Temporal range: Late Miocene, 11.6–10 Ma
†M. elysius Kellogg, 1934 (type)
Mixocetus is a large-size mysticete with a long, narrow rostrum, a robust braincase, a nostril opening extending posteriorly just a few inches behind the antorbital processes, the posterior ends of the premaxillae, maxillae, and nasals tapering and extending posteriorly to a point between superior parts of supraorbital processes of the frontals, and a temporal fossa opening dorsally. Unlike Cetotherium, the antorbital process is larger, the lateral margins of the supraoccipital processes of the frontals are parallel to each other, there is a protruding lateral wall of the braincase, and the rear portion of the cranium has a very thick and posteriorly protruding exoccipital.
The holotype of this species is LACM 882. It was collected from the Modelo Formation (early Tortonian, 10-11.6 Ma) of Lincoln Heights in Los Angeles County, California. It now resides as a permanent exhibit at the Natural History Museum of Los Angeles County in Exposition Park, Los Angeles.
- R. Kellogg. 1934. A new cetothere from the Modelo Formation at Los Angeles, California. Carnegie Institution of Washington 447:83-104
- V. Bouetel and C. Muizon. 2006. The anatomy and relationships of Piscobalaena nanna (Cetacea, Mysticeti), a Cetotheriidae s.s. from the early Pliocene of Peru. Geodiversitas 28(2):319-395
- M. D. Uhen, R. E. Fordyce, and L. G. Barnes. 2008. Odontoceti. In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary Mammals of North America II:566-606