The Ordovician radiation was the diversification of animal life at the start of the Ordovician period, just 40 million years after the Cambrian explosion.[1] It followed a series of extinction events at the Cambrian-Ordovician boundary, and the resulting fauna went on to dominate the Palaeozoic relatively unchanged.[2]. Marine diversity to levels typical of the Palaeozoic,[3] and disparity was similar to today's.[4][5] The diversity increase was neither global nor instantaneous; it happened at different times in different places.[2]
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Causes
The causes of the explosion are complex, and probably varied for different localities. Possible causes include changes in palaeogeography or tectonic activity, as well as a modified nutrient supply.[6]
The above triggers would have been amplified by ecological escalation, whereby any new species would co-evolve with others, creating new niches through niche partitioning, tropic layering, or by providing a new habitat.[clarification needed][6]
Effects
The only phylum not to be represented in the Cambrian period, the Bryozoa, is first observed after this Ordovician radiation. Diversity increased manifold; the total number of marine orders doubled, and families tripled.[2]
The acritarch record displays the Ordovician radiation beautifully; both diversity and disparity peaked in the middle Ordovician.[1] The warm waters and high sea level (this had been rising steadily since the early Cambrian) permitted large numbers of phytoplankton to prosper; the accompanying diversification of the phytoplankton may have caused an accompanying radiation of zooplankton and suspension feeders.[1]
The planktonic realm was invaded as never before, with several invertebrate lineages colonising the open waters and initiating new food chains at the end of the Cambrian into the early Ordovician.[7]
See also
References
- ^ a b c Servais, T.; Lehnert, O.; Li, Jun; Mullins, G.L (2008). "The Ordovician Biodiversification: Revolution in the Oceanic Trophic Chain". Lethaia 41: 99. doi:.
- ^ a b c Droser, Mary L.; Finnegan, Seth (2003). "The Ordovician Radiation: A Follow-up to the Cambrian Explosion?". Integrative and Comparative Biology 43 (1): 178. doi:.
- ^ Marshall, C. (2006). "Explaining the Cambrian "Explosion" of Animals". Annual Review of Earth and Planetary Sciences 34: 355–384. doi:. http://arjournals.annualreviews.org/doi/full/10.1146/annurev.earth.33.031504.103001.
- ^ Bush, A.M.; Bambach, R.K.; Daley, G.M (2007). "Changes in Theoretical Ecospace Utilization in Marine Fossil Assemblages Between the Mid-Paleozoic and Late Cenozoic". Paleobiology 33 (1): 76–97. doi:. http://www.bioone.org/perlserv/?request=get-abstract.
- ^ Bambach, R.K.; Bush, A.M.; Erwin, D.H (2007). "Autecology and the Filling of Ecospace: Key Metazoan Radiations". Palaeontology 50: 1. doi:.
- ^ a b Botting, Muir (2008). "Unravelling Causal Components of the Ordovician Radiation: the Builth Inlier (Central Wales) As a Case Study". Lethaia 41: 111. doi:.
- ^ Full text at PMC: 2749442
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