Radiocarbon dating of human remains from the late Neolithic dolmen of Oberbipp (Switzerland). Clarifying the chronology and sequences of burials

Undisturbed collective megalithic burials are extremely rare. The dolmen of Oberbipp provides a unique opportunity for multidisciplinary research. Morphological analysis indicate at least 42 individuals buried in the grave chamber. Using archaeology alone it was not possible to determine different occupation periods of the inhumations. Neolithic communities often reused dolmen over centuries, therefore radiocarbon dating might be able to solve this question. Fragments of the same bone element (right femora) were analyzed by two (in some cases three) different laboratories to date all inhumations individually. This study had three aims: a) determine the total occupation time of the dolmen; b) evaluate the sequence of the burials; c) compare the results of the same skeletal element from different laboratories. In total, 79 radiocarbon results from three different laboratories of the right femora (n=32) are available. The broad application of radiocarbon dating allowed the determination of two occupation periods within the burial: The majority of the femora (n=26) date between 3350-2950BCE, but three samples are from a younger period (2900-2650BCE). The comparison between radiocarbon dates obtained in different laboratories for the same sample showed little variation and only a few samples differed substantially. Our sampling strategy indicates the necessity for archaeological settings such as multiple burials to include large serial radiocarbon measurements to ensure that all occupation phases are uncovered. In addition, our data indicate that dating at different laboratories should be included in the sampling process to guarantee that the interpretation is based on the best available data. Even though the overall concordance across the laborites was good, little variation could lead to a different interpretation of a site. In future it should also be considered to include other bioarchaeological methods such as aDNA analysis in combination with radiocarbon dating to overcome problems related to plateaus of the calibration curve.