BIOGEOGRAPHIC EVENTS IN THE MIDDLE AND UPPER CAMBRIAN, USING THE EXAMPLE OF THE AGNOSTIDA (TRILOBITA) AND BRACHIOPODA

Abstract

The dynamics of faunal diversity of planktonic agnostid trilobites and benthic brachiopods in different paleobasins is compared. The diversity dynamics in these two groups was similar in paleobasins characterized by unfavorable natural conditions and under the effect of strong extrinsic factors. In warm basins, the diversity dynamics in the two groups had little in common and was controlled by their evolutionary development. Regional cladograms of agnostid and brachiopod faunas for each zone of the Middle Cambrian and the beginning of the Upper Cambrian are proposed. The biogeographic schemes for both agnostids and brachiopods are basically specific; however, the Australian fauna acquired certain similarity to Siberian and Kazakhstan faunas and simultaneously diverged from the fauna of western North America. These processes were caused by extrinsic events.