Cetacea

About Cetacea

Cetacea is the mammalian order containing whales, dolphins and porpoises. Fossil and molecular evidence place it firmly inside Artiodactyla, the even-toed ungulates, with hippopotamuses as its closest living relatives — a grouping named Whippomorpha. The move from land to water is unusually well documented for so complete a transformation: a sequence of Eocene fossils from what is now Pakistan and India records a wolf-sized amphibious predator becoming an obligate swimmer over roughly fifteen million years.

Every living cetacean shares a suite of adaptations built on that history. The skull is telescoped so the nostrils sit on top of the head as a blowhole; the forelimbs are flippers with the finger bones still inside them; the hind limbs are gone, leaving a pair of unattached pelvic bones floating in muscle; and the tail ends in horizontal flukes that have no bony support at all. Blubber replaces fur for insulation, and countercurrent heat exchangers in the flippers and flukes let a warm-blooded animal live in near-freezing water.

Two suborders survive. Mysticeti feed by filtering prey through baleen; Odontoceti keep their teeth and hunt individual animals, navigating and finding them by echolocation. Around ninety living cetacean species are currently recognised. This atlas covers the ones conventionally called whales — all of the baleen whales, together with the sperm whales, beaked whales, beluga and narwhal — and leaves the oceanic dolphins, river dolphins and porpoises to a guide of their own.