Paleogene

The Paleogene is a period in the geologic timescale that marks the first part of the Cenozoic Era, following the mass extinction at the end of the Cretaceous. It spans from about 66 million years ago to 23.03 million years ago, ending with the start of the Neogene. The period is divided into three epochs: Paleocene (66–56 Ma), Eocene (56–34 Ma), and Oligocene (34–23 Ma).

During the Paleogene, life recovered from the Cretaceous–Paleogene extinction and mammals and birds diversified rapidly. Early in the Paleocene, mammals became more abundant and varied in size and form. By the Eocene, many modern mammal orders were present, and primates and other groups trace their origins to this interval. Marine mammals also emerged and diversified during the period. Plants diversified as well, with angiosperms continuing to expand their ecological dominance. The climate began warm in the early Paleogene, with the Eocene featuring one of the warmest periods in Earth’s history. A transition toward cooler, more variable conditions began in the late Eocene and culminated in significant global cooling at the Eocene–Oligocene boundary, contributing to Antarctic glaciation and the spread of cooler, dryer environments.

Geologically, the Paleogene was marked by active plate tectonics that reshaped continents and oceans. The opening of the North Atlantic continued, and mountain-building events linked to the uplift of the Himalayas and other ranges began to influence climate and biodiversity. The Paleogene thus set the stage for the evolutionary and ecological developments that characterized the Neogene and the rest of the Cenozoic.