Phylogeny of earlyAustralopithecus: new fossil evidence from the Woranso-Mille (central Afar, Ethiopia)

Abstract

The earliest evidence ofAustralopithecusgoes back toca4.2 Ma with the first recorded appearance ofAustralopithecus ‘anamensis’at Kanapoi, Kenya.Australopithecus afarensisis well documented between 3.6 and 3.0 Ma mainly from deposits at Laetoli (Tanzania) and Hadar (Ethiopia). The phylogenetic relationship of these two ‘species’ is hypothesized as ancestor–descendant. However, the lack of fossil evidence from the time between 3.6 and 3.9 Ma has been one of its weakest points. Recent fieldwork in the Woranso-Mille study area in the Afar region of Ethiopia has yielded fossil hominids dated between 3.6 and 3.8 Ma. These new fossils play a significant role in testing the proposed relationship betweenAu. anamensisandAu. afarensis. The Woranso-Mille hominids (3.6–3.8 Ma) show a mosaic of primitive, predominantlyAu. anamensis-like, and some derived (Au. afarensis-like) dentognathic features. Furthermore, they show that, as currently known, there are no discrete and functionally significant anatomical differences betweenAu. anamensisandAu. afarensis. Based on the currently available evidence, it appears that there is no compelling evidence to falsify the hypothesis of ‘chronospecies pair’ or ancestor–descendant relationship betweenAu. anamensisandAu. afarensis. Most importantly, however, the temporally and morphologically intermediate Woranso-Mille hominids indicate that the species namesAu. afarensisandAu. anamensisdo not refer to two real species, but rather to earlier and later representatives of a single phyletically evolving lineage. However, if retaining these two names is necessary for communication purposes, the Woranso-Mille hominids are best referred to asAu. anamensisbased on new dentognathic evidence.