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Australopithecus

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Australopithecus
Temporal range: Pliocene
Australopithecus afarensis
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Primates
Family:
Hominidae
Genus:
Australopithecus

R.A. Dart, 1925
Species
Map of the fossil sites of the early Australopithecines in Africa

Australopithecus (Latin for "southern ape"[1]) is a genus of extinct hominids closely related to humans.

There were many different species of Australopithecus. They all lived in the Late Miocene sub-epoch.[2] The earliest Australopithecus fossils are from around 4.4 million years ago; the most recent are from around 1.4 million years ago.[3] All were found in East Africa.

The genus Homo, and hence human beings, probably developed from a group of hominids that included Australopithecus.[4]

Famous australopithecine fossils include the Taung Child (which is around 2.8 million years old) and Lucy (around 3.2 million years old[3]).

Discovery

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Raymond Dart was the first to describe Australopithecus. In 1925 he discovered and wrote about the Taung Child, an Australopithecus fossil skull. It was the first fossil ever to show evidence that human ancestors walked on two feet.[5]

The genus Australopithecus originally included two rather different forms. Scientists originally called them the gracile australopithecines and the robust australopithecines.[2]

The "gracile" australopithecines were lightweight. This article describes this type of australopithecine. Gracile australopithecines shared several traits with modern apes and humans.[6]

See the main article: Paranthropus

Originally, scientists identified another group called the robust australopithecines. Scientists now call these Paranthropus.[7]

Scholars do not agree on whether Australopithecus and Paranthropus should be put in separate genera. Some say Paranthropus is just another species of Australopithecus, not its own genus.[7]

Morphology

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Original skull of a male Australopithecus africanus

Brain size

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All australopithecines had smaller brains than modern humans do. For example, Australopithecus africanus had an average brain volume of 450 cc, about the same size as a modern chimpanzee's brain.[8]

Brain size in hominins did not increase significantly until the genus Homo appeared.[8]

Other features

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The Taung specimen had short canine teeth, and the position of the foramen magnum was evidence that the Taung Child walked on two feet.[9] Fossil footprints[10] found in Laetoli, Tanzania also show that these apes had achieved bipedalism.

Skeleton

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Most species of Australopithecus were small and gracile, usually standing between 1.2 and 1.4 m tall (approx. 4 to 4.5 feet). Australopithecines showed more sexual dimorphism than modern hominids do.

Modern humans display a low degree of sexual dimorphism, with males being only 15% larger (taller, heavier) than females, on average.[11] In Australopithecus, however, the largest males could be up to to 50% larger than females.[12]

Evolution

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A reconstruction of Australopithecus sediba

Ancestors of Homo?

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Scholars used to think that Australopithecus africanus was the ancestor of the genus Homo (in particular Homo erectus). However, scientists have now found fossils from the genus Homo that are older than A. africanus.[13] This leaves two possibilities. The genus Homo may have split off from the genus Australopithecus at an earlier date. Their latest common ancestor might have been A. afarensis[14][15] or an even earlier form, possibly Kenyanthropus platyops[16]. Another possibility is that both Homo and Australopithecus developed independently from the same common ancestor.

When did human and chimps split?

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According to the Chimpanzee Genome Project, both human (Ardipithecus, Australopithecus and Homo) and chimpanzee (Pan troglodytes and Pan paniscus) lineages diverged from a common ancestor about 5 to 6 million years ago, if we assume a constant rate of evolution.[source?]

Toumai and Orrorin

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However, hominins discovered more recently are somewhat older than the molecular clock would suggest. Sahelanthropus tchadensis, commonly called "Toumai", is about 7 million years old[17], and Orrorin tugenensis lived at least 6 million years ago.[18] Since little is known of them, they remain controversial because the molecular clock in humans has determined that humans and chimpanzees had an evolutionary split at least a million years later.[source?]

Theories

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One theory suggests that the human and chimpanzee lineages diverged somewhat at first, then some populations interbred around one million years after diverging.[19] More likely, the assumptions behind molecular clocks do not hold exactly. The key assumption behind the technique is that, in the long run, changes in molecular structure happen at a steady rate.[further explanation needed] Researchers such as Ayala have challenged this assumption.[20][21][22]

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References

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  1. ↑ Latin australis = 'of the south', Greek pithekos = 'ape'
  2. 1 2 Mai, L. L.; Owl, M. Y.; Kersting, M. P. (2005). The Cambridge Dictionary of Human Biology and Evolution. Cambridge & New York: Cambridge University Press. p. 45. ISBN 978-0-521-66486-8.
  3. 1 2 "Australopithecus | Characteristics & Facts | Britannica". Encyclopedia Britannica. Retrieved 2025-12-14.
  4. ↑ Leakey, Richard 1994. The origin of humankind. New York: BasicBooks. ISBN 0465031358
  5. ↑ "Taung Child". The Smithsonian Institution's Human Origins Program. Retrieved 2025-12-14.
  6. ↑ Welker, Barbara Helm (2017-06-13). "9. Gracile Australopiths". The History of Our Tribe: Hominini. Open SUNY Textbooks. ISBN 978-1-942341-40-6.
  7. 1 2 "The "Robust" Australopiths | Learn Science at Scitable". www.nature.com. Retrieved 2025-12-15.
  8. 1 2 "Larger brains". The Australian Museum. Retrieved 2025-12-14.
  9. ↑ The foramen is a hole in the bottom of the skull, through which the spinal cord joins the brain. In apes it is positioned at the rear of the skull, in humans near the middle. The foramen of a bipedal ape would be expected to be more like humans.
  10. ↑ These footprints have been dated to 3.7 million years ago.
  11. ↑ "Sexual Body Size Dimorphism | Center for Academic Research and Training in Anthropogeny (CARTA)". carta.anthropogeny.org. Retrieved 2025-12-15.
  12. ↑ Beck, Roger B. (1999). World history: patterns of interaction. Linda Black, Larry S. Krieger, Phillip C. Naylor, Dahia Ibo Shabaka. Evans ton, IL: McDougal Littell. ISBN 0-395-87274-X.
  13. ↑ "Science: Oldest Fossil of Homo Genus Found in Ethiopia | American Association for the Advancement of Science (AAAS)". www.aaas.org. Retrieved 2025-12-15.
  14. ↑ "Australopithecus afarensis". The Smithsonian Institution's Human Origins Program. Retrieved 2025-12-15.
  15. ↑ "Study challenges claim that 2-million-year-old fossil is human ancestor". www.uchicagomedicine.org. Retrieved 2025-12-15.
  16. ↑ "Kenyanthropus platyops". The Smithsonian Institution's Human Origins Program. Retrieved 2025-12-15.
  17. ↑ "Sahelanthropus tchadensis". The Smithsonian Institution's Human Origins Program. Retrieved 2025-12-15.
  18. ↑ "Orrorin tugenensis". The Smithsonian Institution's Human Origins Program. Retrieved 2025-12-15.
  19. ↑ Bower, Bruce (May 20, 2006). "Hybrid-driven evolution: genomes show complexity of human-chimp split". Science News. 169 (20): 308. doi:10.2307/4019102. JSTOR 4019102.
  20. ↑ Ayala F.J. (1999). "Molecular clock mirages". BioEssays. 21 (1): 71–75. doi:10.1002/(SICI)1521-1878(199901)21:1<71::AID-BIES9>3.0.CO;2-B. PMID 10070256. Archived from the original on 2012-12-16. Retrieved 2011-02-28.
  21. ↑ Schwartz, Jeffrey H.; Maresca, Bruno (December 2006). "Do Molecular Clocks Run at All? A Critique of Molecular Systematics". Biological Theory. 1 (4): 357–371. doi:10.1162/biot.2006.1.4.357. ISSN 1555-5542. S2CID 28166727.
  22. ↑ Jarmila Kukalová-Peck. 2008. Phylogeny of higher taxa in insecta: finding synapomorphies in the extant fauna and separating them from homoplasies. Evolutionary Biology 35, 4-51
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