Marc Dickinson

Amino acid racemisation dating of mammalian enamel: a British Elephantidae geochronology

Marc Dickinson §; Adrian Lister£; Kirsty Penkman §

£ The Natural History Museum, London; § Department of Chemistry, University of York, York, YO10 5DD, UK

Establishing robust chronologies is imperative for our understanding of a range of palaeontological enquiries. Directly dating mammalian remains older than the limit of radiocarbon dating (~50 ka) is extremely challenging, but recent advances in amino acid racemisation (AAR) geochronology, which uses the predictable breakdown of proteins and amino acids, has been a powerful tool for Pleistocene age estimation (back to ~2.5 Ma) of a wide variety of calcium carbonate (CaCO3) based biominerals. By targeting a proteinaceous fraction found within the crystalline structure of biominerals (the intra-crystalline fraction), the difficulties associated with contamination, leaching and environmental influences are circumvented. We have assessed the suitability of tooth enamel for intra-crystalline protein decomposition (IcPD) dating by testing both the protein breakdown and the intrinsic properties of the inorganic crystal structure of enamel. This has allowed us to build an AAR geochronology based on Elephantidae enamel, with an age range that shows the technique successfully dates material from the UK up to Late Pliocene in age. It is therefore now possible to provide direct age estimation for unknown age Elephantidae material from the same temperature region (likely to be Northern Europe). Enamel AAR has the potential to be expanded to a range of mammalian species and can be developed for additional geographic regions. The focus of this framework has been on Quaternary age samples, but due to the slower breakdown of the enamel proteins, the dating range of this method may extend much further back in time.