Toothed whale

The toothed whales (systematic name Odontoceti) form a parvorder of the artiodactyl infraorder Cetacea, including sperm whales, beaked whales, dolphins, and porpoises. As the name suggests, the parvorder is characterized by the presence of teeth rather than the baleen of other whales. Seventy-three species of toothed whales are described. They are thought to have split from baleen whales, parvorder Mysticeti, around 34 million years ago. Whales and dolphins, the paraphyletic groups of Cetacea, as well as porpoises, belong to the clade Cetartiodactyla with even-toed ungulates; their closest living relatives are the hippopotamuses which diverged about 40 million years ago.

Toothed whales range in size from the 4.5 ft (1.4 m) and 120 lb (54 kg) vaquita to the 12-to-20 m (39-to-66 ft) and 11-to-55 t (12-to-61-short-ton) sperm whale. Several species of odontocetes exhibit sexual dimorphism, in that the females are larger than males. They have streamlined bodies and two limbs that are modified into flippers. Some can travel at up to 20 knots. Odontocetes have conical teeth designed for catching fish or squid. They have well-developed hearing, that is well adapted for both air and water, so much so that some can survive even if they are blind. Some species are well adapted for diving to great depths. Almost all have a layer of fat, or blubber, under the skin to keep warm in the cold water, with the exception of river dolphins.