Most cetaceans have triangular teeth and feed on fish or squid. These include dolphins, porpoise’s narwhals and sperm whales. A number of whales, including most of the largest, feed by filtering crustations and shoaling fish through large plates of bristles called baleen.
The baleen whales open their mouths to let water in. They then raise their tongue to force the water out. As the water passes through the bristles, they retain any animal which the whale then swallows. Baleen whale embryos have teeth which show they evolved from toothed ancestors.