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Palaeozoic |
Institute of Geology, Estonian Academy of Sciences, 7 Estonia Ave, EE0100 Tallinn, Estonia
The extinctions that occurred in the latest Ordovician and earliest and latest Wenlock, were the most impressive in the biotic history of this period. They were probably caused by glaciations. Recovery processes, more or less, follow the classical scenario: extinction-low-diversity survival interval-recovery through radiation events. Rather often there occurs diachrony of the phases of this scenario in the different groups discussed. Graptolite recovery was the most rapid with a diversity maximum in the mid-Llandovery. Their main extinction and low-diversity interval were in the latest Ordovician. The evolution of corals and acritarchs was slower — after a few lower-scale origination events a diversity burst was reached in the late Llandovery. An analogous but lower-scale pattern was noted at the very beginning and in the late Wenlock. The difference was caused by evolutionary and ecological reasons. A good correlation between diversity changes and terrestrial environmental events (glaciations, sea-level movements, stable isotope records) is noted.
