Dental data challenge the ubiquitous presence of Homo in the Cradle of Humankind

The origins of Homo, as well as the diversity and biogeographic distribution of early Homo species remain critical outstanding issues in paleoanthropology. Debates about the recognition of early Homo, first appearance dates, and taxonomic diversity within Homo are particularly important for determining the role that southern African taxa may have played in the origins of the genus. The correct identification of Homo remains also has implications for reconstructing phylogenetic relationships between species of Australopithecus and Paranthropus, and the links between early Homo species and H. erectus. We use microcomputed tomography and landmarkfree deformation-based three-dimensional geometric morphometrics to extract taxonomically informative data from the internal structure of postcanine teeth attributed to Early Pleistocene Homo in the southern African hominin-bearing sites of Sterkfontein, Swartkrans, Drimolen and Kromdraai B. Our results indicate that from our sample of 23 specimens, only four are unambiguously attributed to Homo, three of them coming from Swartkrans Member 1 (SK 27, SK 847 and SKX 21204) and one from Sterkfontein (Sts 9). Three other specimens from Sterkfontein (StW 80-81, SE 1508 and StW 669) approximate the Homo condition in terms of overall enameldentine junction shape, but retain Australopithecus-like dental traits, and their generic status remains unclear. The other specimens, including SK 15, present a dominant australopith dental signature. In light of these results, previous dietary and ecological interpretations can be reevaluated, showing that the geochemical signal of one tooth from Kromdraai (KB 5223) and two from Swartkrans (SK 96 and SKX 268) is consistent with that of australopiths.