Archaeoceti

Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (55 to 23 million years ago). Representing the earliest cetacean radiation, they include the initial amphibious stages in cetacean evolution and are thus the ancestors of both modern cetacean suborders, Mysticeti and Odontoceti. This initial diversification occurred in the shallow waters that separated India and Asia 53 to 45 mya, resulting in some 30 species adapted to a fully oceanic life; though both echolocation and filter-feeding evolved during a second radiation 36 to 35 mya.