The oldest mysticete in the Northern Hemisphere

Extant baleen whales (Mysticeti) uniquely use keratinous baleen for filter-feeding and lack dentition, but the fossil record clearly shows that "toothed" baleen whales first appeared in the Late Eocene.1Lambert O. Martínez-Cáceres M. Bianucci G. Di Celma C. Salas-Gismondi R. Steurbaut E. Urbina M. de Muizon C. Earliest mysticete from the Late Eocene of Peru sheds new light on the origin of baleen whales.Curr. Biol. 2017; 27: 1535-1541.e2https://doi.org/10.1016/j.cub.2017.04.026Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar Globally, only two Eocene mysticetes have been found, and both are from the Southern Hemisphere: Mystacodon selenensis from Peru, 36.4 mega-annum (Ma) ago1Lambert O. Martínez-Cáceres M. Bianucci G. Di Celma C. Salas-Gismondi R. Steurbaut E. Urbina M. de Muizon C. Earliest mysticete from the Late Eocene of Peru sheds new light on the origin of baleen whales.Curr. Biol. 2017; 27: 1535-1541.e2https://doi.org/10.1016/j.cub.2017.04.026Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar,2de Muizon C. Bianucci G. Martínez-Cáceres M. Lambert O. Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations.Geodiversitas. 2019; 41: 401-499https://doi.org/10.5252/geodiversitas2019v41a11Crossref Scopus (30) Google Scholar and Llanocetus denticrenatus from Antarctica, 34.2 Ma ago.3Fordyce R.E. Marx F.G. Gigantism precedes filter feeding in baleen whale evolution.Curr. Biol. 2018; 28: 1670-1676.e2https://doi.org/10.1016/j.cub.2018.04.027Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar,4Mitchell E.D. A new cetacean from the late Eocene La Meseta Formation Seymour Island, Antarctic peninsula.Can. J. Fish. Aquat. Sci. 1989; 46: 2219-2235https://doi.org/10.1139/f89-273Crossref Scopus (137) Google Scholar Based on a partial skull from the lower part of the Lincoln Creek Formation in Washington State, USA, we describe the Northern Hemisphere's geochronologically earliest mysticete, Fucaia humilis sp. nov. Geology, biostratigraphy, and magnetostratigraphy places Fucaia humilis sp. nov. in the latest Eocene (ca. 34.5 Ma ago, near the Eocene/Oligocene transition at 33.9 Ma ago), approximately coeval with the oldest record of fossil kelps, also in the northeastern Pacific.5Kiel S. Goedert J.L. Huynh T.L. Krings M. Parkinson D. Romero R. Looy C.V. Early Oligocene kelp holdfasts and stepwise evolution of the kelp ecosystem in the North Pacific.Proc. Natl. Acad. Sci. USA. 2024; 121e2317054121https://doi.org/10.1073/pnas.2317054121Crossref Scopus (0) Google Scholar This observation leads to our hypothesis that the origin and development of a relatively stable, nutrient-rich kelp ecosystem5Kiel S. Goedert J.L. Huynh T.L. Krings M. Parkinson D. Romero R. Looy C.V. Early Oligocene kelp holdfasts and stepwise evolution of the kelp ecosystem in the North Pacific.Proc. Natl. Acad. Sci. USA. 2024; 121e2317054121https://doi.org/10.1073/pnas.2317054121Crossref Scopus (0) Google Scholar,6Starko S. Soto Gomez M.S. Darby H. Demes K.W. Kawai H. Yotsukura N. Lindstrom S.C. Keeling P.J. Graham S.W. Martone P.T. A comprehensive kelp phylogeny sheds light on the evolution of an ecosystem.Mol. Phylogenet. Evol. 2019; 136: 138-150https://doi.org/10.1016/j.ympev.2019.04.012Crossref PubMed Scopus (56) Google Scholar in the latest Eocene may have fostered the radiation of small-sized toothed mysticetes (Family Aetiocetidae) in the North Pacific basin, a stark contrast to the larger Llanocetidae (whether Mystacodon belongs to llanocetids or another independent clade remains unresolved) with the latest Eocene onset of the Antarctic Circumpolar Current in the Southern Hemisphere.7Ewan Fordyce R.E. The development of the Circum-Antarctic Current and the evolution of the Mysticeti (Mammalia: Cetacea).Palaeogeogr. Palaeoclimatol. Palaeoecol. 1977; 21: 265-271https://doi.org/10.1016/0031-0182(77)90038-4Crossref Scopus (34) Google Scholar,8Marx F.G. Uhen M.D. Climate, critters, and cetaceans: Cenozoic drivers of the evolution of modern whales.Science. 2010; 327: 993-996https://doi.org/10.1126/science.1185581Crossref PubMed Scopus (166) Google Scholar,9Steeman M.E. Hebsgaard M.B. Fordyce R.E. Ho S.Y. Rabosky D.L. Nielsen R. Rahbek C. Glenner H. Sørensen M.V. Willerslev E. Radiation of extant cetaceans driven by restructuring of the oceans.Syst. Biol. 2009; 58: 573-585https://doi.org/10.1093/sysbio/syp060Crossref PubMed Scopus (290) Google Scholar Our discovery suggests that disparate mechanisms and ecological scenarios may have nurtured contrasting early mysticete evolutionary histories in the Northern and Southern hemispheres.