Australopithecus

Source: Wikipedia, the free encyclopedia.
For the collective tribe, see Australopithecine.

Australopithecus
Temporal range: Zanclean – Gelasian, 4.5–1.9/1.2 mya
↓
Mrs. Ples, an Australopithecus africanus specimen
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Subtribe: Australopithecina
Genus: †Australopithecus
R.A. Dart, 1925
Type species
†Australopithecus africanus
Dart, 1925
Species

Classically excluded but cladistically included:

Australopithecus (

Australopithecina,[3][4] which sometimes also includes Ardipithecus,[5] though the term "australopithecine" is sometimes used to refer only to members of Australopithecus. Species include A. garhi, A. africanus, A. sediba, A. afarensis, A. anamensis, A. bahrelghazali and A. deyiremeda. Debate exists as to whether some Australopithecus species should be reclassified into new genera, or if Paranthropus and Kenyanthropus are synonymous with Australopithecus, in part because of the taxonomic inconsistency.[6][7]

Furthermore, because e.g. A. africanus is more closely related to for instance humans, or their ancestors at the time, than e.g. A. anamensis and many more Australopithecus branches, Australopithecus cannot be consolidated into a coherent grouping without also including the Homo genus and other genera.

The earliest known member of the genus, A. anamensis, existed in eastern Africa around 4.2 million years ago. Australopithecus fossils become more widely dispersed throughout eastern and southern Africa (the Chadian A. bahrelghazali indicates the genus was much more widespread than the fossil record suggests), before eventually becoming pseudo-extinct 1.9 million years ago (or 1.2 to 0.6 million years ago if Paranthropus is included). While none of the groups normally directly assigned to this group survived, Australopithecus gave rise to living descendants, as the genus Homo emerged from an Australopithecus species[6][8][9][10][11][excessive citations] at some time between 3 and 2 million years ago.[12]

Australopithecus possessed two of three duplicated genes derived from

capitate).[15]

Taxonomy

Research history

Taung Child's skull

The first Australopithecus specimen, the

bipedal primate (nicknamed Taung Child) that he named Australopithecus africanus. The first report was published in Nature in February 1925. Dart realised that the fossil contained a number of humanoid features, and so he came to the conclusion that this was an early human ancestor.[16] Later, Scottish paleontologist Robert Broom and Dart set out to search for more early hominin specimens, and several more A. africanus remains from various sites. Initially, anthropologists were largely hostile to the idea that these discoveries were anything but apes, though this changed during the late 1940s.[16]

In 1950, evolutionary biologist

Ernst Walter Mayr said that all bipedal apes should be classified into the genus Homo, and considered renaming Australopithecus to Homo transvaalensis.[17] However, the contrary view taken by Robinson in 1954, excluding australopiths from Homo, became the prevalent view.[17] The first australopithecine fossil discovered in eastern Africa was an A. boisei skull excavated by Mary Leakey in 1959 in Olduvai Gorge, Tanzania. Since then, the Leakey family has continued to excavate the gorge, uncovering further evidence for australopithecines, as well as for Homo habilis and Homo erectus.[16]
The scientific community took 20 more years to widely accept Australopithecus as a member of the human family tree.

In 1997, an almost complete Australopithecus skeleton with skull was found in the

Australopithecus prometheus[18][19] which has since been placed within A. africanus. Other fossil remains found in the same cave in 2008 were named Australopithecus sediba, which lived 1.9 million years ago. A. africanus probably evolved into A. sediba, which some scientists think may have evolved into H. erectus,[20]
though this is heavily disputed.

In 2003, Spanish writer Camilo José Cela Conde and evolutionary biologist Francisco J. Ayala proposed resurrecting the genus Praeanthropus to house Orrorin, A. afarensis, A. anamensis, A. bahrelghazali, and A. garhi,[21] but this genus has been largely dismissed.[22]

Classification

With the apparent emergence of the genera

paraphyletic, where it is kept not consisting of a common ancestor and all of its descendants.[23][24][25][26][27][28] Resolving this problem would cause major ramifications in the nomenclature of all descendent species. Possibilities suggested have been to rename Homo sapiens to Australopithecus sapiens[29] (or even Pan sapiens[30][31]), or to move some Australopithecus species into new genera.[7]

In 2002 and again in 2007, Cele-Conde et al. suggested that A. africanus be moved to Paranthropus.[6] On the basis of craniodental evidence, Strait and Grine (2004) suggest that A. anamensis and A. garhi should be assigned to new genera.[32] It is debated whether or not A. bahrelghazali should be considered simply a western variant of A. afarensis instead of a separate species.[33][34]

African
hominin timeline (in mya)
View references
H. sapiensH. nalediH. rhodesiensisH. ergasterAu. sedibaP. robustusP. boiseiH. rudolfensisH. habilisAu. garhiP. aethiopicusLD 350-1K. platyopsAu. bahrelghazaliAu. deyiremedaAu. africanusAu. afarensisAu. anamensisAr. ramidusAr. kadabba


Evolution

Map of the fossil sites of the early australopithecines in Africa

A. anamensis may have descended from or was closely related to Ardipithecus ramidus.[35] A. anamensis shows some similarities to both Ar. ramidus and Sahelanthropus.[35]

Australopiths shared several traits with modern apes and humans, and were widespread throughout

fossil trackway in Laetoli, Tanzania, which bears a remarkable similarity to those of modern humans. The footprints have generally been classified as australopith, as they are the only form of prehuman hominins known to have existed in that region at that time.[36]

According to the

Orrorin tugenensis lived at least six million years ago. Since little is known of them, they remain controversial among scientists since the molecular clock in humans has determined that humans and chimpanzees had a genetic split at least a million years later.[citation needed] One theory suggests that the human and chimpanzee lineages diverged somewhat at first, then some populations interbred around one million years after diverging.[37]

Anatomy

Reconstruction of a largely hairless male A. sediba by Adrie and Alfons Kennis at the Neanderthal Museum, Germany

The brains of most species of Australopithecus were roughly 35% of the size of a modern human brain[38] with an endocranial volume average of 466 cc (28.4 cu in).[12] Although this is more than the average endocranial volume of chimpanzee brains at 360 cc (22 cu in)[12] the earliest australopiths (A. anamensis) appear to have been within the chimpanzee range,[35] whereas some later australopith specimens have a larger endocranial volume than that of some early Homo fossils.[12]

Most species of Australopithecus were diminutive and gracile, usually standing 1.2 to 1.4 m (3 ft 11 in to 4 ft 7 in) tall. It is possible that they exhibited a considerable degree of sexual dimorphism, males being larger than females.[39] In modern populations, males are on average a mere 15% larger than females, while in Australopithecus, males could be up to 50% larger than females by some estimates. However, the degree of sexual dimorphism is debated due to the fragmentary nature of australopith remains.[39] One paper finds that A. afarensis had a level of dimorphism close to modern humans.[40]

According to A. Zihlman, Australopithecus body proportions closely resemble those of bonobos (Pan paniscus),[41] leading evolutionary biologist Jeremy Griffith to suggest that bonobos may be phenotypically similar to Australopithecus.[42] Furthermore, thermoregulatory models suggest that australopiths were fully hair covered, more like chimpanzees and bonobos, and unlike humans.[43]

Smithsonian National Museum of Natural History
. This reconstruction depicts the facultative bipedalism hypothesis, indicated by the use of the tree for stabilization.

The fossil record seems to indicate that Australopithecus is ancestral to Homo and modern humans. It was once assumed that large brain size had been a precursor to bipedalism, but the discovery of Australopithecus with a small brain but developed bipedality upset this theory. Nonetheless, it remains a matter of controversy as to how bipedalism first emerged. The advantages of bipedalism were that it left the hands free to grasp objects (e.g., carry food and young), and allowed the eyes to look over tall grasses for possible food sources or predators, but it is also argued that these advantages were not significant enough to cause the emergence of bipedalism.[

Orrorin tugenensis, indicate bipedalism around six million years ago, around the time of the split between humans and chimpanzees indicated by genetic studies. This suggests that erect, straight-legged walking originated as an adaptation to tree-dwelling.[44] Major changes to the pelvis and feet had already taken place before Australopithecus.[45] It was once thought that humans descended from a knuckle-walking ancestor,[46] but this is not well-supported.[47]

Australopithecines have thirty-two teeth, like modern humans. Their molars were parallel, like those of great apes, and they had a slight pre-canine gap (diastema). Their canines were smaller, like modern humans, and with the teeth less interlocked than in previous hominins. In fact, in some australopithecines, the canines are shaped more like incisors.[48] The molars of Australopithecus fit together in much the same way those of humans do, with low crowns and four low, rounded cusps used for crushing. They have cutting edges on the crests.[48] However, australopiths generally evolved a larger postcanine dentition with thicker enamel.[49] Australopiths in general had thick enamel, like Homo, while other great apes have markedly thinner enamel.[48] Robust australopiths wore their molar surfaces down flat, unlike the more gracile species, who kept their crests.[48]

Diet

The robust Paranthropus boisei (left) vs the gracile A. anamensis (right)

Australopithecus species are thought to have eaten mainly fruit, vegetables, and tubers, and perhaps easy-to-catch animals such as small lizards. Much research has focused on a comparison between the South African species A. africanus and Paranthropus robustus. Early analyses of dental microwear in these two species showed, compared to P. robustus, A. africanus had fewer microwear features and more scratches as opposed to pits on its molar wear facets.[50] Microwear patterns on the cheek teeth of A. afarensis and A. anamensis indicate that A. afarensis predominantly ate fruits and leaves, whereas A. anamensis included grasses and seeds (in addition to fruits and leaves).[51] The thickening of enamel in australopiths may have been a response to eating more ground-bound foods such as tubers, nuts, and cereal grains with gritty dirt and other small particulates which would wear away enamel. Gracile australopiths had larger incisors, which indicates tearing food was important, perhaps eating scavenged meat. Nonetheless, the wearing patterns on the teeth support a largely herbivorous diet.[48]

In 1992, trace-element studies of the strontium/calcium ratios in robust australopith fossils suggested the possibility of animal consumption, as they did in 1994 using stable carbon isotopic analysis.[52] In 2005, fossil animal bones with butchery marks dating to 2.6 million years old were found at the site of Gona, Ethiopia. This implies meat consumption by at least one of three species of hominins occurring around that time: A. africanus, A. garhi, and/or P. aethiopicus.[53] In 2010, fossils of butchered animal bones dated 3.4 million years old were found in Ethiopia, close to regions where australopith fossils were found.[54]

Robust australopithecines (Paranthropus) had larger cheek teeth than gracile australopiths, possibly because robust australopithecines had more tough, fibrous plant material in their diets, whereas gracile australopiths ate more hard and brittle foods.

frugivory).[57]

A study in 2018 found

acid erosion, on the teeth of A. africanus, probably caused by consumption of acidic fruit.[58]

Technology

It is debated if the Australopithecus hand was anatomically capable of producing stone tools.[59] A. garhi was associated with large mammal bones bearing evidence of processing by stone tools may indicate australopithecine tool production.[60][61][62][63] Stone tools dating to roughly the same time as A. garhi (about 2.6 mya) were later discovered at the nearby Gona and Ledi-Geraru sites, but the appearance of Homo at Ledi-Geraru (LD 350-1) casts doubt on australopithecine authorship.[64]

In 2010, cut marks dating to 3.4 mya on a

bovid leg were found at the Dikaka site, which were at first attributed to butchery by A. afarensis,[65] but because the fossil came from a sandstone unit (and were modified by abrasive sand and gravel particles during the fossilisation process), the attribution to butchery is dubious.[66]

In 2015, the Lomekwi culture was discovered at Lake Turkana dating to 3.3 mya, possibly attributable to Kenyanthropus[67] or A. deyiremeda.[68]

Notable specimens

  • KT-12/H1
    , an A. bahrelghazali mandibular fragment, discovered 1995 in Sahara, Chad
  • AL 129-1, an A. afarensis knee joint, discovered 1973 in Hadar, Ethiopia
  • Karabo, a juvenile male A. sediba, discovered in South Africa
  • Laetoli footprints, preserved hominin footprints in Tanzania
  • Lucy, a 40%-complete skeleton of a female A. afarensis, discovered 1974 in Hadar, Ethiopia
  • Selam, remains of a three-year-old A. afarensis female, discovered in Dikika, Ethiopia
  • MRD-VP-1/1, first skull of A. anamensis discovered in 2016 in Afar, Ethiopia.
  • STS 5 (Mrs. Ples), the most complete skull of an A. africanus ever found in South Africa
  • STS 14, remains of an A. africanus, discovered 1947 in Sterkfontein, South Africa
  • STS 71, skull of an A. africanus, discovered 1947 in Sterkfontein, South Africa
  • Taung Child, skull of a young A. africanus, discovered 1924 in Taung, South Africa

Gallery

  • The spot where the first Australopithecus boisei was discovered in Tanzania.
    The spot where the first Australopithecus boisei was discovered in Tanzania.
  • Original skull of Mrs. Ples, a female A. africanus
    Original skull of Mrs. Ples, a female A. africanus
  • Taung Child by Cicero Moraes, Arc-Team, Antrocom NPO, Museum of the University of Padua.
    Taung Child by Cicero Moraes, Arc-Team, Antrocom NPO, Museum of the University of Padua.
  • Cast of the skeleton of Lucy, an A. afarensis
    Cast of the skeleton of Lucy, an A. afarensis
  • Skull of the Taung child
    Skull of the Taung child

See also

References

  1. ISBN 978-3-12-539683-8
  2. ^ "Glossary. American Museum of Natural History". Archived from the original on 20 November 2021.
  3. ^ Wood & Richmond 2000.
  4. ^ Briggs & Crowther 2008, p. 124.
  5. ^ Wood 2010.
  6. ^
    PMID 20855306
    .
  7. ^ a b Hawks, John (2017-03-20). "The plot to kill Homo habilis". Medium. Retrieved 2019-03-24.
  8. PMID 10213683
    .
  9. Bradshaw Foundation
    . Retrieved 2019-11-11.
  10. S2CID 14209370
    .
  11. ISBN 0-500-28531-4
  12. ^
    PMID 27298460
    .
  13. ^ Reardon, Sara (2012-05-03). "The humanity switch: How one gene made us brainier". New Scientist. Retrieved 2020-03-06.
  14. PMID 28333212
    .
  15. PMID 18380869
    .
  16. ^
    ISBN 0632043091
    .
  17. ^
    S2CID 206639783
    .
  18. ^ 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,
  19. ^ "New stratigraphic research makes Little Foot the oldest complete Australopithecus".
  20. ^ Celia W. Dugger; John Noble Wilford (April 8, 2010). "New Hominid Species Discovered in South Africa". The New York Times.
  21. PMID 12794185
    .
  22. S2CID 43487900
    . Forms such as Ardipithecus, Sahelanthropus, and Orrorin have also been admitted to the pantheon, though this has clearly been facilitated by their great age. And in a nod to history, the venerable genus Paranthropus has been grandfathered in for use by those who think it useful. But except for the widely dismissed revival of Praeanthropus, there has been little real rethinking of the hugely minimalist hominid taxonomy, generic as well as specific, that Mayr foisted on us all those years ago...
  23. ISBN 9783642399787
  24. ISBN 9780123786333
    .
  25. S2CID 12944654
    .
  26. PMID 29574829
    .
  27. PMID 29380889
    .
  28. ^ "2 @BULLET Enhanced cognitive capacity as a contingent fact of hominid phylogeny". ResearchGate. Retrieved 2019-01-12.
  29. PMID 25112991
    .
  30. ISBN 9781472414090
    .
  31. ISBN 9780141042220
    .
  32. PMID 15566946
    .
  33. ^ Ward, Carol V.; Hammind, Ashley S. (2016). "Australopithecus and Kin". Nature Education Knowledge. 7 (3): 1. Retrieved 2019-11-13.
  34. ISBN 0-521-66315-6
    .
  35. ^
    S2CID 201656331
    .
  36. PMID 20339543
    .
  37. ^
    JSTOR 4019102
    .
  38. ^ "Australopithecus afarensis". The Smithsonian Institution's Human Origins Program. 2010-01-25. Retrieved 2020-01-09.
  39. ^
    ISBN 978-0-395-87274-1
    .
  40. ^ Reno, Philip L., Richard S. Meindl, Melanie A. McCollum, and C. Owen Lovejoy. 2003."Sexual Dimorphism in Australopithecus Afarensis Was Similar to That of Modern Humans." Proceedings of the National Academy of Sciences 100 (16): 9404–9. https://doi.org/10.1073/pnas.1133180100.
  41. S2CID 4252525
    .
  42. ISBN 978-1-74129-011-0
    . Retrieved 28 March 2013.
  43. PMID 27178459
    .
  44. S2CID 85992565
    .
  45. PMID 3212438
    .
  46. PMID 11786992
    .
  47. PMID 19667206
    .
  48. ^ a b c d e f Kay, R.F., 1985, 'DENTAL EVIDENCE FOR THE DIET OF AUSTRALOPITHECUS', Annual Review of Anthropology, 14, pp. 315-341.
  49. ISBN 978-0-674-03175-3
    .
  50. doi:10.1016/S0047-2484(86)80010-0
    .
  51. PMID 27851745
    .
  52. ^ Billings, Tom. "Comparative Anatomy and Physiology Brought Up to Date--continued, Part 3B)". Archived from the original on 15 December 2006. Retrieved 2007-01-06.
  53. ^ Nature. "Evidence for Meat-Eating by Early Humans".
  54. doi:10.1038/news.2010.399
    .
  55. PMID 18446200
    .
  56. S2CID 4431062
    .
  57. ^ Rensberger, Boyce (1979-05-15). "Teeth Show Fruit Was The Staple". The New York Times. Retrieved 11 August 2021.
  58. S2CID 52056962
    .
  59. ISSN 1631-0683
    .
  60. S2CID 4331652
    .
  61. PMID 14529651
    .
  62. PMID 10213683
    .
  63. PMID 10213682
    .
  64. PMID 31160451
    .
  65. S2CID 4356816
    .
  66. PMID 21078985
    .
  67. S2CID 1207285
    .
  68. S2CID 4472489
    .

Sources

Further reading

External links

Wikibooks has a book on the topic of: Introduction to Paleoanthropology
Wikimedia Commons has media related to Australopithecus.
Wikispecies has information related to Australopithecus.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Australopithecus&oldid=1218958297"