Article: The interpretation of size-frequency distributions in molluscan death assemblages

It has been widely assumed that water currents play a major role in determining the shape of the size-frequency distributions of molluscan and brachiopod shells in death assemblages, by the selective removal of small-size grades. To test this assumption, the commonest bivalve and gastropod species in two transported death assemblages, one fossil and one forming at present, have been subjected to size-frequency analysis. The interaction of varying growth and mortality rates among living bivalves is discussed and the results of experimental work on shell fragmentation presented. It is concluded that the size-frequency distributions of the death assemblages under consideration primarily reflect growth and mortality rates, modified somewhat by the selective destruction of smaller shells. The invocation of size sorting appears to be unnecessary, and this postulated process has still to be demonstrated as a significant factor in controlling the shape of size-frequency distributions.