THE Hadar Formation in Ethiopia is a prolific source of Pliocene Hominidae attributed to the species Australopithecus afarensis1. Since 1990, three seasons of field work have contributed 53 new specimens to the hominid inventory from Hadar, including the first fairly complete adult skull. Ranging from 3.0 to 3.4 million years in age (Fig. 1)2-4 , the new specimens bear on key debates in hominid palaeontology, including the taxonomic implications of sample variation and the reconstruction of locomotor behaviour. They confirm the taxonomic unity of A. afarensis and constitute the largest body of evidence for about 0.9 million years of stasis in the earliest known hominid species.