Great Ordovician Biodiversification Event

Great Ordovician Biodiversification Event
Name	Great Ordovician Biodiversification Event
Period	Ordovician
Epoch	Early to Middle Ordovician
Duration	~40 million years
Significance	Major Phanerozoic marine biodiversification

Great Ordovician Biodiversification Event The Great Ordovician Biodiversification Event was a major increase in marine biodiversity during the Ordovician Period, involving a rise in taxonomic richness and ecological complexity across global shallow seas. It transformed Paleozoic faunas and set the stage for subsequent developments in marine ecosystems, leaving a record preserved in strata on multiple continents and studied by paleontologists and geologists worldwide.

Background and timing

The event unfolded primarily in the Ordovician between the Tremadocian and the Sandbian stages, peaking in the Middle Ordovician and intersecting with chronostratigraphic units defined by the International Commission on Stratigraphy and regional schemes such as the Baltica and Laurentia frameworks. Correlative evidence comes from radiometric constraints tied to the Geological Time Scale and biostratigraphic markers like graptolites and conodonts used by researchers at institutions including the British Geological Survey and the United States Geological Survey. Work by paleontologists affiliated with universities such as Yale University, University of Cambridge, and University of Edinburgh refined the temporal resolution, linking diversification pulses to stage boundaries recognized by the International Union of Geological Sciences.

Causes and environmental drivers

Hypotheses for drivers implicate interactions among tectonics, climate, and ocean chemistry involving plates like Gondwana, Laurentia, and Siberia, with contributions from orogenies recorded in the Taconic Orogeny and the Caledonian orogeny. Changes in atmospheric and oceanic chemistry, including fluctuations in carbon dioxide reconstructed from proxies used by researchers at Lamont–Doherty Earth Observatory and Scripps Institution of Oceanography, coincide with global cooling episodes inferred from oxygen isotope work by teams at ETH Zurich and the University of California, Santa Cruz. Increased nutrient flux from weathering tied to uplift and erosion, modeled in studies involving the Paleoclimate Modeling Intercomparison Project, likely enhanced primary productivity in epicontinental seas, with evidence from shale successions studied by the Natural History Museum, London and the Smithsonian Institution. Sea-level changes documented in sequence stratigraphy by investigators at Indiana University and Utrecht University created widespread continental shelves that fostered habitat expansion.

Patterns of diversification and ecological expansion

Diversification manifested as increases in genus- and family-level richness recorded in databases compiled by researchers associated with the Paleobiology Database and analytical platforms used by the National Center for Ecological Analysis and Synthesis. Ecological expansion included development of complex trophic webs observed in Lagerstätten such as the Boden Group and faunas from the Burgess Shale-analogous settings, though temporally distinct. Studies published in journals like Nature and Paleobiology indicate tiering of benthic communities, proliferation of suspension-feeding strategies, and escalating bioturbation documented by sedimentologists at University of Copenhagen and University of Toronto. Quantitative work by teams from Princeton University and Stanford University applied diversity partitioning and origination-extinction models showing pulses of radiation and ecological incumbency patterns associated with regional faunal turnovers tracked across museum collections including the Natural History Museum of Los Angeles County.

Major taxonomic groups affected

Brachiopods, trilobites, and bryozoans underwent substantial radiations, with taxonomic revisions contributed by scholars at American Museum of Natural History and Royal Ontario Museum. Molluscan groups such as gastropods and bivalves expanded in diversity, discussed in monographs from Smithsonian Institution Press and research by paleontologists at University of Chicago. Cephalopods diversified in predatory roles, with phylogenetic work from Harvard University and University of Tokyo. Echinoderms, including early crinoids and cystoids, show morphological innovation studied by teams at Field Museum and University of Michigan. Planktonic organisms—graptolites and radiolarians—exhibit evolutionary trends used in biostratigraphy by researchers at University of Oxford and Geological Survey of Canada. Microbial mats and stromatolites recorded in formations investigated by University of Western Australia indicate microbial contributions to ecosystem engineering.

Biogeography and provinciality

Biogeographic patterns reflect increasing provinciality and endemism across paleocontinents including Avalonia, Perunica, and Kazakhstania, reconstructed through faunal lists curated by the Paleobiology Database and regional syntheses produced by the Geological Society of America. Plate reconstructions developed by researchers at Pennsylvania State University and Caltech elucidate dispersal corridors and barriers shaped by ocean currents modeled in work at National Oceanic and Atmospheric Administration. Provincial differences in trilobite and brachiopod assemblages are documented in fieldwork reports from sites in Wales, Argentina, and China and museum collections at institutions like the Natural History Museum, Stockholm.

Extinction events and long-term legacy

Although not itself a mass extinction, the biodiversification was punctuated by regional extinctions and culminated in the Late Ordovician mass extinction linked to glaciation on Gondwana and oceanographic upheaval investigated by teams at McGill University and University of Texas at Austin. The long-term legacy includes establishment of Phanerozoic-style marine ecosystems that influenced later radiations recorded in the Silurian and beyond, informing evolutionary theory developed at centers such as University of California, Berkeley and influencing collections and exhibits at the Natural History Museum, London and Smithsonian Institution.

Category:Ordovician