The amino acid and stable isotope biogeochemistry of elephant bird (Aepyornis) eggshells from southern Madagascar

A diverse suite of animals became extinct on Madagascar during the Late Holocene. As observed on landmasses elsewhere, the extinction process broadly coincided with the arrival of people. Our research on the amino acid racemisation and the carbon and oxygen isotope biogeochemistry of elephant bird (Aepyornis) eggshells from southern Madagascar refines models that attempt to explain the extinction process. A correlation between the extent of isoleucine epimerisation (aIle/Ile) and radiocarbon age of eggshells allows aIle/Ile to serve as a proxy for eggshell age. The aIle/Ile values indicate the majority (87%) of eggshells in this study are Holocene, with the remainder representing Pleistocene Aepyornis populations, and that further amino acid analyses would help to constrain the timing of Aepyornis extinction. Carbon isotope ratios in the organic and calcite fractions of eggshells indicate that Aepyornis primarily browsed C3 vegetation. Oxygen isotope values are more negative and less variable than in eggshells of ostriches living in semi-arid environments, suggesting that Aepyornis populations relied upon groundwater-fed coastal wetlands for their drinking water. The isotope results require that the changing abundances of C3 vegetation and groundwater-fed watering points be considered in models that aim to understand the extinction of Aepyornis in southern Madagascar.