Whales used to walk
Whales and dolphins are mammals that went back to the sea. Around fifty million years ago their ancestors were four-legged animals living near the shores of what is now Pakistan and India, about the size of a large dog. Over millions of years their legs shrank, their nostrils moved to the top of the head, and they became fully marine. The closest living relative of whales on land is the hippopotamus.
Like all mammals they breathe air, feed their young on milk and are warm-blooded, kept warm by a thick layer of BLUBBER. The blowhole is simply a nose on top of the head, and the spout of a whale is warm breath condensing in cold air. The call of a blue whale is among the loudest sounds made by any animal and can carry hundreds of kilometres underwater. Baleen whales, such as the blue whale, also build up a plug of earwax in layers, one pair a year, so scientists can count the layers to tell a whale's age, much like the rings of a tree.
The biggest animal that has ever lived
The BLUE WHALE is larger than any dinosaur: up to around thirty metres long and well over a hundred tonnes. Its heart alone can weigh around 180 kilograms. It feeds almost entirely on krill, straining them from huge mouthfuls of seawater through BALEEN plates, which are made of keratin, the same material as fingernails.
The SPERM WHALE has the largest brain of any animal and dives more than two kilometres deep to hunt squid, holding its breath for over an hour. The NARWHAL's long spiral tusk is actually a tooth, grown mostly by males, and it is packed with nerve endings. The ORCA, or killer whale, is the largest member of the dolphin family.
Songs that travel between oceans
Male HUMPBACK whales sing long, complex songs made of repeating phrases. All the males in one population sing the same song, and it slowly changes over each season. Scientists tracking humpbacks in the South Pacific have watched new songs spread from population to population across the ocean, like a hit record travelling from country to country.
Dolphins have signature whistles that work much like names: each BOTTLENOSE dolphin develops its own, and others use it to call that individual. Dolphins also sleep with only half the brain at a time, keeping the other half awake to breathe and watch for danger. A group of dolphins or whales is a POD.
Back from the brink
Commercial whaling killed millions of whales in the twentieth century, and several species came close to extinction. In 1986 an international ban on commercial whaling came into force. Some populations have recovered strongly since: humpbacks in several oceans have returned to numbers close to those before whaling.
The rest of the grid names more of them: the BELUGA, sometimes called the sea canary for its chirps, the MINKE, FIN WHALE, GRAY WHALE, RIGHT WHALE and BOWHEAD, the PILOT whale, the PORPOISE, and the RISSO, DUSKY and COMMON dolphins. When a whale leaps clear of the water it is said to BREACH, and it steers with each FLIPPER. Our oceans page covers the water they travel.