Age and context of mid-Pliocene hominin cranium from Woranso-Mille, Ethiopia

A fossilhominin cranium was discovered in mid-Pliocene deltaic strata in the Godaya Valley of the northwestern Woranso-Mille study area in Ethiopia. Here we show that analyses of chemically correlated volcanic layers and the palaeomagnetic stratigraphy, combined with Bayesian modelling of dated tuffs, yield an age range of 3.804 ± 0.013 to 3.777 ± 0.014 million years old (mean ± 1σ) for the deltaic strata and the fossilsthat they contain. We also document deposits of a perennial lake beneath the deltaic sequence. Mammalian fossilsassociated with the cranium represent taxa that were widespread at the time and data from botanical remains indicate that the vegetation in the lake and delta catchment was predominantly dry shrublandwith varying proportions of grassland, wetland and riparian forest. In addition, we report high rates of sediment accumulation and depositional features that are typical of a steep topographic relief and differ from younger Woranso-Mille fossillocalities, reflecting the influence of active rift processes on the palaeolandscape. Two related studies describe a newly discovered cranium of Australopithecus anamensis, the environment in which this hominin would have lived approximately 3.8 million years ago and how it is related to Australopithecus afarensis.