Australopithecus africanus

Australopithecus africanus
Temporal range: Pliocene
Natural endocranial cast (485 cm3) (Sts 60), articulated with a fragmentary skull still embedded in breccia (TM 1511)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Family: Hominidae
Tribe: Hominini
Genus: †Australopithecus
Species: † A. africanus
Binomial name
Australopithecus africanus
Dart, 1925 [1]

Australopithecus africanus was an early hominid, an australopithecine, who lived between ~3.03 and 2.04 million years ago in the later Pliocene and early Pleistocene.[2] In common with the older Australopithecus afarensis, Au. africanus was of slender build, or gracile, and was thought to have been a direct ancestor of modern humans. Fossil remains indicate that Au. africanus was significantly more like modern humans than Au. afarensis, with a more human-like cranium permitting a larger brain and more humanoid facial features. Au. africanus has been found at only four sites in southern Africa — Taung (1924), Sterkfontein (1935), Makapansgat (1948) and Gladysvale (1992).[1]

Famous fossils

Taung Child

Main article: Taung Child
Cast of the Taung Child.

Raymond Dart became interested in fossils found at the lime mine at Taung near Kimberley, South Africa in 1924.[3][4] The most promising of these was a skull of an odd ape-creature sharing human traits such as eye orbits, teeth, and, most importantly, the hole at the base of the skull over the spinal column (the foramen magnum) indicating a human-like posture. Dart assigned the specimen the name Australopithecus africanus ("southern ape of Africa").[1]

This was the first time the word Australopithecus was assigned to any hominid. Dart claimed that the skull must have been an intermediate species between ape and humans, but his claim about the Taung Child was rejected by the scientific community at the time due to the belief that a large cranial capacity must precede bipedal locomotion.[1] This was exacerbated by the widespread acceptance of the Piltdown Man. Sir Arthur Keith, a fellow anatomist and anthropologist, suggested that the skull belonged to a young ape, most likely from an infant gorilla. It was not until 20 years later that the public accepted the new genus and that australopithecines were a true member of Homininae.

Mrs. Ples

Main article: Mrs. Ples
Skull of "Mrs. Ples", Transvaal Museum Pretoria.

Dart's theory was supported by Robert Broom.[5] In 1938 Broom classified an adult endocranial cast having a brain capacity of 485 cc, which had been found by G. W. Barlow, as Plesianthropus transvaalensis. On April 18, 1947, Broom and John T. Robinson discovered a skull belonging to a middle-aged female,[6] (catalogue number STS 5), while blasting at Sterkfontein. Broom classified it also as Plesianthropus transvaalensis, and it was dubbed Mrs. Ples by Broom's young coworkers (though the skull is now thought to have belonged to a young male). The lack of facial projection in comparison to apes was noted by Raymond Dart (including from Taung Child), a trait in common with more advanced hominines. Both fossils were later classified as Australopithecus africanus.

Morphology and interpretations

Like Au. afarensis, Au. africanus the South African counterpart was generally similar in many traits, a bipedal hominid with arms slightly larger than the legs (a physical trait also found in chimpanzees). Despite its slightly more human-like cranial features, seen for example in the crania Mrs. Ples and STS 71, other more primitive features including ape-like curved fingers for tree climbing are also present.

Due to other more primitive features visible on Au. africanus, some researchers believe the hominin, instead of being a direct ancestor of more modern hominins, evolved into Paranthropus. One robust australopithecine seen as a descendent of Au. africanus is Paranthropus robustus. Both P. robustus and Au. africanus crania seem very alike despite the more heavily built features of P. robustus that are adaptations for heavy chewing like a gorilla. Au. africanus, on the other hand, had a cranium which quite closely resembled that of a chimp, yet both their brains measure about 400 cc to 500 cc and probably had an ape-like intelligence.[5] Au. africanus had a pelvis that was built for slightly better bipedalism than that of Au. afarensis. A 2015 study of hand bones in Au. africanus indicated that the species had "human-like trabecular bone pattern in the metacarpals consistent with forceful opposition of the thumb and fingers typically adopted during tool use," a pattern that would be consistent with an earlier adoption of tool manufacture and use than had been thought likely.[7]

Sexual dimorphism

Recent evidence regarding modern human sexual dimorphism (physical differences between men and women) in the lumbar spine has been seen in pre-modern primates such as Au. africanus. This dimorphism has been seen as an evolutionary adaptation of females to better bear lumbar load during pregnancy, an adaptation that non-bipedal primates would not need to make.[8][9]

A 2011 study using ratios of strontium isotopes in teeth suggested that Au. africanus and Paranthropus robustus groups in southern Africa were patrilocal: women tended to settle farther from their region of birth than men did.[10][11]

Geochronology

The Little Foot specimen most recent dating estimates it to 3.67 million years old[12] which gives some support to a claim by its discoverer, Ronald J. Clarke, that it may a previously unknown species, named Australopithecus prometheus by Raymond Dart, with similaritites to Paranthropus robustus. However, the specimen has usually been lumped into A. africanus by most workers.[13][14] Earlier attempts dates it between 3.03 and 2.04 million years [15] based on a combination of palaeomagnetism, electron spin resonance and faunal dating.[16] The Makapansgat fossils date to between 3.03 and 2.58 million years with fossils MLD37/38 likely dating close to 2.58 million years; Sterkfontein dates to between 2.58 and 2.04 million years with the Sts 5 Mrs Ples fossil dating to around 2.04 million years; and Gladysvale dates to between 2.4 and 2.0 million years. The age of the Taung child remains more difficult to determine and is the focus of a current project by Brian Kuhn, Phil Hopley, Colin Menter and Andy Herries.

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 Australopithecus africanus
  2. ↑ Human Ancestors Hall: Tree
  3. ↑ Raymond Dart and our African origins
  4. ↑ TalkOrigins Archive — Biographies: Raymond Dart
  5. ↑ 5.0 5.1 Primate Origins
  6. ↑ John T. Robinson
  7. ↑ Skinner MM; Stephens, NB; Tsegai, ZJ; Foote, AC; Nguyen, NH; Gross, T; Pahr, DH; Hublin, JJ; Kivell, TL et al. (2015). "Human-like hand use in Australopithecus africanus". Science 347 (6220): 395–399. doi:10.1126/science.1261735.
  8. ↑ The Independent's article A pregnant woman's spine is her flexible friend, by Steve Connor from The Independent (Published: 13 December 2007) quoting Shapiro, Liza, University of Texas at Austin Dept. of Anthropology about her article, Whitcome, et al., Nature advance online publication, (2007) doi:10.1038/nature06342 .
  9. ↑ Why Pregnant Women Don't Tip Over. Amitabh Avasthi for National Geographic News, December 12, 2007. This article has good pictures explaining the differences between bipedal and non-bipedal pregnancy loads.
  10. ↑ Bowdler, Neil (2 June 2011). "Ancient cave women 'left childhood homes'". BBC News. Retrieved 2011-06-02.
  11. ↑ Copeland SR; Sponheimer, Matt; De Ruiter, Darryl J.; Lee-Thorp, Julia A.; Codron, Daryl; Le Roux, Petrus J.; Grimes, Vaughan; Richards, Michael P. et al. (2011). "Strontium isotope evidence for landscape use by early hominins". Nature 474 (7349): 76–78. doi:10.1038/nature10149. PMID 21637256.
  12. ↑ Gardner., Elizabeth K.; Purdue University (April 1, 2015). "New instrument dates old skeleton before 'Lucy'; 'Little Foot' 3.67 million years old". Science Daily. Retrieved April 3, 2015.
  13. ↑ BRUXELLES L., CLARKE R. J., MAIRE R., ORTEGA R., et STRATFORD D. – 2014. - Stratigraphic analysis of the Sterkfontein StW 573 Australopithecus skeleton and implications for its age. Journal of Human Evolution.
  14. ↑ http://phys.org/news/2014-03-stratigraphic-foot-oldest-australopithecus.html
  15. ↑ =Herries, A.I.R., Shaw, J. 2011. Palaeomagnetic analysis of the Sterkfontein palaeocave deposits; age implications for the hominin fossils and stone tool industries. J. Human Evolution. 60, 523-539.
  16. ↑ =Herries, A.I.R.., Hopley, P., Adams, J., Curnoe, D., Maslin, M. 2010. Geochronology and palaeoenvironments of the South African early hominin bearing sites: a reply to ‘Wrangham et al., 2009: Shallow-Water Habitats as Sources of Fallback Foods for Hominins’ Am. J. Phys. Anthro. 143, 640–646.

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