Australopithecus


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Related to Australopithecus: Australopithecus africanus

Australopithecus

(ôstrā'lōpĭth`əkəs, –pəthē`kəs), an extinct hominin genus found in Africa between about 4 and 1 million years ago. At least seven species of australopithecines are now generally recognized, including Australopithecus afarensis, A. africanus, A. bahrelghazali, A. anamensis, A. boisei, A. robustus, and A. aethiopicus. There is considerable disagreement, however, among experts on the number of species that should be included within the genus. Some of the species are considered by some experts to belong to other genera, and some remains classified among the above species by some experts are considered by other experts to belong to additional Australopithecus species. Two of the seven species listed above—A. bahrelghazali and A. anamensis—are based on very fragmentary remains. Among the many anatomical traits shared by these species were a fully erect posture and bipedal gait (though the degree to which all the species could comfortably walk upright on the ground is a matter of dispute). The most "primitive" anatomical feature was a small and apelike braincase, comparable in size to those of gorillas and chimpanzees when measured relative to overall body size. Other species that have been reported found include A. garhi in Ethiopia in 1999, A. prometheus in 1948 and the 1990s in South Africa, and A. sediba in 2008–9 in South Africa.

A. afarensis, dating to at least 3.75 million years ago, may be ancestral to all the other species of this genus, with the exception of A. anamensis, a hominin dating to c.4.1 million years ago, discovered in 1994. A. afarensis is known from fossils found at a number of sites in Ethiopia and at Laetoli, Tanzania. The 3.6-million-year-old footprints, preserved in volcanic ash at Laetoli, are commonly attributed to this species. Postcranial skeletal remains show that A. afarensis was relatively small, standing 3.5 to 5 ft (1 to 1.6 m) tall and weighing 45 to 110 lb (20 to 50 kg).

Remains of an australopithecine of similar size and between 2 to 3 million years old have also been found in S Africa. Known as A. africanus, it had molars slightly larger than A. afarensis, but in other respects it had decidedly more human features than A. afarensis, including a higher forehead, less prominent brow ridges, and a shorter face. Most researchers consider A. africanus to be a distinct species that is descended from A. afarensis.

Two other well-known australopithecines, A. boisei (from E Africa) and A. robustus (from S Africa), featured very large molars and premolars, very thick jaws, and craniums topped by prominent crests. These features probably reflect a relatively specialized diet of rough vegetable matter. In contrast, A. afarensis and A. africanus had cranio-dental features consistent with a more generalized diet. The large-toothed australopithecines also had skeletons indicative of a heavier build than the small-toothed australopithecines; the former are believed to have weighed 25 to 50 lb (10 to 20 kg) more than the latter, even though they were approximately the same height. Based on these pronounced differences, australopithecines are classified into two distinct types: gracile and robust. The robust australopithecines all became extinct between 1.5 and 1 million years ago, while one of the gracile autralophithecines is believed to have given rise to the branch leading to the emergence of the genus Homo c.2.5 million years ago.

The species A. barhelghazali is attributed to a 3.5-million-year-old jaw and tooth remains found in central Chad in 1995. The first remains of an Australopithecus recovered outside of E or S Africa, this find suggests hominin evolution took place over a much larger portion of Africa than many experts had originally believed. A cranium specimen recovered from W Turkana, Kenya, is attributed to the robust species A. aethiopicus. This fossil is 2.5 million year old and shares certain primitive features with A. afarensis, providing strong evidence that the robust A. aethiopicus descended from the gracile A. afarensis. Many experts believe A. aethiopicus subsequently gave rise to the two major robust species, A. boisei and A. robustus. Tibia and mandible fragments from Allia Bay, Lake Turkana, are attributed to yet another species, A. amarensis, providing evidence for bipedalism c.4.1 million years ago.

There is no consensus among the experts concerning the evolutionary relationship among the various australopithecines, or between the australopithecines and Homo habilis, which is considered by many to be the earliest species of the genus Homo. One proposal is that A. afarensis gave rise to two distinct lineages c.3 million years ago: One branch became the robust australopithecines (doomed to extinction), while the other branch became the gracile species (one species of which eventually evolved into H. habilis). Many researchers believe that the species that evolved into H. habilis was A. africanus. Other experts reject this model, as well as the claim that A. africanus played any such key role. Increasingly, specialists favor assigning the robust australopithecines to a completely seperate genus, Paranthropus, because of the very significant physical differences between the robust and gracile species. According to this view, A. afarensis was the last common ancestor of these two distinct types of hominins.

See also human evolutionhuman evolution,
theory of the origins of the human species, Homo sapiens. Modern understanding of human origins is derived largely from the findings of paleontology, anthropology, and genetics, and involves the process of natural selection (see Darwinism).
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Bibliography

See D. C. Johanson and M. A. Edey, Lucy: The Beginnings of Humankind (1981); E. Delson, ed., Ancestors: The Hard Evidence (1985); R. Leakey and R. Lewin, Origins Reconsidered (1992).

Australopithecus

[ȯ‚strā·lō′pith·ə·kəs]
(paleontology)
A genus of near-men in the subfamily Australopithecinae representing a side branch of human evolution.
References in periodicals archive ?
Other lesser-known Australopithecus fossils date back at least 3.9 million years, but they featured only jaws and teeth.
Australopithecus africanus lived from about two to three million years ago during a period of major climatic and ecological change in South Africa, and the species was characterised by a combination of human-like and retained ape-like traits.
How astonishing would it be that something resembling Australopithecus would have survived a long, long, way from the African Rift Valley as recently as 50,000 years ago?
She knelt down and pressed her forehead against the Plexiglas case that contained the Australopithecus skull.
Shape of the teeth and flatness of the cheek bones are the prominent features Australopithecus Africanus.
naledi's collarbone and upper arm bone resemble corresponding Australopithecus bones, she reported.
While I was an undergraduate anthropology student as at Miami University, exciting word came out of discoveries of Australopithecus fossils in East Africa.
Asimismo, otro estudio publicado en abril de este ano por la revista Nature, informa que la especie Australopithecus prometheus, representada por el esqueleto de Little Foot (pies pequenos, en ingles) vivio hace unos 3.6 millones de anos; es decir pudo ser coetanea de la de Lucy, pero era mas grande y alta (mas de metro y medio de estatura), con hombros muy fuertes, brazos largos y tambien con una marcha bipeda.
The most famous of these is Australopithecus afarensis known as Lucy who lived between 2.9-3.8m years ago, and was initially thought to be our direct ancestor.
This fossil represents a species, Australopithecus afarensis, that at one 'dine was thought to be the closest relative of humans.
The specimens, dubbed Australopithecus sediba, have an unusual mix of features.
Anthropologists think that Australopithecus sediba, as he's known scientifically, may be the immediate ancestor of humans.