Impact of a recent wildfire on tortoises at Cape Point, South Africa, and implications for the interpretation of heated bones in the archaeological record

Heat-altered bones are a common occurrence in the archaeological record, and their analysis can provide detailed insights into past fire use behaviors and subsistence strategies. Heat-altered bones, however, may also result from natural fire events such as wildfires that are unrelated to human activity. We currently lack robust reference materials from natural fire events, analyzed using the same methodological approaches as we apply them to archaeological assemblages, that can be used to differentiate between natural and anthropogenic origins of heated materials. Here, we studied an assemblage of 50 tortoises that perished in a brushfire in Cape Point, South Africa. We used a combination of (1) zooarchaeological assessments of heating pattern and (2) infrared spectroscopy including a heating experiment to reconstruct heating temperatures with the aim to document the fire impact on the tortoise remains. For both approaches, we used statistical models to develop and test predictions that can also be applied to archaeological material. Our analyses suggest a quickly moving and low temperature brushfire in the study region with a generally low and superficial heating impact on the tortoise remains. However, we also observed several high-temperature alterations with calcination and speculate that naturally occurring fuel sources controlled the severity of the fire impact. The evidence of heating on the tortoise was unpatterned. We conclude that temperature alone presents a low confidence deciding factor between wildfires and campfires while skeletal heating pattern, in concert with other contextual analysis, may be able to facilitate this distinction with more localized heating signatures for campfires.