Eoceen

Eoceen, also spelled Eocene in English, is the name of the second epoch of the Paleogene Period in the Cenozoic Era. It spans roughly 56.0 to 33.9 million years ago. The term Eoceen is commonly used in Dutch and other languages; in English the standard form is Eocene.

Climate and environment: The early Eoceen was very warm, with tropical and subtropical forests extending into higher latitudes. The Paleocene–Eocene Thermal Maximum at the onset of the epoch stands as one of the most rapid global warm events in the Cenozoic. Through the middle of the epoch, global temperatures gradually cooled, and by the late Eocene extensive cooling led to widespread drying and the onset of Antarctic glaciation.

Biota: Mammals diversified and filled ecological roles left by earlier epochs. Early perissodactyls and artiodactyls appeared, and the first clearly modern horses emerged in the early Eocene. Primates evolved and diversified during the epoch. Ocean life included the first fully aquatic mammals and early whales of basilosaurid lineages.

Geography: Tectonic processes moved continents toward their present positions; the closing of the Tethys Sea and changes in ocean basins influenced climate patterns. India’s northward drift continued toward collision with Asia, setting the stage for the later uplift of the Himalayas.

End: The epoch ended with the Eocene–Oligocene transition around 33.9 million years ago, a period of significant global cooling and ice-sheet growth in Antarctica, which contributed to faunal turnover and the shift toward Oligocene assemblages.