Geochemical chronologies in Paranthropus robustus teeth inform habitat and life histories

Radiogenic strontium isotopes (⁸⁷Sr/⁸⁶Sr) and the alkaline earth ratios (AERs) Sr/Ca and Ba/Ca in fossil dental enamel can inform the habitat, residence and life histories of early hominins recovered from the Pleistocene cradle-of-humankind sites of Gauteng, South Africa. Key questions, which may be addressed with these indices, are the relative exploitation of wet versus dry botanic regimes and whether early hominins dispersed in a manner similar to that of chimpanzees (characterized by male philopatry and female dispersal at puberty) or to that of humans (who are not so characterized). Here we developed 28 new dental chronologies in 20 Paranthropus robustus teeth from Swartkrans and Kromdraai. Resulting geochemical time series demonstrate that, while maternal ⁸⁷Sr/⁸⁶Sr in earlier-forming teeth varies widely, third molar ⁸⁷Sr/⁸⁶Sr, derived from postweaning solid foods, progressively converges to 0.7306 ± 0.0035 (± 2 s.d.), which we express as the local isotopically delineated exploitation area (LIDEA). The spatial resolution of LIDEA is determined using a bioavailable ⁸⁷Sr/⁸⁶Sr isoscape. In this environmental context, we interpret LIDEA as a quantifiable signal indicating eurytopy (generalization), with some 30% of Sr deriving from riparian woodland habitats. With regard to residence, many individuals arrived at the site after second molar mineralization, while some matured locally, demonstrating both male and female dispersal as well as lifelong local residence. Analysis of both ⁸⁷Sr/⁸⁶Sr and the AERs further highlights concomitant patterns, as well as numerous periodicities that may be related to resource depletion, seasonality or lunar cycles.