The Great Ordovician Biodiversification Event (GOBE): Causes and Consequences of Diversity's Big Bang

摘要

The Ordovician Period (c. 488-444 Ma) witnessed the steepest rise in the biodiversity and biocom-plexity of marine life during the Phanerozoic, marked by the installation of a benthos dominated by suspension-feeding animals. These changes in the abundance of life associated with increased biotur-bation and tiering structures, set the agenda for subsequent marine ecosystems on the planet. Where-as the Cambrian Explosion generated a range of spectacular new body plans, it was not until some 20 Myr later that biodiversity at the family, genus and species level began to climb. Over an interval of some 25 Myr, accelerating γ (inter-provincial), β (inter-community), and a (intra-community) di-versities were initiated by high diversities amongst Early Ordovician benthic faunas, emerging from the widespread anoxia of the Furongian (late Cambrian), and associated with the dispersal of the continents and the high frequency of volcanic arcs and microcontinents (y diversity) against a back-ground of sustained sea level rise during warm climates. For example, the disparate and diverse as-semblages belonging to the Celtic, peri-Gondwanan and Toquima-Table Head, peri-Laurentian mar-ginal and oceanic provinces helped accelerate the event, providing geographic centres for speciation. Moreover, during the Early and Mid Ordovician, community types expanded particularly into deeper water and around carbonate platforms and within mound structures (β diversity) and more animals were squeezed into communities by the canalization of ecological niches permitting more diverse and densely packed associations (a diversity). Other factors such as an abundance of phyto and zoo-plankton and planktotrophic larvae, driving a plankton revolution together with periodic meteorite showers, fluctuations in the planet's climate and water temperature associated with sea-level changes may have provided critical resources and stimuli to a rapidly diversifying marine invertebrate fauna, participating in new trophic structures that reached its Palaeozoic plateau during the Late Ordovi-cian. Recent standardized curves for Phanerozoic diversity indicate that the peak of the Ordovician radiation was rarely exceeded during subsequent geological time, highlighting the GOBE as one of a handful of truly major biological events.