Australopithecus africanus
Australopithecus africanus Temporal range:
Late Pliocene - Early Pleistocene | |
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Mrs. Ples, at the University of Zurich | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Primates |
Suborder: | Haplorhini |
Infraorder: | Simiiformes |
Family: | Hominidae |
Subfamily: | Homininae |
Tribe: | Hominini |
Genus: | †Australopithecus |
Species: | †A. africanus
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Binomial name | |
†Australopithecus africanus Dart, 1925
| |
Synonyms | |
Australopithecus africanus is an
A. africanus brain volume was about 420–510 cc (26–31 cu in). Like other early hominins, the
A. africanus, unlike most other primates, seems to have exploited
million years ago ) |
Research history
In 1924, Australian anatomist Professor
A. africanus was the first evidence that humans evolved in Africa, as
On this thesis man's predecessors differed from living apes in being confirmed killers: carnivorous creatures, that seized living quarries by violence, battered them to death, tore apart their broken bodies, dismembered them limb from limb, slaking their ravenous thirst with the hot blood of victims and greedily devouring livid writhing flesh.
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",[5][6] and in 1938 moved it into a new genus as "Plesianthropus transvaalensis". He also discovered the robust australopithecine Paranthropus robustus, showing evidence of a wide diversity of Early Pleistocene "man-apes".[7] Before World War II, 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.[2]: 289–290 In 1947, the most complete skull was discovered, STS 5 ("Mrs. Ples").[8] Wider acceptance of A. africanus prompted re-evaluation of Piltdown Man in 1953, revealing its falsehood.[2]: 290
In 1949, Dart recommended splitting a presumed-female facial fragment from
In addition to Taung, Sterkfontein, and Makapansgat, A. africanus was in 1992 discovered in
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.[21] The discovery of Early Pleistocene 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.[22] It is also suggested that A. africanus is closely related to P. robustus but not to the other Paranthropus species in East Africa,[23] or that A. africanus is ancestral to all Paranthropus.[24] 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.[25]
Anatomy
Skull
Based on 4 specimens, the A. africanus brain volume averaged about 420–510 cc (26–31 cu in). Based on this, neonatal brain size was estimated to have been 165.5–190 cc (10.10–11.59 cu in) 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%.
A. africanus had a
Build
In 1992, American anthropologist Henry McHenry estimated an average weight (when assuming humanlike or apelike body proportions, respectively) of 40.8 or 52.8 kg (90 or 116 lb) for males based on five partial leg specimens, and 30.2 or 36.8 kg (67 or 81 lb) for females based on seven specimens.[29] In 2015, American anthropologist William L. Jungers and colleagues similarly reported an average weight (without attempting to distinguish males from females) of 30.7 kg (68 lb) with a range of 22.8–43.3 kg (50–95 lb) for weight based on 19 specimens.[30] Based on seven specimens, McHenry estimated that males, on average, grew to 138 cm (4 ft 6 in) tall and females 125 cm (4 ft 1 in).[31] In 2017, based on 24 specimens, anthropologist Manuel Will and colleagues estimated a height of 124.4 cm (4 ft 1 in) with a range of 110–142 cm (3 ft 7 in – 4 ft 8 in).[32] The elderly, probably female StW 573 was estimated to have stood about 130 cm (4 ft 3 in).[33]: 7
Based on the A. afarensis skeleton
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.
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
The leg bones clearly show that A. africanus habitually engaged in bipedal locomotion, though some aspects of the
The arms of StW 573 were about 53.4 cm (1 ft 9 in), and her legs 61.5 cm (2 ft 0 in). 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 humans at 64.5–78%, chimpanzees about 100%, gorillas 100–125%, and orangutans 135–150.9%.[33]: 17–18
Palaeobiology
Diet
In 1954, Robinson proposed that A. africanus was a generalist omnivore 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 organs, or perhaps grass-eating invertebrates (such as locusts or termites), grazing mammals, or insectivores or carnivores. Most primates do not eat C4 plants.[44][45] 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.[46] Still, A. africanus, like chimps, may have required hammerstones to crack open nuts (such as marula nuts), though A. africanus is not associated with any tools.[44]
A. africanus conspicuously lacks evidence of dental
Barium 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 and strontium 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.[50]
Society
The group dynamics of australopithecines is difficult to predict with any degree of accuracy. A 2011
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).[52] 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.[53]
In 1992, anthropologists Geoffrey Raymond Fisk and Gabriele Macho interpreted the left ankle bone Stw 363 as bearing evidence of a healed calcaneal fracture 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.[54]
Palaeoecology
South African australopithecines appear to lived in an area with a wide range of habitats. At Sterkfontein,
In 1983, studying P. robustus remains, South African palaeontologist
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.[62]
See also
- African archaeology
- Australopithecus afarensis – Extinct hominid from the Pliocene of East Africa
- Australopithecus sediba – Two-million-year-old hominin from the Cradle of Humankind
- Homo ergaster – Extinct species or subspecies of archaic human
- Homo rudolfensis – Extinct hominin from the Early Pleistocene of East Africa
- Homo habilis – Archaic human species from 2.8 to 1.65 mya
- LD 350-1 – Earliest known specimen of the genus Homo
- Makapansgat pebble – pebble found by early humans, resembles a face
- Paranthropus robustus – Extinct species of hominin of South Africa
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Further reading
- ISBN 978-0-404-15910-8.
External links
- MNSU
- Australopithecus africanus - The Smithsonian Institution's Human Origins Program
- Handprint
- 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 (August 2016).