M.A. Theses: Beverley Alistair Nicholson, 1981

An Investigation of the Potential of Freshwater Mussels As Seasonal Indicators in Archaeological Sites.

Evidence has been presented in the palaeontological literature that marine bivalves preserve in their calcareous shells a record of the environmental events and astronomical periodicities which affect their metabolic processes. The most prominent feature of this record is the external growth ring initiated by the annual decline in the mean temperature of the environment. It has been shown that small scale events based on circadian and tidal rhythms are also recorded. Recent articles in archaeological journals have suggested that this information forms the basis for estimating the season of occupation of many archaeological sites.

In order to evaluate the potential of freshwater mussels as seasonal indicators in archaeological sites, a modern sample of live mussels was sequentially gathered in the Canadian Interior Basin, together with pertinent environmental information. The sample was analysed using a variety of the methods which have been proposed in the literature. To evaluate macroscopic techniques of estimating seasonality, a random sample of Lampsilis siliquoidea valves was drawn from the study population. Using this sample, a series of independent observer tests were made which indicated that macroscopic techniques of analysis for the estimation of seasonality were highly unreliable. To evaluate microscopic techniques, radial shell sections were prepared as acetate peel replicas and thin sections for microstructural analysis by means of the scanning electron microscope (SEM) and a binocular light microscope Stained thin sections, examined with transmitted light, were found to be the most satisfactory technique from the standpoints of consistent results, ease of study, and maximum yield of information.

While the variability of the specimens indicated that a moderately large sample is required, the results of the thin section analysis indicated that seasonality estimates may be derived with reasonable accuracy from the shells of freshwater mussels. The season in which the mussels died may be estimated by means of averages calculated from the counts of microincrements contained in the final macroincrement deposited on the ventral edge of the shells in a sample. The results of this research confirm the hypothesis that the patterns of shell deposition in freshwater mussels are principally the result of metabolic reactions to environmental variables and form a reliable basis for seasonality estimates.