Whales live entire lives at sea—from birth to suckling
As a colloquial label, whales cover the larger fully aquatic placental mammals of Cetacea. They feed, mate, calve, and nurse offshore. Size spans roughly 2.6 m and 135 kg dwarfs up to the blue whale. Baleen plates sieve krill; toothed whales grab fish and squid with conical teeth and keen hearing.
"Whale" is an everyday label rather than a tidy branch of the tree: it covers the large cetaceans and leaves out dolphins and porpoises, which makes the informal group paraphyletic. Six oceanic dolphins nonetheless carry the word, including the orca and both pilot whales. Cetaceans are even-toed ungulates whose nearest living relatives are hippos, and the word itself descends from Old English hwæl, with no link to Wales.
Their ancestors walked. Early cetaceans entered the sea about 49 million years ago and became fully aquatic 5 to 10 million years later, gaining jaw-to-ear hearing, tail flukes, blowholes and flippers along the way while the hind legs shrank away. Around 34 million years ago the line split into baleen whales and toothed whales. Baleen whales strain krill through keratin plates, with heads that can make up 40% of body mass and pleated throats that balloon open; toothed whales seize prey with cone-shaped teeth, and their hearing is acute enough that some can survive blindness.
Every stage of life happens at sea. Whales surface to breathe through blowholes, two in baleen whales and one in toothed species, and a humpback's lungs hold about 5,000 litres. Sperm whales can stay under for up to 90 minutes. Blubber as thick as 28 cm in polar species can account for half the body weight, insulating the animal and fuelling long fasts, since humpbacks and blue whales migrate thousands of miles to warmer waters to give birth without feeding. Some mothers nurse calves for one to two years.
Sizes run from the dwarf sperm whale, 2.6 m and 135 kg, to the blue whale, around 30 m and 190 tonnes, the largest animal known ever to have lived; the sperm whale is the biggest toothed predator. Once hunted relentlessly, whales now have legal protection, though North Atlantic right whales fell to about 450 animals and the North Pacific grey whale is Critically Endangered.
Source: Whale
