The Great Ordovician Biodiversification Event (GOBE): definition, concept and duration

The Ordovician biodiversification has been recognized since the 1960s; the term ‘The Great Ordovician Biodiversification Event’, abbreviated by many as the ‘GOBE’, has been used for the past 20 years. The conceptual development and terminology applied to this crucial episode in marine life signify its considerable complexity. The GOBE includes successive biodiversity phases of the pelagic and benthic biotas, possibly decoupled. Put simply, the GOBE can be seen as a sequence of diversifications of the planktonic (late Cambrian–Early Ordovician), level-bottom benthic (Early–Middle Ordovician) and reef communities (Middle–Late Ordovician), although the boundaries of these ‘events’ are diachronous (as for the entire GOBE), and it is logical to assume that these communities co-evolved and interacted. The GOBE also includes several Biotic Immigration Events (BIMEs), such as the ‘Richmondian Invasion’ and the ‘Boda Event’, recording the large-scale dispersal of taxa from one biogeographical area to another. The GOBE is thus the sum of the diversity trends of all individual fossil groups showing rapid increases, diachronously, during different intervals and across different regions. It thus spans the entire Ordovician, capturing the increasing total diversity of marine organisms during the period. The GOBE is not simply one, but many sequential events