The Great Ordovician Biodiversification Event (GOBE): The palaeoecological dimension
Abstract The ‘Great Ordovician Biodiversification Event’ (GOBE) saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so-called ‘Cambrian Explosion’. The diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them. The present paper reviews the palaeoecological dimension of the GOBE. It involved major increases in α, s and γ biodiversity largely associated with the rise of the Paleozoic Evolutionary Fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the Ecological Evolutionary Units P1 and P2. In the benthos, these include more complex food webs than those of the Cambrian, greater tiering, especially above the sediment–water interface, and the development of guild structures indicating increased competition between taxa for particular resources. The Ordovician is characterized by a profound change in reef composition, with a switch from microbial-dominated reefs in the Early and Middle Ordovician to metazoan-dominated reefs in the Late Ordovician. Increases in complexity of deep-water trace fossil assemblages began in the Early Ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities. Within the water column, the GOBE involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton (including planktotrophic larvae from a range of invertebrate clades). This revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates, molluscs and arthropods and promoted the rise of suspension feeders in the benthos. An escalation amongst predators and thus community evolution may also have been a major driver of biodiversification.