A new stem odontocete from the late Oligocene Pysht Formation in Washington State, U.S.A.

Odontocetes first appear in the fossil record during the early Oligocene and soon after show a near-worldwide distribution. However, little is still known of their early diversity, especially in the North Pacific Region. A new taxon of stem odontocete with heterodont dentition, <i>Olympicetus avitus</i>, gen. et sp. nov., is described herein from the upper Oligocene Pysht Formation in Washington State, U.S.A. The material consists of two partial skulls belonging to a juvenile and a neonate and includes part of the dentition and a tympanic bulla. <i>Olympicetus</i> shares many similarities with the Oligocene odontocetes <i>Simocetus rayi</i> and <i>Ashleycetus planicapitis</i> but displays a combination of characters that distinguish it from these and other coeval taxa. A phylogenetic analysis shows <i>Olympicetus</i> in a polytomy with Xenorophidae, a clade of early high-frequency-hearing odontocetes mainly known from the western Atlantic. Furthermore, <i>Olympicetus</i> displays characters that can be considered as structural proxies for echolocation, such as having premaxillary sac fossae and the maxilla expanded over the frontal. In addition to <i>Olympicetus</i>, other marine tetrapods from the Pysht Formation include marine birds, desmostylians, pinnipeds, and early mysticetes, giving us a unique insight into late Oligocene marine tetrapod faunas of the North Pacific. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP http://zoobank.org/urn:lsid:zoobank.org:pub:F58AE47A-DBDF-41F0-980D-859ECEF87316 Citation for this article: Vélez-Juarbe, J. 2017. A new stem odontocete from the late Oligocene Pysht Formation in Washington State, U.S.A. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1366916.