Early Diversification of Ordovician Graptolites in Jiangnan Slope, South China

摘要

INTRODUCTION By using a factor-analytic method in 1981, Sepkoski recognized three great evolutionary faunas in the Phanerozoic diversity history of marine animal families. Each evolutionary fauna appears to be associated with a distinct phase of diversification. The Paleozoic fauna, present between the Cambrian and the 'modern' faunas, is associated with the Ordovician radiation and the long Paleozoic equilibrium (Sepkoski, 1984, 1981). The most intensive part of the Ordovician radiation was during the Middle to Late Ordovician, but some other taxonomic groups (e.g., trilobites, inarticulate brachiopods, graptolites, conodonts and rostroconch mollusks) also diversified significantly during the Early Ordovician. Therefore, all these diversification events from the beginning to the end of the Ordovician should be treated as belonging to the Ordovician radiation (Webby, 2004).