Paleocene Epoch, the lowest (oldest) division of the Tertiary Period of geologic time. The epoch began about 65,000,000 years ago and lasted 11,000,000 years. Its name is from the Greek for ancient recent, and refers to the epoch's plant and animal life, which was beginning to resemble that of the present day. Flowering plants spread rapidly over the world in the warm, moist climate of the Paleocene. Mammals became the dominant form of life. Most of the modern orders of mammals were in existence during this epoch, but the present-day species had not yet evolved.
During Paleocene time the southern Atlantic and Gulf states of the United States were covered by the sea. In this region, Paleocene rocks contain bauxite and petroleum. The Rocky Mountains, uplifted just before the epoch began, were much eroded in some areas of the West to form thick sediments (called the Fort Union series).