Australopithecus anamensis

One small step for Hominidae, one large step for Homo

By Josie Cowles

Overview

Discovery

Paleoenvironment and Diet

Fossils

Evolutionary Tree

References:

Overview

Australopithecus anamensis was the first hominin species to make the shift from a primarily arboreal setting to the ground. Au. anamensis is the oldest in the genus Australopithecus, living from around 4.2-3.8 mya. To date, Au. anamensis is believed to be the first hominin species to have bipedal adaptations, as well as larger teeth that could process food resources available in more open habitats. What made Au. anamensis stand out from other early hominins was a unique amalgamation of primitive traits, such as a U-shaped dental arcade, and prognathism, and derived traits, such as thick enamel, a thicker ankle, and projecting zygomatics.

From left to right; Chimpanzee dental arcade featuring large pointed canines, a diastema, and a very U-shaped dental arcade; An older hominin with a U-shaped dental arcade and slight diastema; An anatomically modern human with a parabolic dental arcade.

Above image from: https://australian.museum/learn/science/human-evolution/shorter-jaws-with-smaller-teeth/

Overview of cranial morphological changes from early hominins to modern day Homo sapiens

Above image from: https://www.sci.news/othersciences/anthropology/science-hominin-face-evolution-01976.html

Above image: MRD-VP-1/1 and a reconstruction of what Au. anamensis may have looked like, from https://www.science.org/content/article/stunning-ancient-skull-shakes-human-family-tree

Discovery

The first Australopithecus anamensis fossil was discovered in 1965 by paleoanthropologist Bryan Patterson at Kanapoi in West Lake Turkana, Kenya, however the species was not classified until the 1990s. Paleoanthropologist Meave Leakey returned to the Kanapoi site and discovered numerous bone and tooth fragments, leading to the announcement of a new species of Australopithecus called anamensis (Leakey et el. 1995).

Paleoenvironment and Diet

Above image: an artistic recreation of a paleoenvironment in Africa, from: https://novataxa.blogspot.com/2023/09/plesiaceratherium.html

Above image: Modern day Lake Turkana, Kenya. From: https://whc.unesco.org/en/list/801/

Australopithecus anamensis lived in the area that is now known as West Lake Turkana, Kenya. Today it is a very hot and arid area, with little rainfall only between March and May. The vegetation around the lake is mainly shrubs and deserts, with some grasslands appearing in the wet season (African Great Lakes Information Platform, n.d.).

West Lake Turkana between 4.2-3.8 mya had a slightly different climate than at present, but it was still dry and highly seasonal. There was a gallery forest, expansive floodplain grasslands, and dry thorn bushlands (Coffing et al. 1994, Ward et al. 2001). Due to the overwhelming presence of the fish Gymnarchus, as well as Proropterus, scientists believe that there were swamps with muddy water (Coffing et al. 1994). As far as mammals go, some fossils that have been found include the acacia rat Thallomys, and the gerbil Tatera (Coffing et al. 1994 )

Au. anamensis posseses thicker post-canine tooth enamel and larger "cheek teeth" than it's predesessor, Ardipithicus. This suggests a shift in diet from soft, sugary foods to more brittle ones that may have been more readily available in a savanna type environment (Teaford & Ungar 2000, Ungar et al. 2010, Walker 2002).

Above image from: https://www.discovermagazine.com/the-sciences/wooded-grasslands-flourished-in-africa-21-million-years-ago-new-research

Fossils

Numerous fossils have been found to date of Australopithecus anamensis, below four are highlighted.

KNM-KP 29281

This is the type specimen discovered by Peter Nzube at Kanapoi in West Lake Turkana, Kenya in 1994.

Ancestral traits include a U-shaped dental arcade, large front teeth compared to molars, and no chin.

The teeth on this fossil have thick enamel, a trait that is considered derived as previous species had much thinner enamel (Ward et al. 1999, Ward et al. 1999b. Leakey et al. 1995).

Above image: KNM_KP 29281, from: Leakey, M. G., Feibel, C. S., McDougall, I., & Walker, A. (1995). New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya. Nature, 376, 565–571. https://doi.org/10.1038/376565a0. Isaac, C. (2025). Australopithecus anamensis [PowerPoint slides]. Unpublished lecture notes, ANP 440, Michigan State University.

Above image: KNM_KP 271, from: https://x.com/Qafzeh/status/640496520593190912

KNM-KP 271

This is the first Au. anamensis fossil ever found. Bryan Patterson found it in 1965 at Kanapoi, West Lake Turkana, Kenya. It was not initially classified as Au. anamensis, instead it was just considered another find from about 2.5 mya and not mentioned much in further research (Ward et al. 1999, Ward et al. 1999b, Leakey et al. 1995). After Leakey returned to the site and later distinguished Au. anamensis from other hominins, KNM-KP 271 was reclassified due to it being in the same geographic and stratigraphic layer as the other Au. anamensis fossils (Bobe et al. 2020).

KNM-KP 29285

In addition to KNM-KP 29281, Meave Leakey also found the fossilized fragments of the distal and proximal ends of a right tibia at Kanapoi, West Lake Turkana, Kenya, in 1994. This find highlighted that Au. anamensis was bipedal through concave tibial condyles, thicker ankles, and an ankle joint that was perpendicular to the shaft. It also allowed researchers to estimate body mass with regression equations, yielding an estimate of 47-55 kg, or 103-121 lbs (MacLatchy et al. 2010. Leakey et al. 1995)

Above image: KNM_KP 29285 from: MacLatchy, L. M., DeSilva, J., Sanders, W. J., & Wood, B. (2010). Hominini. In L. Werdelin & W. J. Sanders (Eds.), Cenozoic mammals of Africa (pp. 471–540). University of California Press.

MRD-VP-1/1

Above image: MRD-VP-1/1, from: Haile-Selassie, Y. (2021). From trees to the ground: The significance of Australopithecus anamensis in human evolution. L.J.A.R. Distinguished Lecture, Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University

This more recent find by Yohannes Haile-Selassie in 2019 in Woranso-Mille, Ethiopia, is an almost complete Au. anamensis adult male cranium, the first and so far only one discovered. It is believed to be around 3.8 million years old. The cranium exhibits a blend of primitive features, such as a protruding face and small braincase, alongside derived traits like forward-projecting zygomatics. Notably, the age of MRD-VP-1/1 overlaps with that of A. afarensis, suggesting these species coexisted for at least 100,000 years. This challenges the previously held belief of a linear evolutionary transition from A. anamensis to A. afarensis, indicating a more complex evolutionary scenario (Haile-Selassie 2021).

Evolutionary Tree

Prior to the discovery of MRD-VP-1/1, Au. anamensis was thought to be ancestral to Au. afarensis, however with this new discovery it is thought that the two lived around the same time. While the exact relationship of Au. anamensis to our other hominid ancestors is unsure, we do know that it played an important role in our evolution one way or another (Haile-Selassie 2021, Leakey et al 1995, Ward et al 1999, Ward et al 1999b).

Above image: Phylogenetic relationship tree from: Herrera, R. J., & Garcia-Bertrand, R. (2018). Figure 2.4. In R. J. Herrera & R. Garcia-Bertrand (Eds.), Ancestral DNA, human origins, and migrations (pp. 33–60). Academic Press. https://doi.org/10.1016/B978-0-12-804124-6.00002-1

References:

African Great Lakes Information Platform. (n.d.). Lake Turkana. Retrieved April 16, 2025, from https://www.africangreatlakesinform.org/page/lake-turkana
Coffing, K., Feibel, C., Leakey, M. and Walker, A. (1994), Four-million-year-Old hominids from East Lake Turkana, Kenya. Am. J. Phys. Anthropol., 93: 55-65. https://doi.org/10.1002/ajpa.1330930104
René Bobe, Fredrick Kyalo Manthi, Carol V. Ward, J. Michael Plavcan, Susana Carvalho, The ecology of Australopithecus anamensis in the early Pliocene of Kanapoi, Kenya, Journal of Human Evolution, Volume 140, 2020, 102717, ISSN 0047-2484, https://doi.org/10.1016/j.jhevol.2019.102717.
Haile-Selassie, Y. (2021). From trees to the ground: The significance of Australopithecus anamensis in human evolution. L.J.A.R. Distinguished Lecture, Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University.
Leakey, M., Feibel, C., McDougall, I. et al. New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya. Nature 376, 565–571 (1995). https://doi.org/10.1038/376565a0

MacLatchy, L. M., DeSilva, J., Sanders, W. J., & Wood, B. (2010). Hominini. In L. Werdelin & W. J. Sanders (Eds.), Cenozoic mammals of Africa (pp. 471–540). University of California Press

Teaford M. F.& Ungar P. S. (2000) Diet and the evolution of the earliest human ancestors. Proc. Natl. Acad. Sci. USA 97, 13 506–13 511. (doi:10.1073/pnas.260368897).

Ungar Peter S., Scott Robert S., Grine Frederick E. and Teaford Mark F. (2010). Molar microwear textures and the diets of Australopithecus anamensis and Australopithecus afarensisPhil. Trans. R. Soc. B3653345–3354
Walker A. (2002). New perspectives on the hominids of the Turkana Basin, Kenya. Evol. Anthropol. 11((Suppl. 1)), 38–41.
Ward, C. V., Leakey, M. G., & Walker, A. (1999). The new hominid species Australopithecus anamensis. American Journal of Physical Anthropology, 110(1), 1–14. https://doi.org/10.1002/(SICI)1096-8644(199909)110:1<1::AID-AJPA1>3.0.CO;2-I

Ward, C. V., Leakey, M. G., & Walker, A. (1999b). The new hominid species Australopithecus anamensis. Evolutionary Anthropology: Issues, News, and Reviews, 7(6), 197–205. https://doi.org/10.1002/(SICI)1520-6505(1999)7:6<197::AID-EVAN4>3.0.CO;2-T

Ward, C. V., Leakey, M. G., & Walker, A. (2001). Morphology of Australopithecus anamensis from Kanapoi and Allia bay, Kenya. Journal of human evolution, 41(4), 255-368.

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