What is the first life form of a killer whale?

Killer whales, or orcas, are marine mammals belonging to the dolphin family, Delphinidae. They evolved from terrestrial ancestors that adapted to life in the ocean around 20 million years ago. The earliest life forms that eventually led to killer whales were likely small, land-dwelling mammals that gradually transitioned to aquatic environments, evolving features suited for marine life over millions of years.