Calcium isotopic ecology of Turkana Basin hominins.

Diet is a major driver of hominin evolution, but most of the geochemical evidence relies on carbon isotopes (δC). Here, we report enamel stable calcium isotope (δCa) values against δC values for several hominins and co-existing primates in the Turkana Basin area, circa 4 to 2 Ma. Australopithecus anamensis clusters with mammal browsers, Kenyanthropus platyops is distinct from A. anamensis in foraging into more open environments and the coexisting Theropithecus brumpti encompasses both the grazer and omnivore/carnivore domains. Early Homo is remarkable for its wide distribution in δCa values, possibly reflecting omnivorous and opportunistic preferences. Paranthropus boisei is uniquely distributed in the δC versus δCa iso-space being distinct from all other hominins from the Turkana Basin area as well as from the co-existing Theropithecus oswaldi. Several hypotheses are explored to discuss the unique δCa values of Paranthropus boisei including significant differences observed with δCa values recently reported for P. robustus from South Africa, questioning the monophyly of this genus.