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The Early Ordovician is the first epoch of the Ordovician period, corresponding to the Lower Ordovician series of the Ordovician system. It began after the Age 10 of the Furongian epoch of the Cambrian and lasted from 486.85 to 471.3 million years ago, until the Dapingian age of the Middle Ordovician.
The Ordovician Period in Britain was traditionally broken into Early (Tremadocian and Arenig), Middle (Llanvirn (subdivided into Abereiddian and Llandeilian) and Llandeilo) and Late (Caradoc and Ashgill) epochs. The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column.
The Ellesmerocerids were the only shelled cephalopods known to have survived the end-Cambrian extinction; all subsequent cephalopods are thus thought to be derived from these forms, which diversified throughout the Ordovician period. Early cephalopods had fine shells that could not cope with the pressures of deep water. [2]
The Ordovician mass extinction did not leave the trilobites unscathed; some distinctive and previously successful forms such as the Telephinidae and Agnostida became extinct. The Ordovician marks the last great diversification period amongst the trilobites: very few entirely new patterns of organisation arose post-Ordovician.
The Hirnantian glaciation, also known as the Andean-Saharan glaciation, Early Paleozoic Ice Age (EPIA), [1] the Early Paleozoic Icehouse, [2] the Late Ordovician glaciation, or the end-Ordovician glaciation, occurred during the Paleozoic from approximately 460 Ma to around 420 Ma, during the Late Ordovician and the Silurian period.
The Cambrian–Ordovician extinction event, also known as the Cambrian-Ordovician boundary event, [1] was an extinction event that occurred approximately 485 million years ago in the Paleozoic era of the early Phanerozoic eon. [2]
The Great Ordovician Biodiversification Event (GOBE) was an evolutionary radiation of animal life throughout [1] the Ordovician period, 40 million years after the Cambrian explosion, [2] whereby the distinctive Cambrian fauna fizzled out to be replaced with a Paleozoic fauna rich in suspension feeder and pelagic animals.
Taconic phase – Mountain-building period that affected most of New England – In the northeastern U.S. and Canada, during the Ordovician Period; Acadian phase – North American orogeny – In the eastern U.S., during the Silurian and Devonian Periods