Cetacea (Whales, Porpoises and Dolphins)

Abstract

Abstract Whales and dolphins (cetaceans) are streamlined mammals that spend all their lives in water. Their earliest ancestors evolved more than 50 million years ago from even‐toed hoofed mammals like hippos and cows. Modern cetaceans range through all oceans and from the tropics to the polar regions. Even so, they belong to just two major clades: baleen whales (mysticetes) and toothed whales (odontocetes). Mysticetes include the largest animals on Earth and are characterised by keratinous, comb‐like baleen plates which they use to filter feed on tiny prey. By contrast, odontocetes use a form of biosonar (echolocation) to target single fish and squid. The vast majority of the 92 recognised living species belong to just three families: oceanic dolphins, beaked whales and rorquals. Key Concepts Whales and dolphins evolved from even‐toed hoofed mammals. They spend all their lives in water and show key aquatic adaptations like streamlined bodies, baleen, echolocation and suction feeding. They include the largest and, apart from humans, the brainiest animals on Earth. Most belong to just three major families: oceanic dolphins, beaked whales and rorquals. Advances in fossil sampling are beginning to reveal global patterns in whale evolution, including a major turnover event around 23 Ma.