Biogeographical patterns of Ordovician ostracods
Tõnu Meidla, Oive Tinn, Maria José Salas, Mark Williams, David Siveter, Thijs R. A. Vandenbroucke, Koen Sabbe, 2013. "Biogeographical patterns of Ordovician ostracods", Early Palaeozoic Biogeography and Palaeogeography, D. A. T. Harper, T. Servais
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The biogeography of marine shelf ostracod genera is analysed for two Ordovician time slabs, the earliest Late Ordovician and the terminal Ordovician, that have been considered to reflect comparatively warmer and cooler global climate states, respectively. The earlier time slab is equivalent to the Nemagraptus gracilis graptolite interval (centred about 460 Ma), and defined as the total range of the eponymous species. The Hirnantian time slab comprises the Normalograptus extraordinarius and Normalograptus persculptus graptolite biozones (445.6–443.7 Ma). The ostracod dataset consists of 160 taxa from 24 early Late Ordovician localities and 86 taxa from 10 Hirnantian localities. Ordination and variation partitioning analyses show that patterns in ostracod distribution in the gracilis time slab are largely related to palaeocontinental affinity of the samples and to a lesser degree to palaeolatitude. Some decrease of provincialism can be suggested for the Hirnantian, although the ostracod dataset is limited for this interval.
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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.