Ocean mammals are a diverse group of animals that live in the ocean, including whales. Whales are the largest of all ocean mammals and are divided into two main groups: baleen whales and toothed whales. Baleen whales, such as blue whales, have baleen plates instead of teeth and feed on small organisms like krill. Toothed whales, such as sperm whales, have teeth and feed on larger prey like fish and squid. Both types of whales use echolocation to navigate and communicate underwater.