Palaeobiogeography of Ordovician echinoderms
Bertrand Lefebvre, Colin D. Sumrall, Rene A. Shroat-Lewis, Mike Reich, Gary D. Webster, Aaron W. Hunter, Elise Nardin, Sergei V. Rozhnov, Thomas E. Guensburg, Alexandra Touzeau, Fleur Noailles, James Sprinkle, 2013. "Palaeobiogeography of Ordovician echinoderms", Early Palaeozoic Biogeography and Palaeogeography, D. A. T. Harper, T. Servais
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The palaeobiogeographical distribution of the six major clades of Ordovician echinoderms (asterozoans, blastozoans, crinoids, echinozoans, edrioasteroids and stylophorans) is analysed based on a comprehensive and up-to-date database compiling 3701 occurrences (1938 species recorded from 331 localities) of both complete specimens and isolated ossicles. Although historically biased towards a limited number of regions (Europe, North America, Russia), the resulting dataset makes it possible to identify six main palaeobiogeographical provinces for Ordovician echinoderms: Laurentia, Baltica, West Gondwana, East Gondwana, Avalonia and Siberia. At a global scale, the high endemicity of echinoderms during the Early to Middle Ordovician coincides with the time of maximum dispersal of continental masses. Late Ordovician faunas tend to become more cosmopolitan, possibly as a consequence of changing palaeogeography and/or relatively higher sea-levels in the Sandbian–Katian interval. Regional biodiversity patterns of Ordovician echinoderms confirm that their major diversification during the Ordovician is not a single, universal evolutionary event, but rather results from the complex addition of contrasted local evolutionary trends.
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The Early Palaeozoic was a critical interval in the evolution of marine life on our planet. Through a window of some 120 million years, the Cambrian Explosion, Great Ordovician Biodiversification Event, End Ordovician Extinction and the subsequent Silurian Recovery established a steep trajectory of increasing marine biodiversity that started in the Late Proterozoic and continued into the Devonian. Biogeography is a key property of virtually all organisms; their distributional ranges, mapped out on a mosaic of changing palaeogeography, have played important roles in modulating the diversity and evolution of marine life. This Memoir first introduces the content, some of the concepts involved in describing and interpreting palaeobiogeography, and the changing Early Palaeozoic geography is illustrated through a series of time slices. The subsequent 26 chapters, compiled by some 130 authors from over 20 countries, describe and analyse distributional and in many cases diversity data for all the major biotic groups plotted on current palaeogeographic maps. Nearly a quarter of a century after the publication of the ‘Green Book’ (Geological Society, London, Memoir 12, edited by McKerrow and Scotese), improved stratigraphic and taxonomic data together with more accurate, digitized palaeogeographic maps, have confirmed the central role of palaeobiogeography in understanding the evolution of Early Palaeozoic ecosystems and their biotas.