Aquatic bone taphonomy: forensic and archaeological implications for the interpretation of submerged bone

Abstract

There is currently an incomplete understanding of the effects that aquatic processes have on skeletal material, and consequently the interpretation of water-submerged remains presents a number of challenges to archaeologists and forensic practitioners. Accurate interpretations of the conditions which cause diagnostic diagenetic changes to material are not just important for reconstructing post-depositional environments, processes and durations, but are also vital in ensuring that any data recovered from bone are not incorrectly interpreted due to information loss and modification. This thesis therefore addresses the paucity in data concerning early postdepositional modifications in submerged bone, by exploring different methods and analyses that facilitate more accurate interpretations of bones’ aquatic diagenetic and taphonomic pathways. A number of experimental and actualistic bone taphonomy studies are presented and discussed. A series of laboratory flume-based experiments demonstrate the utility of quantitative analysis of sediment-induced micro- abrasion on bone surfaces. SEM imaging allowed quantitative and qualitative distinctions to be made concerning the sediment size class that the bone was abraded by. Changes in sediment grain size, duration of exposure to abrasion, sphericity of the abrasive, and abrasive force are identified as the strongest rate-limiting factors controlling micro-abrasion propagation. Through this data it is suggested that a quantitative approach to analysing abrasion on bone retrieved from water has potential to establish remains’ submersion times and transport pathways with a higher degree of resolution than previously possible. The use of laser scanning for quantitatively recording sediment abrasion on submerged bone is also explored. Point cloud analysis was carried out, and it is shown that laser scanning can be used to accurately record abrasion on submerged bone at a resolution not possible through gross morphological assessment. It is therefore suggested that this quantitative approach facilitates an improved assessment of abrasive changes recorded on bone in experimental and actualistic taphonomy studies. Finally, a series of early-post-depositional monitoring studies were conducted in field and laboratory-based settings to assess both predictability and rates of diagenetic change as they relate to different spatio-temporal parameters of submersion. A suite of physicochemical changes in bone, recorded using gross morphological observations, histological assessments of bone microstructure, DNA analysis, FTIR-ATR analysis of bones’ mineral and organic constituents, quantitative measures of colour change using VSC analysis, and XRF analysis of bones’ elemental compositions, are discussed. The key findings of this study are that microbial modification in submerged osseous tissue can progress rapidly upon deposition in water and have the ability to propagate into cortical tissue, which may impact on the ability of remains to survive over archaeological and palaeontological time periods. Elemental exchange rates in submerged bone are identified as the most consistent markers of post-depositional change at both site-specific and broader scales. Remains that were constantly buried in bottom sediments and exhibit good gross morphological and histological integrity displayed notably consistent elemental uptake and depletion rates, which suggests they have utility for determining remains’ submersion times and locations. DNA degradation is shown to be rapid in submerged bone due to the effects of hydrolysis. It is also indicated that remains which experienced burial and exhibit limited microstructural changes are likely to show better retention of residual biomolecules and are therefore favourable to target for DNA analysis. This thesis concludes that a quantitative approach to recording both intrinsic and extrinsic variables related to bone diagenesis is advantageous for understanding taphonomic effect, cause and duration, and should therefore be adopted in future studies. In addition, this research provides a good fundamental basis concerning the occurrence and progression of different diagenetic changes in water-submerged remains, on which additional studies can build.

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ORCID for Charlotte Thompson: orcid.org/0000-0003-1105-6838

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