This species was initially discovered (but not identified) in 1965, by a Harvard expedition led by B. Patterson. A distal end of a humerus (KNM-KP 271) was recovered from a site on the west side of Lake Turkana in Kenya, a site called Kanapoi. For years the specimen's species was debated by those who saw it as Australopithecus, due to its age of approximately 4 myr, and those who saw it as Homo. Fieldwork was not conducted at the site for nearly 30 years, until work began by Meave Leakey et al. The renewed work provided dates, faunal remains, environmental reconstruction, and nine new hominid specimens. The material was given the name Australopithecus anamensis, because of several important differences with A. afarensis that seem to distinguish it as a separate species.

An additional twelve fossil specimens from Allia Bay, on the eastern shores of Lake Turkana, has also been placed within the species anamensis along with the Kanapoi material. The strata from which this material was recovered has been well-dated with the Ar-Ar method, and there are two well-defined levels: an earlier (4.17-4.12 mya) and a later (4.1-3.9 mya) level. Material from the lower level includes the type mandible for the species (KNM-KP 29281) with an associated portion of the left temporal bone thought to be female, an almost complete maxilla (KNM-KP 29283), and a second recently discovered maxilla with parallel postcanine tooth rows. Specimens from the upper level include a partial toothless mandible (KNM-KP 29287) with a much larger canine root and a more vertically inclined symphysis than the KP 29281 female, a tibia lacking its diaphysis (KNM KP 29285), and the original distal humerus (KP 271).

Specimens from other sites such as Sibilot Hill also may be anamensis, but there is much debate on the validity of the anamensis species, since the samples are very close in morphology to afarensis. One factor that seems to separate anamensis and afarensis is the mean body weight of the male specimens. The mean of Hadar afarensis specimens is 44.6 kg, but the body weight estimates for the tibia (KP 29285) is approximately 55 kg, and approximately 58 kg for the humerus (KP 271). These weights were estimated using McHenry's predictive regression equations. This is a very small sample to draw conclusions from, but there is a difference of nearly 20% between the anamensis and afarensis samples. Dental materials seem to show that the females, however, were close to the Hadar samples, meaning that the anamensis species was fairly dimorphic.

The anamensis species seems to have been an obligate biped, as shown by the tibia and a hallux bone recovered:

• KP 29285 has a rectangual proximal surface with anterior-posterior lengthening of the proximal articulation.
• KP 29285 has concave condyles of approximately equal area (in chimpanzees one of the condyles is convex).
• Has flat larger lateral condyle.
• There is less space between tibia and fibula than in chimps.
• There is thickened cortical bone at the proximal and distal ends.
• The shaft of the tibia ia straight.
• There is a directly inferior orientation of the distal articular surface.
• A hallux (big toe) was recovered, which showed evidence for the hallucial flexors.
• A radius recovered shows that anamensis was powerfully built, but does not show evidence of weight bearing.

The dental remains show strong similarites to A. ramidus, however the Kanapoi material differs in several important ways that distinguish it as a separate species (separate from ramidus, if not also afarensis). There is a stronger adaptations to powerful masticatory forces, the postcanine teeth are larger than in ramidus, and there is absolutely and relatively thicker enamel. Details of the mandibular fossa and the surrounding region of the cranial base also differs from the Aramis material. For example, the tympanic tube does not extend as far laterally, relative to the mandibular fossa. For these reasons, the Kanapoi materials deserve a distinct species name. The dental traits of anamensis includes:

• Has an elongated, posteriorly angled mandibular symphysis.
• Has an elongated surface at the front of the mandible, behind the incisors (postincisive plane).
• A shallow palate.
• Large, elongated canines.
• Vertical maxillary canine roots.
• Strongly asymmetric P₃.
• The upper molars are broader across the mesial sides.
• There is thicker molar enamel.

Features shared with the Aramis samples include:

• An absolutely and relatively small P₄ (it is unusual in the hominids that they are smaller than P₃.
• The deciduous molars are elongated with thin enamel.
• The tooth rows are straight, parallel, and close together.
• There is a particularly small opening of the auditory meatus (within the Hadar range, but just barely).

There is some question as to whether the Kanapoi material deserves a separate species name, or whether the material should be subsumed under afarensis. The morphology is very similar, but Leakey and A. Walker give several reasons why they believe this is a new species:

• The upper canine root is bigger and less posteriorly inclined.
• The upper molars have more sloping lingual sides (but this is a very subtle difference).
• The lower molars have more sloping buccal sides (but this is not really another reason since this is codependent with the angling of the upper molars).
• The mandibular symphysis retreats more (but this is very questionable because all specimens do not have this feature, and this is a highly variable trait).

It seems fairly reliable to distinguish the Kanapoi material from A. ramidus, however, it is highly questionable that this material is a separate species from A. afarensis. This will undoubtedly be debated until more specimens are obtained and a clearer comparison between samples can be made. In any case, the similar but more primitive anatomy of anamensis relative to afarensis make it a good candidate for a precursor to afarensis. Whether a precursor species or simply part or a highly variable population through time is a matter of some debate. I personally follow the ideology that is it ok to name new species for disputed specimens, since this designation can be changed in the future if needed. As long as the genus name is held constant in these related specimens, it is ok to separate into different species, since this seems to keep study of specimens current, and they are not simply tagged with a known taxonomy and little studied.

This bibliography contains the sources of the information cited above, as well as any sources that could provide any other information on the subject. If you know of any other sources that are pertinent to A. anamensis, please e-mail me the citation in the format used below, and I will add it to the list. Any problems with information I presented above can be sent to me here. I don't want to provide misinformation, and any corrections are gladly accepted (with proper documentation of what is wrong and why, with sources). Thanks!

Coffing, K., C. Feibel, M. Leakey, and A. Walker. 1994. "Four-million-year-old hominids from east Lake Turkana, Kenya." In American Journal of Physical Anthropology, vol. 93, pp. 55-65.

Heinrich, R., M. Rose, R. Leakey, and A. Walker. 1993. "Hominid radius from the Middle Pliocene of Lake Turkana, Kenya." In American Journal of Physical Anthropology, vol. 92., no. 2, pp. 139-148.

Johanson, D., and B. Edgar. 1996. From Lucy to Language. New York: Simon and Schuster Editions.

Leakey, M. 1995. "The farthest horizon." In National Geographic Magazine, vol. 188, pp. 38-51.

Leakey, M., C. Feibel, I. McDougall, and A. Walker. 1995. "New four-million-year-old species from Kanapoi and Allia Bay, Kenya." In Nature, vol. 376, pp. 565-571.

McHenry, H. 1992. "Body size and proportions in early hominids." In American Journal of Physical Anthropology, Vol. 85, no. 2, pp. 407-431.

Patterson, B., and W. Howells. 1967. "Hominid humeral fragment from early Pleistocene of northwestern Kenya." In Science, vol. 156, pp. 64-66.

Wolpoff, M. 1999. Paleoanthropology. second edition. Boston: McGraw-Hill.