New insights from exceptionally preserved Ordovician biotas from Morocco

The Great Ordovician Biodiversification Event was a pivotal episode in the history of life, replacing the Cambrian Evolutionary Fauna by the Palaeozoic Evolutionary Fauna which dominated the marine realm until the end-Permian mass extinction. During this Ordovician radiation, most phyla diversified more rapidly than at any other time in the Phanerozoic: diversity increased twofold at the ordinal level, three times at the family level, and nearly four times at the genus level (Droser and Finnegan, 2003; Harper, 2006; Webby et al., 2004). Our knowledge of Ordovician communities is based almost entirely on the mineralised fossil record; although exceptionally preserved biotas have an important role to play in unravelling the evolution of Ordovician organisms and ecosystems, their contribution so far has been limited because of their scarcity and the fact that the few known Middle and Late Ordovician assemblages represent restricted marine environments (Farrell et al., 2009; Liu et al., 2006; Young et al., 2007). This situation recently improved markedly with the discovery of two exceptionally preserved biotas in the Ordovician of south-eastern Morocco