Australopithecus anamensis is a hominin species that lived approximately between 4.2 and 3.8 million years ago and is the oldest known Australopithecus species. Nearly one hundred fossil specimens are known from Kenya and Ethiopia, representing over 20 individuals. It is usually accepted that A. afarensis emerged within this lineage. However, A. anamensis and A. afarensis appear to have lived side-by-side, and it is not fully settled whether the lineage that led to extant humans emerged in A. afarensis, or directly in A. anamensis. 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. A. Anamensis and A. Afarensis may be treated as a single grouping. Preliminary analysis of the sole upper cranial fossil indicates A. anamensis had a smaller cranial capacity (estimated 365-370 c.c.) than A. afarensis. A. anamensis is the earliest known species of Australopithecus and the least studied because of lack of skeletal findings. The first fossils of the A. anamensis are dated to around 3.8 and 4.2 million years ago and were found in Kanapoi and Allia Bay in Northern Kenya. They are the earliest Australopithecus species, living during the Plio-Pleistocene era.