Archaeocetes

Archaeoceti Temporal range: Eocene–Oligocene PreЄ Є O S D C P T J K Pg N
Cynthiacetus and Ambulocetus skeletons
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Infraorder:	Cetacea
Parvorder:	†Archaeoceti Flower 1883
Families and clades
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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 . 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.

All archaeocetes from the Ypresian (56–47.8 mya) and most from the Lutetian (47.8–41.3 mya) are known exclusively from Indo-Pakistan, but Bartonian (41.3–38.0 mya) and Priabonian (38.0–33.9 mya) genera are known from across Earth, including North America, Egypt, New Zealand, and Europe. Although there is no consensus regarding the mode of locomotion cetaceans were capable of during the late Lutetian, they were very unlikely to be nearly as well-adapted to the open ocean as living cetaceans. They probably reached as far as North America along coastal waters: either around Africa and over to South America, or, more likely, over the Tethys Sea (between Eurasia and Africa) and along the coasts of Europe, Greenland, and North America.

Some researchers are convinced, based on morphological similarities between archaeocetes (stem cetaceans) and neocetes, that the two living suborders of cetacean (the crown cetaceans) emerged from within Archaeoceti and therefore consider Archaeoceti paraphyletic or a non-natural group.Uhen 2008 introduced the clade Pelagiceti to accommodate the fully marine basilosaurids. Other researchers argue, despite these morphological similarities, that no archaeocete fossil have been placed within Neoceti, and therefore that the radiation of extant whales can be described independently of Archaeoceti.