Palaeogene: early Cenozoic period of mammal diversification and climate change

Subdivisions and timeline

The Palaeogene comprises three standard epochs: the Paleocene, the Eocene and the Oligocene. These epochs are commonly recognized in global chronostratigraphy and are further divided into ages used by geologists and paleontologists. Key boundaries are tied to changes in fossil assemblages, isotopic excursions and abrupt shifts in climate.

Climate, environments and life

The Palaeogene saw dramatic climatic shifts. The early Paleocene remained relatively warm following the end-Cretaceous extinction. The middle of the period experienced one of the best-known transient warming events, the Paleocene–Eocene Thermal Maximum, which led to rapid global temperature rise and profound effects on marine and terrestrial life. Later, through the Oligocene, global temperatures cooled and the Antarctic ice sheet began to form, altering ocean circulation and habitats.

Biological and ecological significance

With non-avian dinosaurs gone, mammals underwent a major adaptive radiation: many modern groups — such as primates, rodents, ungulates and carnivores — first appear or diversify significantly in Palaeogene deposits. Birds and flowering plants also expanded into new niches. Marine ecosystems saw turnover among plankton, foraminifera and early modern groups of fish and marine mammals.

Geology, plate movements and resources

Tectonic reorganization continued during the Palaeogene as continents moved toward their present positions; orogenic activity (mountain building) accelerated in some regions and ocean gateways changed, influencing climate. Sedimentary rocks of Palaeogene age are important reservoirs for fossil fuels and host many fossil sites that preserve the transition to modern ecosystems.

Terminology and historical usage

Historically the Palaeogene together with the following Neogene were grouped under the older name Tertiary, a term still used informally. Modern stratigraphic practice treats the Palaeogene as a distinct period to reflect its unique biological and climatic developments. For further introductory information see general period guides, regional stratigraphic charts (Cainozoic overviews), epoch summaries (Paleocene, Eocene, Oligocene) and sources on the end-Cretaceous extinction and early Cenozoic evolution (Cainozoic, Phanerozoic, eon). Additional background is available in palaeoclimate and stratigraphy summaries (66 Ma studies).

• Key epochs: Paleocene, Eocene, Oligocene.
• Follows the Cretaceous; precedes the Neogene.
• Often contrasted with the historical term Tertiary.