Cambrian–Ordovician extinction event

The Cambrian–Ordovician extinction event occurred approximately 488 million years ago (m.y.a.). This early Phanerozoic Eon extinction event eliminated many brachiopods and conodonts, and severely reduced the number of trilobite species.

It was preceded by the less-documented (but probably worse) End-Botomian extinction event around 517 million years ago and the Dresbachian extinction event about 502 million years ago.

The Cambrian–Ordovician event ended the Cambrian Period, and led into the Ordovician Period in the Paleozoic Era.