| Australopithecus garhi Temporal range:Gelasian, 2.6–2.5 Ma | |
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| Reconstruction of the skull at theNational Museum of Ethiopia | |
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. garhi |
| Binomial name | |
| †Australopithecus garhi Asfaw et al., 1997 | |
Australopithecus garhi is a species ofaustralopithecine from theBouri Formation in theAfar Region of Ethiopia 2.6–2.5 million years ago (mya) during theEarly Pleistocene. The first remains were described in 1999 based on several skeletal elements uncovered in the three years preceding.A. garhi was originally considered to have been a direct ancestor toHomo and the human line, but is now thought to have been an offshoot. Like other australopithecines,A. garhi had a brain volume of 450 cc (27 cu in); a jaw which jutted out (prognathism); relatively largemolars andpremolars; adaptations for both walking on two legs (bipedalism) and grasping while climbing (arboreality); and it is possible that, though unclear if, males were larger than females (exhibitedsexual dimorphism). One individual, presumed female based on size, may have been 140 cm (4 ft 7 in) tall.
A. garhi is the first pre-Homo hominin postulated to have manufactured tools—using them in butchering—and may be counted among a growing body of evidence for pre-Homo stone tool industries (the ability to manufacture tools was previously believed to have separatedHomo from predecessors.)A. garhi possibly produced theOldowanindustry which was previously considered to have been invented by the laterH. habilis, though this may have instead been produced by contemporaryHomo.
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Like other australopithecines,A. garhi had a brain volume of about 450 cc (27 cu in), asagittal crest running along the midline of the skull, and aprognathic jaw (the jaw jutted out). Relatively, the postcanine teeth, themolars andpremolars, are massive (post-canine megadontia), similar to or greater than those of other australopithecines and of the large-toothedParanthropus robustus.[1]
Like the earlierA. afarensis from the same region,A. garhi had a humanlike humerus to femur ratio, and an apelike brachial index (lower to upper arm ratio) as well as curvedphalanges of the hand.[1] This is generally interpreted as adaptations for both walking on two legs (habitualbipedalism) as well as for grasping while climbing in trees (arboreality).[2]
The BOU-VP-35/1 humerus specimen is notably larger than the humerus of the BOU-VP-12/1 specimen, which could potentially indicate size-specificsexual dimorphism with males larger than females to a similar degree to what is postulated inA. afarensis, but it is unclear if this does not represent normal size variation of the same sex as this is based on only two specimens. Nonetheless, on the basis of size, BOU-VP-12/130 is considered male and BOU-VP-17/1 female. Contemporary hominins from Kenya are about the same size asA. garhi.[1] BOU-VP-17/1 may have been about 140 cm (4 ft 7 in) tall.[3]
Australopithecus are thought to have had fast, apelike growth rates, lacking an extended childhood typical of modern humans. However, the legs ofA. garhi are elongated, unlike those of otherAustralopithecus, and, in humans, elongated limbs develop during the delayed adolescent growth spurt. This could mean thatA. garhi, compared to otherAustralopithecus, either had a slower overall growth rate, or a more rapid leg growth rate.[2]
The EthiopianAustralopithecus garhi was first described in 1999 by palaeoanthropologistsBerhane Asfaw,Tim D. White,Owen Lovejoy, Bruce Latimer, Scott Simpson, andGen Suwa based on fossils discovered in the Hatayae Beds of theBouri Formation inMiddle Awash,Afar Region, Ethiopia. The first hominin remains were discovered here in 1990—a partialparietal bone (GAM-VP-1/2), left jawbone (GAM-VP-1/1), and lefthumerus (MAT-VP-1/1)—which are unassignable to a specificgenus. The first identifiableAustralopithecus fossils–an adultulna (BOU-VP-11/1)–were found on 17 November 1996 by T. Assebework. A partial skeleton (BOU-VP-12/1) was discovered 13 days later by White, comprising a mostly complete leftfemur, righthumerus,radius, andulna, and a partialfibula, foot, and jawbone. Theholotype specimen, a partial skull (BOU-VP-12/130), was discovered on 20 November 1997 by Ethiopian palaeoanthropologistYohannes Haile-Selassie. More skull fragments (BOU-VP-12/87) were recovered 50 m (160 ft) south of BOU-VP-12/1. On 17 November 1997, French palaeoanthropologist Alban Defleur discovered a complete mandible (BOU-VP-17/1) about 9 km (5.6 mi) north in the Esa Dibolocality of the formation, and American palaeoanthropologist David DeGusta discovered a humerus (BOU-VP-35/1) 1 km (0.62 mi) north of BOU-VP-17/1. However, BOU-VP-11, -12, and -35 cannot conclusively be attributed toA. garhi.[1]
The remains are dated to about 2.5 million years ago (mya) based onargon–argon dating. When they were discovered, human evolution was obscured due to a paucity of remains from 3 to 2 mya, with the onlyhominins from this timespan being identified from South Africa (A. africanus) andLake Turkana, Kenya (Paranthropus aethiopicus). Likewise, the classification ofaustralopithecines and pre-Homo erectus hominins has been the subject of much debate. The original describers consideredA. garhi to be a descendant of the earlierA. afarensis which inhabited the same region, based mainly on dental similarities. Though they assigned the species toAustralopithecus, the original describers believed it could represent an ancestor toHomo, which, if the case, would possibly lead to reclassification asH. garhi. Because the characteristics ofA. garhi are unexpected for a human ancestor at this stage, thespecific name,garhi, means "surprise" in the localAfar language.[1][3] In 1999, American palaeoanthropologists David Strait andFrederick E. Grine concluded thatA. garhi was instead an offshoot of the human line instead of an ancestor becauseA. garhi andHomo share nosynapomorphies (traits unique to only them).[4][5] In 2015,Homo was recorded from 2.8 mya, much earlier thanA. garhi.[6]
The large teeth ofAustralopithecus species have historically been interpreted as having been adaptations for a diet of hard foods, but the durable teeth may instead have only served an important function during leaner times for harder fallback foods. That is, dental anatomy may not accurately portray normalAustralopithecus diet, rather abnormal diet during times of famine.[7]
Though it was not found with any tools, mammalian bones associated with theA. garhi remains exhibit cut and percussion marks made from stone tools: the leftmandible of analcelaphinebovid with three successive, unambiguous cut marks presumably made while removing the tongue; a bovidtibia with cut marks, chop marks, and impact scars from ahammerstone, possibly inflicted to harvest thebone marrow; and aHipparion (a horse) femur with cut marks consistent with dismemberment and filleting. As to why stone tools were not present, because the Hatayae locality was likely a featureless, grassy lake margin with so few raw materials for making stone tools, it is possible these hominins were creating and carrying tools some ways with them to butchering sites, intending to use them many times before discarding. It was previously believed that onlyHomo could manufacture tools;[8][3] but it is also possible that the butcherers were not manufacturing tools and simply used naturally sharp rocks.[9]
At the nearby Gona site, where there is an abundance of raw materials, severalOldowan tools (anindustry previously believed to have been invented byH. habilis) were recovered from 1992 to 1994. The tools date to around 2.6–2.5 mya, the oldest evidence of manufacturing at the time, and sinceA. garhi was the only species identified in the vicinity at the time, this species was the best candidate for authorship.[10][11] However, in 2015, the earliest remains ofHomo,LD 350-1, were discovered inLedi-Geraru, also in the Afar Region, dating to 2.8–2.75 mya.[6] More stone tools were found in 2019 dating to about 2.6 mya in Ledi-Geraru, predating the Gona artifacts, and these may be attributed toHomo; the invention of sharp-edged Oldowan tools could actually be due to specific adaptations characteristic ofHomo.[12] Nonetheless, other australopithecines have been associated with stone tool manufacturing, such as the 2010 discovery of cut marks dating to 3.4 mya attributed toA. afarensis,[9] and the 2015 discovery of theLomekwi culture from Lake Turkana dating to 3.3 mya possibly attributed toKenyanthropus.[13]
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