Editorial Preface to Special Issue: The radiations within the Great Ordovician Biodiversification Event

In order to improve our understanding of the biodiversification of marine life that took place during the early Palaeozoic, we present this special issue focused on the Ordovician radiations. The Great Ordovician Biodiversification Event (GOBE) is a conceptual term that is today largely used to refer to the most significant increase of marine biodiversity of the Phanerozoic that occurred during the Ordovician Period between 485 and 444 Ma. Some authors, focusing on taxonomic diversity counts of selected groups, understand the GOBE to be related to a single dramatic biodiversification event of short duration in the Darriwilian Stage of the Middle Ordovician Series between 470 and 455 Ma, whereas others follow the more traditional view and consider the Ordovician biodiversification as an aggregation of radiation events capturing a large and complex increase of taxonomic diversity but also ecological complexity of marine organisms covering the entire Ordovician. This special issue features 16 selected papers that provide different perspectives on these Ordovician biodiversification events, illustrating a variety of radiations occurring during the Ordovician Period. Several papers focus on the available biodiversity datasets and their biases, and the difficulty to distinguish and interpret the various regional and global scales. It becomes clear that the Cambrian and Ordovician radiations are artificially separated by a late Cambrian 'Furongian Biodiversity Gap' and that a single long-term early Palaeozoic radiation is more and more visible. A few papers provide additional data on this crucial interval across the CambrianOrdovician boundary displaying a much higher ecological complexity than previously assumed. Both the diversification of the plankton and the evolution of nektonic groups during the Ordovician are investigated, in papers including Computational Fluid Dynamic simulations. The virtual special issue closes with papers documenting the development of reefs during the Late Ordovician.