The first oceanic dolphins such as kentriodonts, evolved in the late Oligocene and diversified greatly during the mid-Miocene. The first fossil cetaceans near shallow seas (where porpoises inhabit) were found around the North Pacific; species like "Semirostrum" were found along California (in what were then estuaries). These animals spread to the European coasts and Southern Hemisphere only much later, during the Pliocene. The earliest known ancestor of arctic whales is "Denebola brachycephala" from the late Miocene around 9–10 million years ago. A single fossil from Baja California indicates the family once inhabited warmer waters.