New hominin genus from eastern Africa shows diverse middle Pliocene lineages

Most interpretations of early hominin phylogeny recognize a single early to middle Pliocene ancestral lineage, best represented by Australopithecus af arensis, which gave rise to a radiation of taxa in the late Pliocene. Here we report on new fossils discovered west of Lake Turkana, Kenya, which diff er markedly from those of contemporary A. afarensis, indicating that homini n taxonomic diversity extended back, well into the middle Pliocene. A 3.5 M yr-old cranium, showing a unique combination of derived facial and primitiv e neurocranial features, is assigned to a new genus of hominin. These findi ngs point to an early diet-driven adaptive radiation, provide new insight o n the association of hominin craniodental features, and have implications f or our understanding of Plio-Pleistocene hominin phylogeny.