Data from: A new basal chaeomysticete (Mammalia: Cetacea) from the late Oligocene Pysht Formation of Washington, USA

Modern baleen-bearing mysticetes are descendant from archaic, toothed
mysticetes known from the Late Eocene and Oligocene of the Pacific Ocean.
These toothed mysticetes, such as aetiocetids and mammalodontids, dominate
the Oligocene fossil record. However, larger bodied eomysticetids have
recently been described from the Oligocene of the Pacific and western
Atlantic. These eomysticetids lack functional teeth as adults and are thus
considered to be the earliest members of Chaeomysticeti. A new fossil from
the Olympic Peninsula, Washington State, including a partial skull,
tympanic bullae, mandibles and postcrania, is here described as Sitsqwayk
cornishorum gen. et sp. nov. S. cornishorum is a Late Oligocene mysticete
lacking functional teeth and is the most phylogenetically basal
chaeomysticete. Accordingly, S. cornishorum exhibits a mosaic of
aetiocetid and eomysticetid characteristics. The presence of S.
cornishorum in the North Pacific, and its phylogenetic position relative
to the eomysticetids from the Southern Ocean, suggests a possible a North
Pacific point of origin for Chaeomysticeti.