Paleocene

Paleocene is the first epoch of the Paleogene Period in the Cenozoic Era, spanning roughly 66 to 56 million years ago. The name means “old recent,” marking its position after the Cretaceous and before the Eocene. The epoch begins at the Cretaceous–Paleogene boundary, which coincides with a mass extinction that ended most non-avian dinosaurs and cleared ecological space for mammals, birds, and other groups to diversify.

During much of the Paleocene the global climate was warm and largely ice-free, with high sea levels and forests extending into higher latitudes. A long-term cooling trend began late in the epoch, while continental configurations continued to shift and the Atlantic Ocean widened. These changes influenced ocean and atmospheric circulation and biodiversity patterns.

Biota and ecosystems recovered and diversified after the K–Pg extinction. Mammals and birds expanded into new niches, including early herbivores and carnivores, and several placental mammal lineages began to emerge. Primitive primate-like mammals appear in the record, along with other groups that would later give rise to modern orders. Flora recovered with robust angiosperm forests, and plant communities continued to adapt to a warming-cooling cycle.

Subdivisions and end: The Paleocene is divided into three ages—Danian, Selandian, and Thanetian—marking early, middle, and late Paleocene time. The epoch ends with the Paleocene–Eocene Thermal Maximum, around 56 million years ago, a rapid global warming event that ushered in the Eocene and significant biotic and climatic changes.