Cape rock lobster (Jasus-lalandii) remains from South African west coast shell middens:: Preservational factors and possible bias

Cape rock lobster (Jasus lalandii) remains in South African west coast shell middens are represented by calcareous mandibles, and by fragments of exoskeleton when preservation is good. Quantification of MNIs and observations on body size of Cape rock lobsters have been based on counts and measurements on the surviving mandibles. Little is known of the importance of this resource in precolonial hunter-gatherer subsistence, and even less is known about the possible preservational bias affecting the recovery of representative quantitative data from Cape rock lobster mandibles. The latter problem is crucial to resolve in order to understand issues about coastal hunter-gatherer subsistence. Left and right mandibles are not exact mirror images of each other, with left mandibles being consistently larger and thicker than the right mandibles. Moreover, small mandibles measuring between 4.5 and 7.5 mm are much thinner and delicate than large specimens. Due to their small size, however, small mandibles can escape attrition by falling within protective spaces, such as those created under large whole shells. In order to ascertain whether or not left mandibles survive in larger number than right ones, and whether or not smaller mandibles (left and right) break more frequently than larger ones, we conducted basic statistical procedures with quantitative data (frequency and mean size of mandibles) from a variety of depositional contexts. The results show that left and right mandibles break with the same frequency, and that breakage does not bias measurements of mandibles towards the larger or smaller end of the size range. Similar studies will need to be conducted when recovering Cape rock lobster mandibles form depositional contexts different to the ones encountered in the study area.