Making numbers count: Beyond minimum numbers of individuals (MNI) for the quantification of mollusc assemblages from shell matrix sites

Abstract

Abstract Inferences on the relative importance of marine mollusc taxa from archaeological assemblages are usually based on counts of minimum numbers of individuals (MNI) for each taxon present. The exact procedure adopted for estimating MNI will vary according to a range of factors, including the structural properties of the shells of various taxa, the specific characteristics of the shell matrix site and the degree of preservation of the taxa present. This is illustrated by reference to the assemblages of marine molluscs from the shell matrix site of Culverwell, southern Britain. Various indices of quantification are considered (crude MNI, standardized MNI, weight of shell, meat-yield adjusted MNI, and rates of incorporation of shell into the site) and the applicability of each is examined in relation to a range of research objectives. Our study shows that issues relating to counting MNIs are not only taxon-, but also site-, specific. Even when MNI counts are accurate estimates of shells surviving at and recovered from a site, they are not necessarily reliable estimates of the relative dietary importance of the quantified taxa. We suggest an additional means of addressing such methodological challenges, based on meat yields derived from studies of living molluscs of taxa encountered archaeologically. The Culverwell case study is an example of how sampling, recovery and quantification procedures need to be adapted to the characteristics of the site and the preservation characteristics of the mollusc assemblages, and shows the difficulty of gaining fully standardized MNI counts across all the principal taxa. Moreover, counting MNIs will not always give accurate estimates of the relative importance of mollusc taxa in past human subsistence. Archaeomalacological investigations of past human diets should, we suggest, include studies of the living animals as well as of the shells of the species encountered in the archaeological record. Actualistic approaches, by permitting more nuanced interpretations of marine molluscs from archaeological sites, are likely to be of value to many archaeomalacological research objectives.