Bed-by-bed sampling of brachiopods from selected Kundan Stage localities in the East Baltic has permitted the construction of a-diversity curves, unprecedented in detail from this particular stage and region. These a-diversity curves can be correlated between the investigated sections, along an east to west transect of some 200 km and indicate bioevents associated with intervals of increased palaeo-water depth. The highest peaks in a-diversity occur when biofacies analysis and sedimentological evidence indicate drowning events. The events involve mainly taxa endemic to the Baltic province at this time and thus, the radiation proceeded by a modest expansion of the brachiopod fauna into deeper-water environments, isolated at this time from major immigrations. In addition to increased a-diversity, ß-diversity was signalled by new, deeper-water communities and the isolation of the province helped retain high values of ¿-diversity.