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''Australopithecus anamensis'' (or ''Praeanthropus anamensis'') is a stem-human species that lived approximately four million years ago. Nearly one hundred fossil specimens are known from Kenya and Ethiopia, representing over 20 individuals. It is accepted that ''A. anamensis'' is ancestral to ''A. afarensis'' and continued an evolving lineage. Fossil evidence determines that the ''Australopithecus anamensis'' is the earliest hominin species in the Turkana Basin. Due to an inability to retrieve a massive collection of fossils researchers are not able to make enough observations to differentiate a lot of the early hominids. == Discovery == The first fossilized specimen of the species, though not recognized as such at the time, was a single fragment of humerus (arm bone) found in Pliocene strata in the Kanapoi region of East Lake Turkana by a Harvard University research team in 1965.〔 The specimen was tentatively assigned at the time to ''Australopithecus'' and dated about four million years old. One method used to determine the age of the Kanapoi fossils was based on faunal correlation data, which, established a range between 4.0 and 4.5 mya. Little additional information was uncovered until 1987, when Canadian archaeologist Allan Morton (with Harvard University's Koobi Fora Field School) discovered fragments of a specimen protruding from a partially eroded hillside east of Allia Bay, near Lake Turkana, Kenya. In 1994, the London-born Kenyan paleoanthropologist Meave Leakey and archaeologist Alan Walker excavated the Allia Bay site and uncovered several additional fragments of the hominid, including one complete lower jaw bone which closely resembles that of a common chimpanzee ''(Pan troglodytes)'' but whose teeth bear a greater resemblance to those of a human. Based on the limited postcranial evidence available, ''A. anamensis'' appears to have been habitually bipedal, although it retained some primitive features of its upper limbs. In 1995, Meave Leakey and her associates, taking note of differences between ''Australopithecus afarensis'' and the new finds, assigned them to a new species, ''A. anamensis'', deriving its name from the Turkana word ''anam'', meaning "lake".〔 Leakey determined that this species was independent of many others. It does not represent an intermediate species of any type. Although the excavation team did not find hips, feet or legs, Meave Leakey believes that ''Australopithecus anamensis'' often climbed trees. Tree climbing was one behavior retained by early hominins until the appearance of the first ''Homo'' species about 2.5 million years ago. ''A. anamensis'' shares many traits with ''Australopithecus afarensis'' and may well be its direct predecessor. Fossil records for ''A. anamensis'' have been dated to between 4.2 and 3.9 million years ago,〔 (see pp.263-265)〕 with recent findings from stratigraphic sequences dating to about 4.1–4.2 million years ago.〔 Specimens have been found between two layers of volcanic ash, dated to 4.17 and 4.12 million years, coincidentally when ''A. afarensis'' appears in the fossil record. The fossils (twenty one in total) include upper and lower jaws, cranial fragments, and the upper and lower parts of a leg bone (tibia). In addition to this, the aforementioned fragment of humerus found thirty years ago at the same site at Kanapoi has now been assigned to this species. In 2006, a new ''A. anamensis'' find was officially announced, extending the range of ''A. anamensis'' into north east Ethiopia. Specifically, one site known as Asa Issie provided 30 ''A. anamensis'' fossils. These new fossils, sampled from a woodland context, include the largest hominid canine tooth yet recovered and the earliest ''Australopithecus'' femur.〔 The find was in an area known as Middle Awash, home to several other more modern ''Australopithecus'' finds and only six miles (9.7 kilometers) away from the discovery site of ''Ardipithecus ramidus'', the most modern species of ''Ardipithecus'' yet discovered. ''Ardipithecus'' was a more primitive hominid, considered the next known step below ''Australopithecus'' on the evolutionary tree. The ''A. anamensis'' find is dated to about 4.2 million years ago, the ''Ar. ramidus'' find to 4.4 million years ago, placing only 200,000 years between the two species and filling in yet another blank in the pre-''Australopithecus'' hominid evolutionary timeline. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Australopithecus anamensis」の詳細全文を読む スポンサード リンク
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