Aetiocetidae Explained

Aetiocetidae is an extinct family of toothed baleen whales known from the Oligocene and latest Eocene, so far only from rocks deposited in the North Pacific Ocean.^{[1] [2] [3]} The whales ranged in size from 3to long. Many of the described specimens were discovered from the Upper Oligocene of the Japanese Morawan Formation, the largest known one from the Morawan's Upper tuffaceous siltstone. Other formally described extinct toothed mysticetis from this time are smaller, from 3to in length. Mysticeti with true baleen are seen in fossils from the Upper Oligocene. The monophyly of the family is still uncertain, as are the evolutionary relationship between the early toothed baleen whales (Aetiocetidae, Mammalodontidae, and Llanocetidae) and the early and extant edentulous baleen whales.^[4] However, the cladistic analyses of Coronodon and Mystacodon seem to indicate that Aetiocetidae and Llanocetidae are more closely related to crown Mysticeti than to Mammalodontidae, Coronodon, and Mystacodon.^{[5] [6]}

Notes and References

1. Book: Prothero. Donald R.. Berggren. William A.. Eocene-Oligocene Climatic and Biotic Evolution. 2014. Princeton University Press. 9780691604954. 371. 18 Cetacean Evolution and Eocene/Oligocene Environments.
2. Tsai. Cheng-Hsiu. Ando. Tatsuro. Niche Partitioning in Oligocene Toothed Mysticetes (Mysticeti: Aetiocetidae). Journal of Mammalian Evolution. 14 April 2015. 10.1007/s10914-015-9292-y. 23. 33–41.
3. Tsai, C.-H., Goedert, J.L., and Boessenecker, R.W. 2024. The oldest mysticete in the Northern Hemisphere. Current Biology 34:P1794-1800.E3. https://doi.org/10.1016/j.cub.2024.03.11
4. Marx. Felix G.. The More the Merrier? A Large Cladistic Analysis of Mysticetes, and Comments on the Transition from Teeth to Baleen. Journal of Mammalian Evolution. 25 September 2010. 18. 2. 77–100. 10.1007/s10914-010-9148-4.
5. Lambert . Olivier . Martínez-Cáceres . Manuel . Bianucci . Giovanni . Di Celma . Claudio . Salas-Gismondi . Rodolfo . Steurbaut . Etienne . Urbina . Mario . de Muizon . Christian . 2017 . Earliest Mysticete from the Late Eocene of Peru Sheds New Light on the Origin of Baleen Whales . Current Biology . 27. 1535–1541.e2. 10.1016/j.cub.2017.04.026 . free . 28502655 . 11581/396095 . free .
6. Geisler . Jonathan H . Boessenecker . Robert W . Brown . Mace . Beatty . Brian L . 2017 . The Origin of Filter Feeding in Whales . Current Biology . 27 . 13. 2036–2042 . 10.1016/j.cub.2017.06.003 . 28669761 . free .