Temporal range: Pliocene
M.G. Leakey et al., 1995
Australopithecus anamensis is a hominin species that lived approximately between 4.2 and 3.8 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 Australopithecus anamensis is the earliest hominin species in the Turkana Basin, but likely co-existed with afarensis towards the end of its existence.
The first fossilized specimen of the species, although not recognized as such at the time, was a single fragment of humerus (arm bone) found in Pliocene strata in the Kanapoi region of West Lake Turkana by a Harvard University research team in 1965. Bryan Patterson and William W. Howells's initial paper on the bone was published in Science in 1967; their initial analysis suggested an Australopithecus specimen and an age of 2.5 million years. Patterson and colleagues subsequently revised their estimation of the specimen's age to 4.0–4.5 mya based on faunal correlation data.
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.
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, with findings in the 2000s 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.
In August 2019, scientists announced the discovery of a nearly intact skull, for the first time, and dated to 3.8 million years ago, of A. anamensis in Ethiopia. The skull itself was found by Afar herder Ali Bereino in 2016.
Australopithecus anamensis was found in Kenya, specifically at Allia Bay, East Turkana. Through analysis of stable isotope data, it is believed that their environment had more closed woodland canopies surrounding Lake Turkana than are present today. The greatest density of woodlands at Allia Bay was along the ancestral Omo River. There was believed to be more open savanna in the basin margins or uplands. Similarly at Allia Bay, it is suggested that the environment was much wetter. While it is not definitive, it also could have been possible that nut or seed-bearing trees could have been present at Allia Bay, however more research is needed.
Studies of the microwear on Australopithecus anamensis molar fossils show a pattern of long striations. This pattern is similar to the microwear on the molars of gorillas; suggesting that Australopithecus anamensis had a similar diet to that of the modern gorilla. The microwear patterns are consistent on all Australopithecus anamensis molar fossils regardless of location or time. This shows that their diet largely remained the same no matter what their environment.
The earliest dietary isotope evidence in Turkana Basin hominin species comes from the Australopithecus anamensis. This evidence suggests that their diet consisted primarily of C3 resources, possibly however with a small amount of C4 derived resources. Within the next 1.99- to 1.67-Ma time period, at least two distinctive hominin taxa shifted to a higher level of C4 resource consumption. At this point, there is no known cause for this shift in diet.
- RFI Afrique par Simon Rozé Publié le 28-08-2019 Modifié le 29-08-2019 à 11:00, http://www.rfi.fr/afrique/20190828-ethiopie-decouverte-plus-vieux-fossile-australopitheque
- Leakey, Meave G.; Feibel, Craig S.; MacDougall, Ian; Walker, Alan (17 August 1995). "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.
- Leakey, Meave G.; Feibel, Craig S.; MacDougall, Ian; Ward, Carol; Walker, Alan (7 May 1998). "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.
- White, Tim D.; WoldeGabriel, Giday; Asfaw, Berhane; Ambrose, Stan; Beyene, Yonas; Bernor, Raymond L.; Boisserie, Jean-Renaud; Currie, Brian; Gilbert, Henry; Haile-Selassie, Yohannes; Hart, William K.; Hlusko, Leslea J.; Howell, F. Clark; Kono, Reiko T.; Lehmann, Thomas; Louchart, Antoine; Lovejoy, C. Owen; Renne, Paul R.; Saegusa, Hauro; Vrba, Elisabeth S.; Wesselman, Hank; Suwa, Gen (13 April 2006). "Asa Issie, Aramis and the origin of Australopithecus". Nature. 440 (7086): 883–9. Bibcode:2006Natur.440..883W. doi:10.1038/nature04629. PMID 16612373.
- Kimbel, William H.; Lockwood, Charles A.; Ward, Carol V.; Leakey, Meave G.; Rake, Yoel; Johanson, Donald C. (2006). "Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record". Journal of Human Evolution. 51 (2): 134–152. doi:10.1016/j.jhevol.2006.02.003. PMID 16630646.
- Cerling, Thure E.; Manthi, Fredrick Kyalo; Mbua, Emma N.; Leakey, Louise N.; Leakey, Meave G.; Leakey, Richard E.; Brown, Francis H.; Grine, Frederick E.; Hart, John A.; Kalemeg, Prince; Roche, Hélène; Uno, Kevin T.; Wood, Bernard A. (June 25, 2013). "Stable isotope-based diet reconstructions of Turkana Basin hominins". Proceedings of the National Academy of Sciences of the United States of America. 110 (26): 10501–10506. Bibcode:2013PNAS..11010501C. doi:10.1073/pnas.1222568110. PMC 3696807. PMID 23733966.
- Hanegraef, Hester (4 September 2019). "How the skull of humanity's oldest known ancestor is changing our understanding of evolution". The Conversation. Retrieved 8 September 2019.
- Ward, C; Leaky, M; Walker, A (1999). "The new hominid species Australopithecus anamensis". Evolutionary Anthropology. 7 (6): 197–205. doi:10.1002/(sici)1520-6505(1999)7:6<197::aid-evan4>3.0.co;2-t.
- Patterson, B.; Howells, W. W. (1967). "Hominid Humeral Fragment from Early Pleistocene of Northwestern Kenya". Science. 156 (3771): 64–66. Bibcode:1967Sci...156...64P. doi:10.1126/science.156.3771.64. PMID 6020039.
- Patterson, B; Behrensmeyer, AK; Sill, WD (1970). "Geology and Fauna of a New Pliocene Locality in North-western Kenya". Nature. 226 (5249): 918–921. Bibcode:1970Natur.226..918P. doi:10.1038/226918a0. PMID 16057594.
- C.V., Warda (2001). "Morphology of Australopithecus anamensis from Kanapoi and Allia Bay, Kenya". Journal of Human Evolution. 41 (4): 255–368. doi:10.1006/jhev.2001.0507. PMID 11599925.
- 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)
- Ward, Carol; Manthi, Frederick (September 2008). "New Fossils of Australopithecus Anamensis from Kanapoi, Kenya and Evolution Within the A. Anamensis-Afarensis Lineage". Journal of Vertebrate Paleontology. 28 (Sup 003): 157A. doi:10.1080/02724634.2008.10010459.
- Haile-Selassie, Yohannes; M. Melillo, Stephanie; Vazzana, Antonino; Benazzi, Stefano; Timothy, M. Ryan (2019). "A 3.8-million-year-old hominin cranium from Woranso-Mille, Ethiopia". Nature. doi:10.1038/s41586-019-1513-8. Cite journal requires
- Dvorsky, George (28 August 2019). "Incredible Fossil Discovery Finally Puts a Face on an Elusive Early Hominin". Gizmodo. Retrieved 28 August 2019.
- Greshko, Michael, 'Unprecedented' skull reveals face of human ancestor, National Geographic, August 28, 2019
- Schoeninger, Margaret; Reeser, Holly; Hallin, Kris (September 2003). "Paleoenvironment of Australopithecus anamensis at Allia Bay, East Turkana, Kenya: evidence from mammalian herbivore enamel stable isotopes". Journal of Anthropological Archaeology. 22 (3): 200–207. doi:10.1016/s0278-4165(03)00034-5.
- Ungar, Peter S.; Scott, Robert S.; Grine, Frederick E.; Teaford, Mark F. (20 September 2010). "Molar microwear textures and the diets of Australopithecus anamensis and Australopithecus afarensis". Philosophical Transactions of the Royal Society B: Biological Sciences. 365 (1556): 3345–3354. doi:10.1098/rstb.2010.0033. PMC 2981952. PMID 20855308.