Denebola brachycephala

Denebola brachycephala is an extinct whale of the family Monodontidae and the only known species of the genus Denebola, which should not be confused with the star of the same name. It was described by Barnes in 1984 from a fossil found on the Baja California peninsula in Mexico. Wikipedia calls it the earliest known ancestor of the beluga, Delphinapterus leucas, and dates it to the Upper Miocene; the Paleobiology Database places it in the Messinian age between about 7.2 and 5.3 million years ago, with one recorded occurrence. Because the fossil came from the Baja California peninsula, it is taken as a sign that the family once lived in warmer waters than the Arctic ones the living narwhal and beluga inhabit.