Paleontological Periods are divided into ERAS, which are the largest divisions of geological time. These ERAS are further divided into smaller units such as Periods and Epochs. The ERAS are the Cenozoic, Mesozoic, and Paleozoic. The Cenozoic Era is the most recent and includes the Holocene and Pleistocene Epochs. The Mesozoic Era is known as the Age of Reptiles and includes the Triassic, Jurassic, and Cretaceous Periods. The Paleozoic Era is the oldest and includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods.