Brachiopods: Cambrian-Tremadoc precursors to Ordovician radiation events
Michael G. Bassett, Leonid E. Popov, Lars E. Holmer, 2002. "Brachiopods: Cambrian-Tremadoc precursors to Ordovician radiation events", Palaeobiogeography and Biodiversity Change: the Ordovician and Mesozoic–Cenozoic Radiations, J. A. Crame, A. W. Owen
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Brachiopod-dominated palaeocommunities incorporating a structure typical of faunal groups within the Palaeozoic Evolutionary Fauna were already present in North and East Gondwana and associated terranes as early as the mid-Cambrian, confined exclusively to shallow marine, inshore environments. The late Cambrian and Tremadoc record of these faunas is incomplete, because of pronounced global sea-level lowstand and subsequent break-up and destruction of the Cambrian Gondwanan margin. It is likely, however, that those groups later forming the core of the Palaeozoic Evolutionary Fauna evolved originally in shallow-water environments of low-latitude peri-Gondwana, and dispersed widely when favourable ecological conditions developed. Conspicuous sea-level rise through the early to mid-Arenig provided newly available habitats in the expanding epeiric seas, where the new faunas evolved and diversified by the mid-Ordovician, when rapid drift separated the early Palaeozoic continents. Relatively short-lived precursor and transitional brachiopod assemblages can be identified on most of the main palaeocontinents prior to the Ordovician radiation of the Palaeozoic Evolutionary Fauna.
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The study of biodiversity through geological time provides important information for the understanding of diversity patterns at the present day. Hitherto, much effort has been paid to studying the mass extinctions of the Phanerozoic but the research emphasis has now changed to focus on what occurred between these spectacular catastrophic events. After the Cambrian ‘explosion’ of marine organisms with readily preservable skeletons, there have been two intervals when life radiated dramatically — the Ordovician Period, and the mid-Mesozoic-Cenozoic eras. These intervals saw a fundamental reorganization of biodiversity on a hierarchy of biogeographical scales. The size of these diversity increases and their probable causes are topics of intense debate, and there is an intriguing link between the dispersal of continents, changing climates and the proliferation of life.
The papers in this volume are written by palaeontologists, biogeographers and geologists addressing the highly topical field of palaeobiodiversity in the context of the Earth’s changing geography. Palaeobiogeography and Biodiversity Change: the Ordovician and Mesozoic-Cenozoic Radiations illustrates many aspects of the two great episodes of biotic radiation and shows how long periods of time and plate tectonic movements have a fundamental influence on the generation and maintenance of major extant biodiversity patterns.
The volume will be of interest to professional palaeontologists, biologists and geologists, as well as to students in earth and biological sciences.