Zooarchaeology in Practice by Christina M. Giovas & Michelle J. LeFebvre

Author:Christina M. Giovas & Michelle J. LeFebvre
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

8.6 Conclusions

A great number of factors can affect shell preservation. Some are intrinsic to each species (robustness), and many others relate to taphonomic process before and after deposition . Among the latter, chemical weathering from exposure to the elements and life forms, burning, and intensity of site usage are the most important. The method for quantifying shell fragmentation presented here is probably less influenced by chemical weathering than the methods relying on sieving through stacked meshes because weight can be lost due to a number of taphonomic processes. Black mussel hinges remain attached to prismatic bands even when the shell is very chalky, although the extent of this remains to be quantified. This method is also less time consuming as indices can be calculated with data that is routinely gathered for MNI calculations, and counting or weighing shell fragments is not necessary.

When levels of burning, matrix constitution, and species composition do not vary significantly between stratigraphic units, shell fragmentation appears to be affected mainly by intra-site settlement patterns. Black mussel shells preserve better when deposition rates are faster as a result of longer occupation, and suffer greater fragmentation when deposition rates are slower resulting from shorter visits. When visits decline to such an extent that a significant gap in site occupation (several centuries) is obvious, then shell fragmentation is exacerbated as a result of the protracted exposure of shell remains to the weathering action of the natural elements. Following the methodology outlined here, additional studies on black mussel shell fragmentation at other sites might well show the same causative association. If so, then fragmentation indices as calculated here could then be used as effective tools in reconstructing patterns of site usage. Hence, this method not only would save time and resources for quantifying shell fragmentation, but would also contribute towards a better understanding of intra-site settlement patterns and, by extension, of those at a regional scale.

The basic rationale that sustains this alternative method can be applied to other South African species and to those common in shell middens elsewhere in the world. The success of this exercise would depend on the choice of the species to study as obtaining a continuous, rather than discrete, range of FI values would be best for evaluating shell preservation on a quantitative basis. Most importantly, shell robustness and architecture of the diagnostic and countable elements and their contiguous shell material would need to be taken into account when applying this method to other species.

Comparability of methods is always desirable in archaeology as this allows for making stronger cases and for assessing assemblages against others with potentially different faunal composition and depositional histories. Consequently, future work on shell taphonomy would certainly benefit from experimental studies and from laboratory analyses where different methods for evaluating shell fragmentation are applied jointly to a number of assemblages and results compared.

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