Assessing the effects of fluvial abrasion on bone surface modifications using high-resolution 3-D scanning

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Stone tool cut marks and carnivore tooth marks on fossil bones are invaluable traces of the feeding behavior and ecology of our ancestors. Recent research has focused on quantifying the micromorphology of experimentally created cut and tooth marks using high-resolution 3-D scanning technology with the goal of improving the reliability and accuracy of interpretations that are based on these feeding traces. However, to apply these experimental data in the identification and interpretation of bone surface modifications on fossil bones, the effect of post-depositional processes on the micromorphology of feeding traces must be known. Previous research has shown that fluvial abrasion has a substantial impact on the qualitative criteria that are used to identify cut marks, but the specific effect of hydraulic transport and abrasion on quantifiable attributes of bone surface modifications is completely unknown.The objective of this research is to understand the effects of fluvial abrasion on the micromorphology of cut marks and mammalian carnivore tooth marks using high-resolution 3-D data. An experimental study was undertaken by tumbling cattle and deer bones in a rock tumbler filled with sand and water to simulate the effects of fluvial abrasion on the bone surface modifications. Variables were measured using qualitative (visual observation of rounding and polishing of the bone surfaces, and the effect of these processes on the potential identifiability of cut and tooth marks) and quantitative (surface area, volume, maximum depth, mean depth, maximum length, maximum width, roughness, angle, and radius of the marks) criteria. The 3-D data from cut and tooth marks was collected using a white-light confocal profilometer and analyzed with specialized surface metrology software. Analyses of both qualitative and quantitative data indicate that fluvial abrasion has a greater effect on cut marks than tooth marks, suggesting that the frequency of cut marks could be underestimated relative to carnivore tooth marks in archaeological assemblages preserved in fluvial environments. This could affect interpretations of hominin feeding behavior based on the abundance of bone surface modifications when relying on qualitative methods alone. However, 98.6% of marks were identified correctly after tumbling when using multivariate quantitative methods of analysis bolstering the need for applying these methods in the interpretation of bone surface modifications on fossil specimens.