In geologic time, the Tertiary Period (also sometimes referred to in terms of a Paleogene Period and a Neogene Period), represents the first geologic period in the Cenozoic Era. The Tertiary Period spans the time between roughly 65 million years ago (mya) and 2.6 mya. When referred to in terms of a Paleogene Period and a Neogene Period, the Paleogene Period extends from approximately 65 mya to 23 mya, and the Neogene Period from 23 mya to 2.6 mya.

The Tertiary Period contains five geologic epochs. The earliest epoch, the Paleocene Epoch, ranges from approximately 65 mya to 55 mya. The Paleocene Epoch is further subdivided into (from earliest to most recent) Danian and Thanetian stages. The second epoch, the Eocene Epoch ranges from approximately 55 mya to 34 mya. The Eocene Epoch is further subdivided into (from earliest to most recent) Ypresian, Lutetian, Bartonian, and Priabonian stages. The third epoch of the Tertiary Period, the...