Furthermore, because e.g.A. africanus is more closely related to humans, or their ancestors at the time, than e.g.A. anamensis and many moreAustralopithecus branches,Australopithecus cannot be consolidated into a coherent grouping without also including theHomo 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 ChadianA. bahrelghazali indicates that the genus was much more widespread than the fossil record suggests), before eventually becoming extinct 1.9 million years ago (or 1.2 to 0.6 million years ago ifParanthropus is included). While none of the groups normally directly assigned to this group survived,Australopithecus gave rise to living descendants, as the genusHomo emerged from anAustralopithecus species[7][9][10][11][12][excessive citations] at some time between 3 and 2 million years ago.[13]
Australopithecus possessed two of the three duplicated genes derived fromSRGAP2 roughly 3.4 and 2.4 million years ago (SRGAP2B andSRGAP2C), the second of which contributed to the increase in number and migration ofneurons in the human brain.[14][15] Significant changes to the hand first appear in the fossil record of laterA. afarensis about 3 million years ago (fingers shortened relative to thumb and changes to the joints between theindex finger and thetrapezium andcapitate).[16]
The firstAustralopithecus specimen, thetype specimen, was discovered in 1924 in a lime quarry by workers atTaung, South Africa. The specimen was studied by the Australian anatomistRaymond Dart, who was then working at theUniversity of the Witwatersrand inJohannesburg. The fossil skull was from a three-year-oldbipedal primate (nicknamedTaung Child) that he namedAustralopithecus africanus. The first report was published inNature 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.[17] Later, Scottish paleontologistRobert Broom and Dart set out to search for more early hominin specimens, and several moreA. 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.[17]
In 1950, evolutionary biologistErnst Walter Mayr said that all bipedal apes should be classified into the genusHomo, and considered renamingAustralopithecus toHomo transvaalensis.[18] However, the contrary view taken by J.T. Robinson in 1954, excluding australopiths fromHomo, became the prevalent view.[18] The first australopithecine fossil discovered in eastern Africa was anA. boisei skull excavated byMary Leakey in 1959 inOlduvai Gorge,Tanzania. Since then, the Leakey family has continued to excavate the gorge, uncovering further evidence for australopithecines, as well as forHomo habilis andHomo erectus.[17] The scientific community took 20 more years to widely acceptAustralopithecus as a member of the human family tree.
In 1997, an almost completeAustralopithecus skeleton with skull was found in theSterkfontein caves ofGauteng, South Africa. It is now called "Little Foot" and it is around 3.7 million years old. It was namedAustralopithecus prometheus[19][20] which has since been placed withinA. africanus. Other fossil remains found in the same cave in 2008 were namedAustralopithecus sediba, which lived 1.9 million years ago.A. africanus probably evolved intoA. sediba, which some scientists think may have evolved intoH. erectus,[21] though this is heavily disputed.
In 2003, Spanish writerCamilo José Cela Conde and evolutionary biologistFrancisco J. Ayala proposed resurrecting the genusPraeanthropus to houseOrrorin,A. afarensis,A. anamensis,A. bahrelghazali, andA. garhi,[22] but this genus has been largely dismissed.[23]
With the apparent emergence of the generaHomo,Kenyanthropus, andParanthropus in the genusAustralopithecus,taxonomy runs into some difficulty, as the name of species incorporates their genus. According tocladistics, groups should not be leftparaphyletic, where it is kept not consisting of a common ancestor and all of its descendants.[24][25][26][27][28][29] Resolving this problem would cause major ramifications in the nomenclature of all descendent species. Possibilities suggested have been to renameHomo sapiens toAustralopithecus sapiens[30] (or evenPan sapiens[31][32]), or to move someAustralopithecus species into new genera.[8] A study reported in 2025 reported preliminary success in extracting ancient proteins from an Australopithic tooth, suggesting thatpaleoproteomics has the potential to provide information about the genetic affinities of the species.[33]
In 2002 and again in 2007, Camilo José Cela Condeet al. suggested thatA. africanus be moved toParanthropus.[7] On the basis of craniodental evidence, Strait and Grine (2004) suggest thatA. anamensis andA. garhi should be assigned to new genera.[34] It is debated whether or notA. bahrelghazali should be considered simply a western variant ofA. afarensis instead of a separate species.[35][36]
Australopiths shared several traits with modern apes and humans, and were widespread throughoutEastern andNorthern Africa by 3.5 million years ago (mya). The earliest evidence of fundamentally bipedal hominins is a (3.6 mya)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.[38]
According to theChimpanzee Genome Project, thehuman–chimpanzee last common ancestor existed about five to six million years ago, assuming a constant rate of mutation. However, hominin species dated to earlier than the date could call this into question.[39]Sahelanthropus tchadensis, commonly called "Toumai", is about seven million years old andOrrorin 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.[39]
The brains of most species ofAustralopithecus were roughly 35% of the size of a modern human brain[40] with anendocranial volume average of 466 cc (28.4 cu in).[13] Although this is more than the average endocranial volume ofchimpanzee brains at 360 cc (22 cu in)[13] the earliest australopiths (A. anamensis) appear to have been within the chimpanzee range,[37] whereas some later australopith specimens have a larger endocranial volume than that of some early Homo fossils.[13]
Most species ofAustralopithecus 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 ofsexual dimorphism, males being larger than females.[41] In modern populations, males are on average a mere 15% larger than females, while inAustralopithecus, 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.[41] One paper finds thatA. afarensis had a level of dimorphism close to modern humans.[42]
According to A. Zihlman,Australopithecus body proportions closely resemble those ofbonobos (Pan paniscus),[43] leading evolutionary biologistJeremy Griffith to suggest that bonobos may be phenotypically similar toAustralopithecus.[44] Furthermore, thermoregulatory models suggest that australopiths were fully hair covered, more like chimpanzees and bonobos, and unlike humans.[45]
Reconstruction of a largely hairless maleA. sediba by Adrie and Alfons Kennis at theNeanderthal Museum, Germany
The fossil record seems to indicate thatAustralopithecus is ancestral toHomo and modern humans. It was once assumed that large brain size had been a precursor to bipedalism, but the discovery ofAustralopithecus 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.[citation needed] Earlier fossils, such asOrrorin 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.[46] Major changes to the pelvis and feet had already taken place beforeAustralopithecus.[47] It was once thought that humans descended from aknuckle-walking ancestor,[48] but this is not well-supported.[49]
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.[50] The molars ofAustralopithecus 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.[50] However, australopiths generally evolved a larger postcanine dentition with thicker enamel.[51] Australopiths in general had thickenamel, likeHomo, while other great apes have markedly thinner enamel.[50] Robust australopiths wore their molar surfaces down flat, unlike the more gracile species, who kept their crests.[50]
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 speciesA. africanus andParanthropus robustus. Early analyses ofdental microwear in these two species showed, compared toP. robustus,A. africanus had fewer microwear features and more scratches as opposed to pits on its molar wear facets.[52] Microwear patterns on the cheek teeth ofA. afarensis andA. anamensis indicate thatA. afarensis predominantly ate fruits and leaves, whereasA. anamensis included grasses and seeds (in addition to fruits and leaves).[53] 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.[50]
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.[54] In 2005, fossil animal bones with butchery marks dating to 2.6 million years old were found at the site ofGona, Ethiopia. This implies meat consumption by at least one of three species of hominins occurring around that time:A. africanus,A. garhi, and/orP. aethiopicus.[55] 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.[56] However, a 2025 study measuring nitrogen isotope ratios in fossilized teeth determined thatAustralopithecus was almost entirely vegetarian.[57][58]
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.[50] However, such divergence in chewing adaptations may instead have been a response to fallback food availability. In leaner times, robust and gracile australopithecines may have turned to different low-quality foods (fibrous plants for the former, and hard food for the latter), but in more bountiful times, they had more variable and overlapping diets.[59][60] In a 1979 preliminary microwear study ofAustralopithecus fossil teeth, anthropologist Alan Walker theorized that robust australopiths ate predominantly fruit (frugivory).[61]
It is debated if theAustralopithecus hand was anatomically capable of producing stone tools.[63]A. garhi was associated with large mammal bones bearing evidence of processing by stone tools, which may indicate australopithecine tool production.[64][65][66][67] Stone tools dating to roughly the same time asA. garhi (about 2.6 mya) were later discovered at the nearbyGona andLedi-Geraru sites, but the appearance ofHomo at Ledi-Geraru (LD 350-1) casts doubt on australopithecine authorship.[68]
In 2010, cut marks dating to 3.4 mya on abovid leg were found at theDikaka site, which were at first attributed to butchery byA. afarensis,[69] but because the fossil came from asandstone unit (and were modified by abrasive sand and gravel particles during the fossilisation process), the attribution to butchery is dubious.[70]
In 2015, theLomekwi culture was discovered at Lake Turkana dating to 3.3 mya, possibly attributable toKenyanthropus[71] orA. deyiremeda.[72]
^Toth, Nicholas and Schick, Kathy (2005). "African Origins" inThe Human Past: World Prehistory and the Development of Human Societies (Editor: Chris Scarre). London: Thames and Hudson. Page 60.ISBN0-500-28531-4
^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,
^Tattersall, I. (2017). "Species, genera, and phylogenetic structure in the human fossil record: a modest proposal".Evolutionary Anthropology: Issues, News, and Reviews.26 (3):116–118.doi:10.1002/evan.21523.PMID28627785.S2CID43487900.Forms such asArdipithecus,Sahelanthropus, andOrrorin 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...
^Kimbel, William H. (2015), "The Species and Diversity of Australopiths", in Henke, Winfried; Tattersall, Ian (eds.),Handbook of Paleoanthropology, Springer Berlin Heidelberg, pp. 2071–2105,doi:10.1007/978-3-642-39979-4_50,ISBN9783642399787
^Schwarz, J.H. (2004). "Barking up the wrong ape--australopiths and the quest for chimpanzee characters in hominid fossils".Collegium Antropologicum.28 (Suppl 2):87–101.PMID15571084.S2CID12944654.
^Ward, Carol V.; Hammind, Ashley S. (2016)."Australopithecus and Kin".Nature Education Knowledge.7 (3): 1. Retrieved2019-11-13.
^White, Tim D. (2002). "Chapter 24 Earliest Hominids". In Hartwig, Walter Carl (ed.).The Primate Fossil Record (Cambridge Studies in Biological and Evolutionary Anthropology).Cambridge University Press.ISBN0-521-66315-6.
^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.
^McHenry, H. M. (2009)."Human Evolution". In Michael Ruse; Joseph Travis (eds.).Evolution: The First Four Billion Years. Cambridge, Massachusetts: The Belknap Press of Harvard University Press. pp. 261–265.ISBN978-0-674-03175-3.
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