The Great Ordovician Biodiversification Event (gobe): Looking Under the Curve

Initial studies by Sepkoski in 1975 and Webby et al. in 2004 established, respectively, ‘the Ordovician radiations’ and the ‘Great Ordovician Biodiversification Event’ (GOBE) as a key macroevolutionary event in the history of marine life. Nevertheless to date, with exception of the pioneer paper of Droser and Sheehan in 2007 and a few more recent studies (e.g. Servais et al. in 2010, 2021; Harper et al. in 2020), the majority of investigations of the GOBE have been focussed on numerical data from taxonomic counts neglecting the ecological processes under the biodiversity curves. Peaks in Ordovician taxonomic biodiversity have been related to fluctuations in ambient settings including climatic conditions, nutrient delivery, oxygen levels together with continental fragmentation and movements and the generation of island arcs. Here, using corrected data from the Paleobiology Database, partitioned into benthos, nekton and plankton together with reef-building organisms, we indicate the major sustained diversifications of these ecological groups during extended Ordovician radiations. Ecological activity under the curve was intense with the post-Cambrian escalation of a range of new life styles within the benthos occupying new habitats involving a marked increase in suspension-feeding epifauna and a range of deposit feeders. Marked too was the increase in pelagic carnivorous predators within the vertebrates (chrondrichtheyans and placoderms), the chordates (condontophorids) and molluscs (cephalopods). The benthos, nekton and plankton interacted to establish a more modern marine ecosystem.