The early evolution and palaeobiogeography of Mesozoic planktonic foraminifera
Malcolm B. Hart, Melissa J. Oxford, Wendy Hudson, 2002. "The early evolution and palaeobiogeography of Mesozoic planktonic foraminifera", Palaeobiogeography and Biodiversity Change: the Ordovician and Mesozoic–Cenozoic Radiations, J. A. Crame, A. W. Owen
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The planktonic foraminifera almost certainly evolved from benthonic ancestors in the early Jurassic. The meroplanktonic genus Conoglobigerina, known from south-central and eastern Europe, appears in the Bajocian and is probably derived from the even more geographically restricted Praegubkinella. This genus was represented by a single taxon in the earliest Toarcian but diversified after the Toarcian anoxic event. At the same level Oberhauserella quadrilobata Fuchs, 1967 became more inflated and there is some evidence to suggest that the ‘anoxic event’ was the environmental perturbation that began the transition to a planktonic mode of life. In the Callovian-Oxfordian interval, the planktonic foraminifera are still restricted to a relatively limited area bounded by the North Atlantic Ocean, NW Europe and Eastern Europe and this remained the case even in the earliest Cretaceous. It was only in the Aptian-Albian that the palaeogeographical distribution changed dramatically, probably as a response to the elevated sea levels caused by the increased rate of ocean crust production which began in the Early Aptian. The principal diversification events in the Jurassic (Toarcian, Bajocian, Callovian-Oxfordian) also appear to be related to sea level highstands.
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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.