Date Published: October 3, 2018
Publisher: Public Library of Science
Author(s): Hege Ingjerd Hollund, Malou Blank, Karl-Göran Sjögren, Luca Bondioli.
This study investigates possible variation in post-mortem histories during the Neolithic period in southwestern Sweden based on microscopic studies of human bone. Numerous megalithic graves were built in this region and good preservation conditions have left a rich skeletal record. After more than a hundred years of research, it is still a controversy whether or not these skeletal assemblages were the result of primary burials, or ossuaries where skeletonized remains were deposited. In this study we apply histological analysis to obtain insights into post-mortem histories and taphonomic processes affecting the human remains, potentially including funerary rituals. This type of analysis records the condition and traces of degradation found in skeletal material at a microscopic level. Human skeletal material from four different megalithic tombs in the Falbygden area has been sampled and analysed by thin-section light microscopy, and by scanning electron microscopy. The results of the study provide evidence of variation and changes in burial conditions for skeletal remains from the different graves, also for remains from the same grave. Extent of bioerosion varied, from extensive to moderate/arrested, to none. Bone samples from the same graves also differed in the type of staining and mineral inclusions, showing that the non-bioeroded samples relatively early post-mortem must have experienced an anoxic environment, and later a change to an aerated environment. This could be taken as an indication of primary burial somewhere else, but more likely reflect a special micro-environment occurring temporarily in some graves and parts of graves after the tombs were filled with soil and sealed by roof slabs. The study illustrates the usefulness of bone histological analysis in the reconstruction of post-mortem histories, revealing variations not discernible at macro-level that may aid in the interpretations of funerary rituals. However, the results also highlight the issues of equifinality. Based on current data and knowledge, several scenarios are possible. Further histotaphonomic work is advisable, including archaeological remains from megalithic tombs, and bones from taphonomic experiments.
Far from being simply dead and buried, many prehistoric deceased bodies are likely to have gone through a variety of different funerary rituals before becoming part of the archaeological record, most of which will remain unknown to us. The skeletal assemblages of megalithic graves are intriguing examples of this, and the exact nature of mortuary practices carried out in connection with burials in the graves has been the subject of long-lasting debate [1, 2–8]. Still, there is no consensus in how to interpret the remains in these graves. In Scandinavia, the megalithic graves have been described as ossuaries where dismemberment and deposition of defleshed human bodies were practiced [4, 5, 9, 10], while other researchers have suggested that they were predominantly used for primary successive burials [1, 7, 11–14].
A total of 21 individuals from four Falbygden graves were radiocarbon dated and sampled for histological analysis. The aim of the sampling strategy was to include individuals from different parts and levels of the graves, and different time periods, although the majority date to the Late Neolithic II period. The material originates from two Middle Neolithic passage graves, Falköping Östra 1 (FÖ1) and Gökhem 94 (GH94:1), and two Late Neolithic gallery graves, Torbjörntorp 18 (TB18), and 31 (TB31) (Figs 2 and 3, Table 1). In addition, the mandible of a wild cat from TB18 was also sampled. Further details on the graves, sites and skeletal assemblages may be found in Table 1 and in the supporting information (S1 File and S2 Table).
The results of the histological analysis are summarized in Table 3.
The results of the histological analysis show that there is variation in diagenetic patterns and degrees of preservation within and between the graves, and across time periods. Samples displayed either extensive or arrested bioerosion, or no bioerosion, and different combinations of these patterns were apparent in the different graves. As the most common faith of archaeological bone is extensive bioerosion, and since a previous histological analysis had shown medium to extensive bioerosion in all samples from GH94:1, it was surprising to observe that the majority of analysed samples from grave TB18, and one from FÖ1, were not bioeroded, A previous study recording bioerosion of bones in the Rössberga tomb  showed bones displaying all three patterns (extensive, arrested, no/negligible bioerosion). In our study, we furthermore recorded variation in the extent of microcracking, etching as well as extent and type of staining and inclusions across the analysed assemblage, which showed a relationship with the pattern of bioerosion. The bones displayed one out of three overall diagenetic patterns:
This histotaphonomic investigation of a bone assemblage from Neolithic megalithic graves in southwestern Sweden has revealed both diachronic and synchronic variation in post-mortem histories, based on different diagenetic patterns observed. Dark stains and inclusions of manganese oxides were restricted to bones with no- or arrested bioerosion, showing that these bones had temporarily experienced an anoxic burial environment. Both stained and unstained bones were found in two of the graves, whereas all the bones from the late Neolithic passage grave TB18 were stained, and most were not bioeroded. Possible scenarios to explain this include temporary burial in an anoxic environment such as a peat bog, but is perhaps more likely related to localized and temporary variation in redox potential within and between tombs due to factors such as depth, differential sediments and/or build-up of organic material. Some or all of the manganese precipitates may be microbially mediated, suggesting that the precipitation occurred when soft tissue was still present. This opens up the possibility that the stained bones were somehow mummified, naturally or artificially, and in that way gave rise to special microbial communities and micro-environments within the tombs different to those of presumably skeletonised remains. The extensively bioeroded bones with no manganese precipitates must have experienced an oxygenated environment throughout the post-mortem period. It is uncertain, however, whether or not the extensive bioerosion observed could have occurred during putrefaction in the open tomb, or started/continued after the skeletonised bones were buried.