Australopithecus anamensis

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Australopithecus anamensis
Temporal range: Pliocene
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Subfamily: Homininae
Genus: Australopithecus
Species: A. anamensis
Binomial name
Australopithecus anamensis
M.G. Leakey et al., 1995

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 [1][2] and Ethiopia,[3] representing over 20 individuals.

Discovery[edit]

A. anamensis bone at the University of Zurich

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.[citation needed]

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.[citation needed]

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.[citation needed]

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".[1] 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,[4] with recent findings from stratigraphic sequences dating to about 4.1–4.2 million years ago.[3] 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.[citation needed]

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. These new fossils, sampled from a woodland context, include the largest hominid canine tooth yet recovered and the earliest Australopithecus femur.[3] 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.[5]

See also[edit]

References[edit]

  1. ^ a b M. G. Leakey, C. S. Feibel, I. MacDougall & A. Walker (1995-08-17). "New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya". Nature 376 (6541): 565–571. Bibcode:1995Natur.376..565L. doi:10.1038/376565a0. PMID 7637803. 
  2. ^ M. G. Leakey, C. S. Feibel, I. McDougall, C. Ward & A. Walker (1998-05-07). "New specimens and confirmation of an early age for Australopithecus anamensis". Nature 393 (6680): 62–66. Bibcode:1998Natur.393...62L. doi:10.1038/29972. PMID 9590689. 
  3. ^ a b c T. D. White, G. WoldeGabriel, B. Asfaw, S. Ambrose, Y. Beyene, R. L. Bernor, J.-R. Boisserie, B. Currie, H. Gilbert, Y. Haile-Selassie, W. K. Hart, L. J. Hlusko, F. C. Howell, R. T. Kono, T. Lehmann, A. Louchart, C. O. Lovejoy, P. R. Renne, H. Saegusa, E. S. Vrba, H. Wesselman & G. Suwa (2006-04-13). "Asa Issie, Aramis and the origin of Australopithecus". Nature 440 (7086): 883–889. Bibcode:2006Natur.440..883W. doi:10.1038/nature04629. PMID 16612373. 
  4. ^ McHenry, Henry M (2009). "Human Evolution". In Michael Ruse & Joseph Travis (eds). Evolution: The First Four Billion Years. pp. 256–280. ISBN 978-0-674-03175-3.  (see pp.263-265)
  5. ^ Borenstein, Seth. "New Fossil Links Up Human Evolution". The Associated Press. Retrieved 2006-04-13. [dead link]

External links[edit]