Decoding Bone Bioerosion: a microCT and SEM study of Spanish Civil War lime graves

Bacterial bioerosion is a key taphonomic process affecting bone remains in diverse environments This study presents the anthropological and taphonomic study of two clandestine lime graves from the Spanish Civil War (1936–1939). We could demonstrate that lime does not prevent bacterial action during decomposition, and does not cause bodies to disappear, but dehydrates bone tissue. Not all the cross-sections prepared for SEM analysis consistently revealed microbial attack due to certain heterogenous intensity and distribution across the entire skeletal element and the osseous matrix of some the specimens. One apparent cause of the bacterial absence could have been the lime used in these burials. However, microCT confirmed bacterial attack even in areas externally appearing unaffected. In addition, the distribution and location of the bacterial attack observed by microCT, bioerosion dispersal in the bodies in the context of the burial reinforce the endogenous origin of bacteria. These findings emphasize the importance of applying non-invasive imaging techniques in forensic and archaeological contexts for assessing bone-diagenetic processes. While optical and scanning electron microscopy (SEM) is commonly used to assess bacterial bioerosion, microCT analyses has proven essential for identifying and recognizing bacterial activity, which is relevant to interpret the burial environment.