The blue whale is the largest animal ever known to have lived, including all known dinosaurs.
Blue whales can exceed 30 metres in length and weigh more than 150 tonnes, although exact maximum measurements are difficult because very large carcasses are rarely measured intact. Their enormous size is supported by dense muscle, a large heart, and a highly efficient feeding system.
Despite their size, blue whales mainly eat tiny krill. They use expandable throat grooves to engulf huge volumes of seawater, then push the water through baleen plates with their tongues. The krill remain trapped and are swallowed.
Blue whales occur in oceans worldwide, usually in separate populations. Commercial whaling drastically reduced their numbers during the 20th century, and the species remains endangered. The fin whale is also exceptionally large, but it is generally smaller than the blue whale.