), previously dated to 2.8 to 2.15 million years ago. But in 2022 a team including Clarke and Kuman used cosmogenic nuclide techniques to date Member 4 at 3.4 million years, which it says discredits the assumption that ''A. africanus'' descended from ''A. afarensis''. However, given the wide range of variation exhibited by these specimens, it is debated if all these elements can be confidently assigned to only ''A. africanus''. At present, the classification of australopithecines is in disarray. ''Australopithecus'' is considered a grade taxon, whose members are united by their similar physiology rather than close relations with each other over other hominin genera. It is unclear how ''A. africanus'' relates to other hominins. The discovery of
Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
''Homo'' in Africa during the latter half of the 20th century placed humanity's origins on the continent and ''A. africanus'' as ancestral to ''Homo''. The discovery of ''A. afarensis'' in 1978, at the time the oldest known hominin, prompted a hypothesis that ''A. africanus'' was ancestral to ''P. robustus'', and ''A. afarensis'' was the last common ancestor between ''Homo'' and ''A. africanus''/''P. robustus''. It is also suggested that ''A. africanus'' is closely related to ''P. robustus'' but not to the other '' Paranthropus'' species in East Africa, or that ''A. africanus'' is ancestral to all ''Paranthropus''. ''A. africanus'' has also been postulated to have been ancestral to '' A. sediba'' which also inhabited the Cradle of Humankind, perhaps contemporaneously. ''A. sediba'' is also postulated to have been ancestral to ''Homo'', which if correct would indeed put ''A. africanus'' in an ancestral position to ''Homo''.


Anatomy


Skull

Based on 4 specimens, the ''A. africanus'' brain volume averaged about . Based on this, neonatal brain size was estimated to have been using trends seen in adult and neonate brain size in modern primates. If correct, this would indicate that ''A. africanus'' was born with about 38% of its total brain size, which is more similar to non-human great apes at 40% than humans at 30%. The
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in th ...
has wide semicircular canals like non-human apes, as well as loose turns at the terminal end of the
cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory o ...
like humans. Such a mix may reflect habitual locomotion both in the trees and walking while upright because inner ear anatomy affects the vestibular system (sense of balance). ''A. africanus'' had a
prognathic Prognathism, also called Habsburg jaw or Habsburgs' jaw primarily in the context of its prevalence amongst members of the House of Habsburg, is a positional relationship of the mandible or maxilla to the skeletal base where either of the jaws pr ...
jaw (it jutted out), a somewhat dished face (the cheek were inflated, causing the nose to be at the bottom of a dip), and a defined brow ridge. The temporal lines running across either side of the braincase are raised as small crests. The canines are reduced in size compared to non-human apes, though still notably bigger than those of modern humans. Like other early hominins, the
cheek teeth Cheek teeth or post-canines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and p ...
are large and feature thick enamel. In the upper jaw the third molar is the largest molar, and in the lower jaw it is the second molar. ''A. africanus'' had a fast, apelike dental development rate. According to Clarke, the older "''A. prometheus''" is distinguished by larger and more bulbous cheek teeth, larger incisors and canines, more projecting cheeks, more widely spaced
eye socket In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is , of ...
s, and a
sagittal crest A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exception ...
. ''A. africanus'' has a wide range of variation for skull features, which is typically attributed to moderate to high levels of
sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
in that males were more robust than females.


Build

In 1992, American anthropologist
Henry McHenry Henry Malcolm McHenry (born May 19, 1944) is a professor of anthropology at the University of California, Davis, specializing in studies of human evolution, the origins of bipedality, and paleoanthropology. McHenry has published on the comparative ...
estimated an average weight (when assuming humanlike or apelike body proportions, respectively) of for males based on five partial leg specimens, and for females based on seven specimens. In 2015, American anthropologist
William L. Jungers William L. Jungers (born November 17, 1948) is an American anthropologist, Distinguished Teaching Professor and the Chair of the Department of Anatomical Sciences at State University of New York at Stony Brook on Long Island, New York. He is best ...
and colleagues similarly reported an average weight (without attempting to distinguish males from females) of with a range of for weight based on 19 specimens. Based on seven specimens, McHenry estimated that males, on average, grew to tall and females . In 2017, based on 24 specimens, anthropologist Manuel Will and colleagues estimated a height of with a range of . The elderly, probably female StW 573 was estimated to have stood about . Based on the ''A. afarensis'' skeleton DIK-1-1, australopiths are thought to have had a humanlike spine, with 7
neck vertebra In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sau ...
e, 12 thoracic vertebrae, and (based on other early australopith skeletons) 5 flexible lumbar vertebrae. In StW 573, the atlas bone in the neck, important for swiveling and stabilising the head, is more similar to non-human apes and indicates greater mobility to swivel up and down than in humans. Such motion is important for arboreal species to locate and focus on climbable surfaces. The StW 573 atlas shows similar mechanical advantages for the muscles which move the
shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists ...
as chimps and
gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four ...
s, which may indicate less lordosis (normal curvature of the spine) in ''A. africanus'' neck vertebrae. However, the later StW 679 has some similarities to human atlases, which could potentially indicate gradual evolution away from the ape condition. StW 573 has a narrow thoracic inlet unlike ''A. afarensis'' and humans. The
clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the r ...
is proportionally quite long, with a similar absolute length to that of modern humans. Like in modern women, L3–L5 curve outwards in specimen StS 14, whereas these are straighter in StW 431 as in modern men. This probably reflects reinforcement of the female spine to aid in walking upright while pregnant. The StS 14 partial skeleton preserves a rather complete
pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...
. Like in the restored pelvis of the Lucy specimen (''A. afarensis''), the sacrum was relatively flat and orientated more towards the back than in humans, and the pelvic cavity had an overall platypelloid shape. This could indicate a broad
birth canal In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the Vulval vestibule, vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucous membrane ...
compared to neonate head size, and thus a non-rotational birth (unlike humans), though this is debated. When standing, the angle between the sacrum and the lumbar vertebrae was reconstructed to have been about 148.7°, which is much more similar to that of chimps (154.6°) than humans (118.3°). This would indicate ''A. africanus'' standing posture was not as erect as in humans.


Limbs

The ''A. africanus'' hand and arm exhibit a mosaic anatomy, with some aspects more similar to humans and others to non-human apes. It is unclear if this means australopiths were still arboreal to a degree, or if these traits were simply inherited from the human–chimpanzee last common ancestor. Nonetheless, ''A. africanus'' exhibits a more ape-like upper limb anatomy than ''A. afarensis'', and is typically interpreted as having been, to some extent, arboreal. Like in arboreal primates, the fingers are curved, the arms relatively long and the shoulders are in a shrugging position. The ''A. africanus'' shoulder is most like that of
orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genu ...
s, and well suited for maintaining stability and bearing weight while raised and placed overhead. However, the right clavicle of StW 573 has a distinctly S-shaped (sigmoid) curve like humans, which indicates a humanlike moment arm for stabilising the
shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists ...
against the humerus. The ''A. africanus'' arm bones are consistent with powerful muscles useful in climbing. Nonetheless, the brachial index (the forearm to humerus ratio) is 82.8–86.2 (midway between chimpanzees and humans), which indicates a reduction in forearm length from the more ancient hominin '' Ardipithecus ramidus''. The thumb and wrist indicate humanlike functionality with a precision grip and forceful opposition between the thumb and fingers. The adoption of such a grip is typically interpreted as an adaptation for tool making at the expense of efficient climbing and arboreal habitation. The leg bones clearly show that ''A. africanus'' habitually engaged in bipedal locomotion, though some aspects of the
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...
e are apelike, which could indicate that the leg musculature had not been fully reorganised into the human condition. If correct, its functional implications are unclear. The trabecular bone at the hip joint is distinctly humanlike, which would be inconsistent with the great degrees of hip loading required in prolonged arboreal activity. The tibia met the foot at a similar angle as it does in humans, which is necessary for habitual bipedalism. Consequently, the ankle was not as adept for climbing activities as it is in non-human apes. However, the modern Congo Twa hunter–gatherers can achieve a chimp-like angle with the ankle while climbing trees due to the longer fibres in the gastrocnemius (calf) muscle instead of specific skeletal adaptations. Some aspects of the ankle bone were apelike which may have affected walking efficiency. The foot elements of ''A. africanus'' are largely known from remains from Sterkfontein Member 4. The foot is humanlike with a stiff midfoot and lack of a midtarsal break (which allows non-human apes to lift the heel independently from the rest of the foot). Though ''A. africanus'' had an
adducted Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
big toe (it was not dextrous) like humans, ''A. africanus'' likely did not push off with the big toe, using the side of the foot instead. StW 573 is the oldest hominin specimen with an adducted big toe. The specimen StW 355 is the most curved proximal foot phalanx bone of any known hominin, more similar to that of orangutans and siamangs. The arms of StW 573 were about , and her legs . This means the arm was 86.9% the length of the leg. She is the first and only early hominin specimen to definitively show that the arms were almost all long as the legs. Nonetheless, these proportion are more similar to humans than non-human apes, with
human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
s at 64.5–78%,
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative t ...
s about 100%,
gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four ...
s 100–125%, and
orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genu ...
s 135–150.9%.


Palaeobiology


Diet

In 1954, Robinson proposed that ''A. africanus'' was a generalist
omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...
whereas ''P. robustus'' was a specialised herbivore; and in 1981, American palaeoanthropologist Frederick E. Grine suggested that ''P. robustus'' specialised on hard foods such as nuts whereas ''A. africanus'' on softer foods such as fruits and leaves. Based on carbon isotope analyses, ''A. africanus'' had a highly variable diet which included a notable amount of C4 savanna plants such as grasses, seeds, rhizomes, underground
storage organ A storage organ is a part of a plant specifically modified for storage of energy (generally in the form of carbohydrates) or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have ...
s, or perhaps grass-eating invertebrates (such as locusts or
termite Termites are small insects that live in colonies and have distinct castes ( eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blat ...
s),
grazing In agriculture, grazing is a method of animal husbandry whereby domestic livestock are allowed outdoors to roam around and consume wild vegetations in order to convert the otherwise indigestible (by human gut) cellulose within grass and ot ...
mammals, or insectivores or carnivores. Most primates do not eat C4 plants. ''A. africanus'' facial anatomy seems to suggest adaptations for producing high stress on the premolars, useful for eating small, hard objects such as seeds and nuts that need to be cracked open by the teeth, or for processing a large quantity of food at one time. However, like for ''P. robustus'', microwear analysis on the cheek teeth indicate small, hard foods were infrequently eaten, probably as fall back foods during leaner times. Still, ''A. africanus'', like chimps, may have required
hammerstone In archaeology, a hammerstone is a hard cobble used to strike off lithic flakes from a lump of tool stone during the process of lithic reduction. The hammerstone is a rather universal stone tool which appeared early in most regions of the wor ...
s to crack open nuts (such as marula nuts), though ''A. africanus'' is not associated with any tools. ''A. africanus'' conspicuously lacks evidence of dental cavities, whereas ''P. robustus'' seems to have had a modern humanlike cavity rate; this could possibly indicate that ''A. africanus'' either did not often consume high-sugar cavity-causing foods—such as fruit, honey, and some nuts and seeds—or frequently consumed gritty foods which decrease cavity incidence rate. However, the 2nd right permanent incisor (STW 270) and right canine (STW 213) from the same individual show lesions consistent with acid erosion, which indicates this individual was regularly biting into acidic foods such as citrus. Tubers could have caused the same damage if some chewing was done by the front teeth.
Barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...
continually deposits onto ''A. africanus'' teeth until about 6–9 months of development, and then decreases until about 12 months. Because the barium was most likely sourced from breast milk, this probably reflects the weaning age. This is comparable to the human weaning age. Following this initial period, barium deposits stall and then restart cyclically every year for several years. In the first molar specimen StS 28 (from Sterkfontein), this occurred every 6–9 months, and in the lower canine specimen StS 51 every 4–6 months, and this carried on until 4–5 years of development.
Lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense soli ...
and
strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is e ...
also deposit cyclically. Cyclical barium, lithium, and strontium bands occur in modern primates—for example, wild orangutans up to 9 years of age—which is caused by seasonal famine when a child has to rely on nursing to sustain themselves and less desirable fallback foods. However, it is unclear if this can be extended to ''A. africanus''.


Society

The group dynamics of australopithecines is difficult to predict with any degree of accuracy. A 2011
strontium isotope The alkaline earth metal strontium (38Sr) has four stable, naturally occurring isotopes: 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.0%) and 88Sr (82.58%). Its standard atomic weight is 87.62(1). Only 87Sr is radiogenic; it is produced by decay from the ...
study of ''A. africanus'' teeth from the
dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...
Sterkfontein Valley found that, assuming that especially small teeth represented female specimens and especially large teeth males, females were more likely to leave their place of birth ( patrilocal). This is similar to the dispersal patterns of modern-day hominins which have a multi-male kinship-based society, as opposed to the harem society of gorillas and other primates. However, the small canines of males compared to those of females would seem to suggest a much lower degree of male–male aggression than non-human hominins. Males did not seem to have ventured very far from the valley, which could either indicate small home ranges, or that they preferred dolomitic landscapes due to perhaps cave abundance or factors related to vegetation growth.


Pathology

In a sample of ten ''A. africanus'' specimens, seven exhibited mild to moderate alveolar bone loss resulting from periodontal disease (the wearing away of the bone which supports the teeth due to gum disease). The juvenile specimen STS 24a was diagnosed with an extreme case of periodontal disease on the right side of the mouth, which caused pathological bone growth around the affected site, and movement of the first two right molars during cyclical periods of bacterial infection and resultant inflammation. Similarly, the individual appears to have preferred to chew using the left side of the jaw. The periodontal disease would have severely hindered chewing, particularly in the last year of life, and the individual potentially may have relied on group members to survive for as long as it did. In 1992, anthropologists Geoffrey Raymond Fisk and Gabriele Macho interpreted the left ankle bone Stw 363 as bearing evidence of a healed
calcaneal fracture A calcaneal fracture is a break of the calcaneus (heel bone). Symptoms may include pain, bruising, trouble walking, and deformity of the heel. It may be associated with breaks of the hip or back. It usually occurs when a person lands on their f ...
on the heel bone (which was not preserved), which they believed resulted from a fall from a tree. If correct, then the individual was able to survive for a long time despite losing a great deal of function in the left leg. However, they also noted that similar damage could potentially have also been inflicted by calcite deposition and crystallisation during the fossilisation process. Calcaneal fractures have been recorded in humans, and are present quite often in arboreal primates.


Palaeoecology

South African australopithecines appear to lived in an area with a wide range of habitats. At Sterkfontein, fossil wood belonging to the
liana A liana is a long- stemmed, woody vine that is rooted in the soil at ground level and uses trees, as well as other means of vertical support, to climb up to the canopy in search of direct sunlight. The word ''liana'' does not refer to a t ...
'' Dichapetalum cf. mombuttense'' was recovered. The only living member of this tree genus in South Africa is '' Dichapetalum cymosum'', which grows in dense, humid gallery forests. In modern day, ''D. mombuttense'' only grows in the Congolian rainforests, so its presence could potentially mean the area was an extension of this rainforest. The wildlife assemblages indicate a mix of habitats such as
bush savanna In physical geography, a steppe () is an ecoregion characterized by grassland plains without trees apart from those near rivers and lakes. Steppe biomes may include: * the montane grasslands and shrublands biome * the temperate grasslands, ...
, open
woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see ...
, or grassland. The
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from tree ...
'' Anastrabe integerrima'' was also found, which today only grows on the wetter South African coastline. This could indicate the Cradle of Humankind received more rainfall in the Plio-Pleistocene. In total, the Cradle of Humankind may have featured gallery forests surrounded by grasslands. Taung also appears to have featured a wet, closed environment. Australopithecines and early ''Homo'' likely preferred cooler conditions than later ''Homo'', as there are no australopithecine sites that were below in elevation at the time of deposition. This would mean that, like chimps, they often inhabited areas with an average diurnal temperature of , dropping to at night. In 1983, studying ''P. robustus'' remains, South African palaeontologist Charles Kimberlin Brain hypothesised that australopithecine bones accumulated in caves due to large carnivore activity, dragging in carcasses. He was unsure if these predators actively sought them out and brought them back to the cave den to eat, or inhabited deeper recesses of caves and ambushed them when they entered. Baboons in this region modern day often shelter in
sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
s especially on cold winter nights, though Brain proposed that australopithecines seasonally migrated out of the Highveld and into the warmer
Bushveld The Bushveld (from af, bosveld, af, bos 'bush' and af, veld) is a sub-tropical woodland ecoregion of Southern Africa. It encompasses most of Limpopo Province and a small part of the North West Province of South Africa, the Central and Nort ...
, only taking up cave shelters in spring and autumn. The ''A. africanus'' fossils from Sterkfontein Member 4 were likely accumulated by big cats, though hunting hyenas and jackals may have also played a role. Scratches, gouges, and puncture marks on the Taung child similar to those inflicted by modern crowned eagles indicate this individual was killed by a bird of prey. Around 2.07 million years ago, just before the arrival of ''P. robustus'' and ''H. erectus'', ''A. africanus'' became extinct in the Cradle of Humankind. It is possible that South Africa was a refuge for ''Australopithecus'' until the beginning of major climatic variability and volatility, and, perhaps, competition with ''Homo'' and ''Paranthropus''.


See also


References


Further reading

*


External links


MNSU

''Australopithecus africanus''
- The Smithsonian Institution's Human Origins Program


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

Human Timeline (Interactive)
Smithsonian,
National Museum of Natural History The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. In 2021, with 7. ...
(August 2016). {{DEFAULTSORT:Australopithecus Africanus Australopithecus Pliocene primates Prehistoric South Africa Mammals described in 1925 Fossil taxa described in 1925 Pliocene mammals of Africa Taxa named by Raymond Dart