Mixocetus

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.