Phylogeny of the Reedocalymeninae (Trilobita): implications for Early Ordovician biogeography of Gondwana
Samuel T. Turvey, 2002. "Phylogeny of the Reedocalymeninae (Trilobita): implications for Early Ordovician biogeography of Gondwana", Palaeobiogeography and Biodiversity Change: the Ordovician and Mesozoic–Cenozoic Radiations, J. A. Crame, A. W. Owen
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The shallow-water Neseuretus Association has been recognized by many authors as an important indicator of the former extent of Gondwana during the Early Ordovician. Phylogenetic relationships of the Reedocalymeninae (Arenig-?Early Silurian) were investigated using cladistic analysis, incorporating 22 species of Neseuretus as well as representatives of all other reedocalymenine genera. The area cladogram derived from this analysis contains four subclades each containing areas that span much of the palaeogeographic extent of Gondwana, which are interpreted as representing separate biogeographic events during the evolution of the subfamily. As the majority of taxa included in the analysis are associated with shallow shelf facies, this suggests that no significant environmental barriers existed across the continent during the Early Ordovician. Consideration of area relationships both for different subclades within the area cladogram, and within a consensus area cladogram, also supports the idea of a faunal cline between eastern and western Gondwana during this time interval. Further cladistic analysis of different trilobite taxa can be used to test these ideas.
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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.