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Temporal range: Late Oligocene
Aetiocetus BW.jpg
Aetiocetus cotylalveus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Mysticeti
Family: Aetiocetidae
Emlong 1966
Genus: Aetiocetus
Emlong 1966

Aetiocetus is a genus of extinct baleen whale that lived 33.9 to 23.03 million years ago, in the Oligocene in the North Pacific, around Japan, Mexico, and Oregon, U.S. It was named by Douglas Emlong in 1966 and currently contains four species, A. cotylalveus, A. polydentatus, A. tomitai, and A. weltoni.[1]


Aetiocetus is a transitional form between early whales such as Dorudontinae and modern baleen whales. It shares a number of cranial details with late archaeocetes, most notably the retention of a heterodont adult dentition and the location of the blowhole halfway up the snout, but also a rigid rostrum and a dentary with a large coronoid process positioned in the temporal fossa (the holes at the back of the skull). To some extent, Aetiocetus shares several of these primitive features with Eomysticetus, a more derived toothless stem mysticete, but both these genera also share features unique to mysticetes, including a wide mouth that lack teeth in the back and outwardly bowed dentaries loosely connected in front by a kinetic joint.[2]

Aetiocetus skulls have also shown the animal bore a full set of teeth, as well as baleen.[3] Aetiocetus weltoni (no dentaries are preserved for A. cotylalveus) has 11 upper and 12 lower teeth on each side (I1–3, C, P1–8; I1–3, C, P1–4, M1–3).[4] The teeth of A. weltoni and A. cotylalveus are near-monodont while those of A. polydentatus displays a higher degree of polydonty.[5] Aetiocetus most likely fed on fish and crustaceans.[6]

Douglas Emlong originally classified it in the extinct whale suborder Archaeoceti, because of its teeth. However, when Van Valen analyzed it in 1968, he moved the genus to the suborder Mysticeti due to its derived pattern of bone telescoping.[7][8]

The other genera in the family Aetiocetidae are Ashorocetus, Chonecetus, Morawanocetus, and Willungacetus.[1] All aetiocetids are known from the North Pacific except the Australian Willungacetus and its taxonomy is disputed.[9]

See also[edit]



  1. ^ a b "Aetiocetus". Fossilworks. Retrieved January 2014. 
  2. ^ Deméré & Berta 2008, Aetiocetids as transitional taxa, pp. 339–340
  3. ^ Deméré et al. 2008, See Fig. 1
  4. ^ Deméré & Berta 2008, pp. 334, 336
  5. ^ Deméré & Berta 2008, p. 339
  6. ^ Wallace 2007[page needed]
  7. ^ Deméré & Berta 2008, p. 309
  8. ^ Hoelzel 2002, p. 61
  9. ^ Deméré & Berta 2008, p. 308


  • Barnes, L. G.; Kimura, M.; Furusawa, H.; Sawamura, H. (1995). "Classification and distribution of Oligocene Aetiocetidae (Mammalia; Cetacea; Mysticeti) from western North America and Japan". The Island Arc 3 (4): 392–431. doi:10.1111/j.1440-1738.1994.tb00122.x. Lay summary (December 2013). 
  • Emlong, D. (1966). "A new archaic cetacean from the Oligocene of Northwest Oregon". Bulletin of the Museum of Natural History, University of Oregon 3: 1–51. Lay summary (January 2014). 
  • Deméré, T. A.; Berta, A. (2008). "Skull anatomy of the Oligocene toothed mysticete Aetioceus weltoni (Mammalia; Cetacea): implications for mysticete evolution and functional anatomy". Zoological Journal of the Linnean Society 154 (2): 308–352. doi:10.1111/j.1096-3642.2008.00414.x. 
  • Deméré, T. A.; McGowen, M. R.; Berta, A.; Gatesy, J. (2008). "Morphological and Molecular Evidence for a Stepwise Evolutionary Transition from Teeth to Baleen in Mysticete Whales". Systematic Biology 57 (1): 15–37. doi:10.1080/10635150701884632. 
  • Hoelzel, A. Rus (2002). Marine Mammal Biology: An Evolutionary Approach. Blackwell Publishing. ISBN 0-632-05232-5. 
  • Wallace, D. R. (2007). Neptune's Ark: From Ichthyosaurs to Orcas. University of California Press. ISBN 0-520-24322-6.