Diagenesis of bone from Border Cave: Implications for the age of the Border Cave hominids

Hominids from the site of Border Cave purportedly provide direct evidence for the early emergence of anatomically modern humans (AMH) in Southern Africa. ESR dating of Border Cave faunal enamel has confirmed the antiquity of the sediments, although questions persist regarding the provenience of the hominid specimens. Here we establish that, at Border Cave as elsewhere, bone mineral crystallinity, measured as the infrared (IR) splitting factor (SF), distinguishes between contemporary and recent bones on the one hand, from Middle Stone Age (MSA) bones on the other. Two hominid postcranial bones recovered in 1987 from a slumped profile, having essentially no provenience, are shown to have crystallinity indices consistent with the MSA fauna, while two of the purportedly ancient AMH specimens (BC3 and BC5) have values consistent with recent fauna. We conclude that BC3 and BC5 may be considerably younger than the sediments from which they were recovered. (C) 1996 Academic Press Limited