Nearly one hundred fossil specimens of A. anamensis are known from Kenya[5][6] and Ethiopia,[7] representing over twenty individuals. The first fossils of A. anamensis discovered, are dated to around 3.8 and 4.2 million years ago and were found in Kanapoi and Allia Bay in Northern Kenya.[8]
It is usually accepted that A. afarensis emerged within this lineage.[9] However, A. anamensis and A. afarensis appear to have lived side by side for at least some period of time, and it is not fully settled whether the lineage that led to extant humans emerged in A. afarensis, or directly in A. anamensis.[10][11][12]
Fossil evidence determines that Australopithecus anamensis is the earliest hominin species in the Turkana Basin,[13] but likely co-existed with afarensis towards the end of its existence.[10][14]A. anamensis and A. afarensis may be treated as a single grouping.[15]
Preliminary analysis of the sole upper cranial fossil indicates A. anamensis had a smaller cranial capacity (estimated 365-370 c.c.) than A. afarensis.[10]
^Lewis, Jason E.; Ward, Carol V.; Kimbel, William H.; Kidney, Casey L.; Brown, Frank H.; Quinn, Rhonda L.; Rowan, John; Lazagabaster, Ignacio A.; Sanders, William J.; Leakey, Maeve G.; Leakey, Louise N. (2024). "A 4.3-million-year-old Australopithecus anamensis mandible from Ileret, East Turkana, Kenya, and its paleoenvironmental context". Journal of Human Evolution. 194. 103579. doi:10.1016/j.jhevol.2024.103579.