Ypresian

Ypresian is the earliest age or stage of the Eocene Epoch in the International Commission on Stratigraphy (ICS) timescale. It is named after Ypres (Ieper), a city in Belgium, where rocks of this age were first studied. The interval spans about 56.0 to 47.8 million years ago and is followed by the Lutetian; it succeeds the Thanetian, the last stage of the Paleocene.

The lower boundary marks the Paleocene–Eocene boundary and is associated with the Paleocene–Eocene Thermal Maximum, a major global warming event. The Ypresian climate was globally warm with high sea levels; forests extended into higher latitudes and tropical conditions persisted in many regions.

The period records significant mammalian diversification, including early members of several modern groups such as primates and perissodactyls, as well as early cetaceans and other marine mammals. Marine faunas expanded in warm, shallow seas, and plant life included extensive tropical and subtropical assemblages. The Ypresian is represented in sedimentary sequences around the world, including marine basins and continental basins.

In stratigraphy, the Ypresian is sometimes subdivided into lower and upper portions in various regional schemes. See also Eocene, Paleogene, Lutetian, Thanetian.