The Archaeoceti ('ancient whales'), or Zeuglodontes in older literature, is a group of primitive cetaceans. They lived from the early Eocene to the late Oligocene, 5523 million years ago (mya). They were the first cetacean radiation, and they include the first amphibious stages in cetacean evolution. So they are the ancestors of both modern cetacean suborders, Mysticeti and Odontoceti.