Australopithecus anamensis is a hominin species that lived roughly between 4.3 and 3.8 million years ago, and is the oldest known Australopithecus species.

Nearly 100 fossil specimens of A. anamensis are known from Kenya and Ethiopia, representing over 20 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.

A. afarensis is normally accepted to have emerged within this lineage. However, A. anamensis and A. afarensis appear to have lived side-by-side for at least some period of time, and whether the lineage that led to extant humans emerged in A. afarensis, or directly in A. anamensis is not fully settled. 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 cm³) than A. afarensis.

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