Middle Stone Age (MSA; 250,000 to 50,000 years ago) and Later Stone Age (LSA; 50,000 years ago to historic times) archaeological sites along the coast of South Africa frequently preserve the remains of marine shellfish, primarily limpets, mussels, and turban shells. These sites are found in two distinct biogeographic regions, the west, Atlantic Ocean coast and the south, Indian Ocean coast, with different marine environments influencing the shellfish species available for human exploitation. We are currently excavating Ysterfontein 1, a Middle Stone Age shell midden on the west coast. Analyses of the mollusks from Ysterfontein I and other MSA and LSA assemblages illuminate ancient subsistence practices, environmental changes, and human population densities, and we particularly aim to address issues surrounding the emergence of fully modern humans. The abundance of shells in many sites demonstrates that mollusks were an important source of food for both MSA and LSA people. Throughout the MSA and LSA, the proportions of different shellfish species change through time, suggesting that changing sea levels or ocean conditions may have influenced the available species. However, in many respects MSA and LSA assemblages are different from each other. The MSA samples have a lower diversity of shellfish species, than LSA samples; they are poor in granular limpets; and they lack fish and rock lobster, which are common in many coastal LSA assemblages. In general, limpets and turban shells are larger in MSA assemblages than they are in LSA samples. We believe the sum suggests that MSA people foraged less intensively than LSA people, perhaps because they lived at lower population densities.
