Late Devonian mass extinction

The Late Devonian mass extinction, also known as the Kellwasser event, was a mass extinction event which occurred around 372.15 million years ago, at the boundary between the Frasnian and Famennian ages of the Late Devonian period. It is placed as one of the "Big Five" most severe mass extinction events in Earth's history, with likely around 40% of marine species going extinct, though the degree of severity is contested.

Source: Wikipedia — Late Devonian mass extinction (CC BY-SA 4.0)