Cambrian–Ordovician extinction event

Marine extinction intensity during Phanerozoic
%
Millions of years ago
The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised Capitanian mass extinction event are clickable links; see Extinction event for more details. (source and image info)

The Cambrian–Ordovician extinction event, also known as the Cambrian-Ordovician boundary event, was an extinction event that occurred approximately 485 million years ago (mya) in the Paleozoic era of the early Phanerozoic eon. It was preceded by the less-documented (but probably more extensive) End-Botomian mass extinction around 517 million years ago, and the Dresbachian extinction event about 502 million years ago.

The Cambrian–Ordovician extinction event ended the Cambrian period, and led into the subsequent Ordovician period. It eliminated many brachiopods and conodonts, and severely reduced the number of trilobite species.

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