Cetacea

The lineage of whales, dolphins and porpoises. Its Eocene fossils document a sequence from terrestrial or amphibious relatives to fully aquatic forms; living members comprise Odontoceti and Mysticeti.

A soft-tissue propulsive structure of the tail. It should not be drawn as a directly preserved fossil feature when only skeletal evidence is available.

A member of a late Eocene whale radiation with a fully aquatic body plan and strongly reduced hind limbs.

A late Eocene whale retaining small hind limbs incapable of supporting terrestrial walking. ^[ref]

A member of an Eocene grade of whales documenting increasing aquatic specialization. Named fossil grades need not be monophyletic under every analysis.

An Eocene whale whose ankle anatomy supplies evidence of artiodactyl relationships. A reconstructed tail fluke is not a directly preserved observation in its known skeletons. ^[ref]

An Eocene whale with a combination of robust limbs and aquatic locomotor specializations.

An early whale of the family Pakicetidae, with diagnostic ear anatomy but a largely terrestrial skeleton. ^[ref]

The whale lineage containing living baleen-bearing species and their extinct relatives, including toothed forms. Adult toothlessness is a derived feature of the living radiation.

Keratinous plates used in filtering food in living mysticetes. Its presence in a fossil may be inferred from associated anatomy but must not be confused with direct preservation of the plates. ^[ref]

The living toothed-whale lineage, including dolphins and porpoises. Specialized sound production and echolocation are important components of its sensory biology.