Temporal range: Late Oligocene
Aetiocetus is an extinct genus of baleen whale that lived 25 million years ago, in the Oligocene period. Its fossils have been found in the North Pacific, around Oregon. It was first named by Douglas Emlong in 1966 and currently contains four species, A cotylalveus, A. polydentatus, A. tomitai, and A. weltoni.
Aetiocetus is a transitional fossil between early whales and modern whales, its blowhole being located halfway up its snout rather than at the top of its head. It is also one of the earliest known baleen whales. The genus, though more cranially reminiscent of archaic whales, with its pronounced snout and flat cranium, had a loose jaw like later baleen whales. Aetiocetus skulls have also shown the animal bore a full set of teeth, as well as baleen. The skulls contain about 44 teeth, which consist of cusped molars, curved canines, and incisors. Aetiocetus most likely fed on fish and crustaceans.
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. Other genera in the same family, Aetiocetidae, include Ashorocetus, Chonecetus, Morawanocetus and Willungacetus.
- A. cotylalveus Emlong, 1966 (type species)
- A. polydentatus Sawamura, 1994
- A. tomitai Kimura & Barnes, 1994
- A. weltoni Barnes & Kimura, 1994 – an analysis of this species revealed similar palatal nutrient foramina to those that house vessels that feed modern genera of Mysticeti.
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