Originally discovered in 1965 by Bryan Patterson's expedition from Harvard University, A. anamensis was not explicitly identified until 1994 by Maeve Leakey when work on the site finally began. One of the earliest human ancestors, this member of the Australopithecus genus is closely related in particular to A. afarensis.

The sites were in Kanapoi and Allia Bay in North Kenya, west of Lake Turkana. Nine fossils were recovered from Kanapoi, including a distal end of a humerus (KNM-KP 271), and twelve fossils were found at Allia Bay. Among those found were upper and lower jaws, cranial fragments and the upper and lower parts of a tibia.

Named "anamensis" from the word "anam" meaning "lake" in the local Turkana language, there was much contestation over how to classify the newly discovered species. It was eventually decided that it needed a separate classification due to certain distinctive differences between it and A. afarensis.

The fossils recovered are dated at approximately 4 million years, and the tibia found indicates that A. anamensis was considerably larger than A. ramidus and A. afarensis. Weight is estimated to be between 46 and 55 kilogram (about 100 to 120 pounds); the species was bipedal, pushing back the earliest bipedal human ancestors by about half a million years. According to Leakey et al., the team that did the majority of the work on the site, the following provides evidence for bipedalism:

"... rectangular proximal surface with anterior/posterior lengthening of the articular surfaces, condyles both concave and of roughly equal area, expanded metaphyseal bone, probably small fibular articulation, very straight shaft in those parts preserved, and a distal articular surface that faces directly inferiorly." 1

Other characteristics which make A. anamensis distinctive is the small external acoustic meatus, the parallel teeth which are set close together with large canines, wide upper molars, and a distal humerus with a cortex that encloses the small medullary cavity. A. anamensis is differentiated from A. afarensis by the large upper canine roots along with other moderate facial variations. It is distinguished from A. ramidus by the thicker enamel on the teeth and other dental differences.

1 Maeve G. Leakey, Craig S. Feibel, Ian McDougall and Alan Walker. 1995. "New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya". Nature 376:565-571.

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