Eocene–Oligocene extinction event

The Eocene–Oligocene extinction event, also called the Eocene-Oligocene transition (EOT), is the transition between the end of the Eocene and the beginning of the Oligocene, an extinction event and faunal turnover occurred from around 33.9 to 33.4 million years ago. It was marked by large-scale extinction and floral and faunal turnover, although it was relatively minor in comparison to the largest mass extinctions.

Source: Wikipedia — Eocene–Oligocene extinction event (CC BY-SA 4.0)