Bone Fractures under the Microscope. An Experimental Approach to Mid-Upper Paleolithic Faunal Remains

Abstract

Bone fragmentation results from different natural processes or various activities employed by several taphonomic agents. However, it may also represent direct evidence of deliberate human activity connected to the exploitation of animal resources throughout the Paleolithic period. Extensive long mammal bone fragmentation research resulted in last decades into description of individual fracture characteristics reflecting the background of fragmentation process (Johnson 1985; Outram 2001). The features combine macroscopic traits such as angle, an outline, and surface texture of the fracture. However, as the experimental works show, the response of bone on a gross scale is in great extent given by microstructure and its state of preservation directly correlating with the biomechanical properties (Currey 2012; Gifford-Gonzales 2018). The paper aims on testing (1) whether the microscopic features correlate with described macroscale differences or even (2) are able to distinguish features with macroscopic overlaps but of different origin. We have thus tested and applied two microscopic methods on two experimental assemblages with documented fragmentation conditions. By the scanning electron microscopy (SEM) we observed irregularities and micro-fractures in bone fracture surface (FS). They proved to be in certain aspect specific for a given state of bone preservation. Transmitted light microscopy mapped the abundance of micro-cracking, its characteristic features in relation to bone preservation and specific way of fragmentation. The histological thin-sections (HTS) revealed a variety of micro-cracking penetrating the FS, but they did not prove any differentiating pattern among observed experimental sets. A range of different surface profiles was documented, the profile morphology seems to be characteristic for individual bone preservation states. If compared to macroscopic method (FFI), the study of microscopic features in their presented extent did not allow us to differentiate further between fractures. Finally, we undertook an example application of the macroscopic fracture analysis on settlement areas from the Gravettian site Pavlov I (Czech Republic) and we discuss the potential of suggested micro-methods in taphonomic analysis dealing with animal body manipulation and exploitation.