Eocene cetaceans

Perucetus is an extinct genus of an early whale from Peru that lived during the Bartonian age of the middle Eocene. Perucetus is the largest Eocene whale, with length estimates varying from to . It was initially claimed to have rivaled or exceeded the modern blue whale in weight, partly due to the incredibly thick and dense bones this animal possessed, coupled with its already great size, but subsequent studies argued that it was significantly lighter. The ecology of Perucetus also remains largely mysterious. Based on the fossils, it was likely a slow-moving inhabitant of shallow waters. Its d

Mystacodon is a genus of toothed baleen whale from the Late Eocene Yumaque Member of Paracas Formation (previously called as Yumaque Formation) of the Pisco Basin in southwestern Peru. It is the oldest known baleen whale, and was probably a suction feeder of small prey on the seafloor.

Tutcetus is an extinct genus of diminutive basilosaurid cetacean from the Bartonian of Egypt. Tutcetus, named after the child pharaoh Tutankhamun, is both one of the oldest known basilosaurids from Africa and the smallest member of the family. It is suggested that the type specimen, a subadult close to maturity, only measured approximately long. The genus is monotypic, only including the species T. rayanensis.

Llanocetidae is an extinct family of ancient toothed baleen whales from the Eocene. It was named by American paleontologist Edward Mitchell in 1989 after describing the Antarctic Llanocetus, but a 2018 study by paleontologists Ewan Fordyce and Felix Marx included the Peruvian Mystacodon and an undescribed New Zealand specimen OU GS10897.

Llanocetus ( "Llano's whale" ) is a genus of extinct toothed baleen whales from the Late Eocene of Antarctica and New Zealand. The type species, Llanocetus denticrenatus, reached gigantic proportions, with the juvenile specimen reaching an estimated in length; a second, unnamed species, known only from three isolated premolar teeth, reached an estimated total body length of up to . Like other contemporary baleen whales of the Eocene, Llanocetus completely lacked baleen in its jaws. It was probably a suction feeder like the modern beaked and pygmy right whales.