The oldest "toothed" baleen whale (Mysticeti: Aetiocetidae) in the Northern Hemisphere

The origin and early evolution of baleen whales (Mysticeti, the largest extant vertebrates) have been linked to the inception of the Antarctic Circumpolar Current (ACC) at the Eocene-Oligocene boundary, and the only described Eocene mysticetes were found in the Southern Hemisphere (Antarctica, Peru), supporting this hypothesis. Here we describe a new mysticete, Fucaia humilis sp. nov., from strata in Washington State, USA, spanning the Eocene/Oligocene transition and corroborating a previously suspected early evolution of mysticetes in the Northern Hemisphere. Our results suggest a much earlier phase of mysticete radiation (>34 million years ago) across the globe during the Eocene. We hypothesize the origin and development of a relatively stable, nutrient-rich kelp ecosystem in the Eocene/Oligocene may have fostered the radiation of toothed mysticetes in the North Pacific basin.