Fossil records show that the first whales lived approximately 50 million years ago, according to Encyclopedia Britannica. Primitive whales, belonging to the extinct suborder Archaeoceti, had features in common with land mammals and were the ancestors of today's baleen and toothed whales.
Baleen whales use baleen plates within their mouths to filter plankton and other small animals from the surrounding water. The largest baleen whale, the blue whale, is the heaviest animal on Earth, weighing over 200 tons. Toothed whales use simple teeth to catch fish, squid and other animals. The sperm whale, the largest toothed whale, feeds on giant squid.