Porpoises are small cetaceans closer to narwhals than to dolphins
Porpoises (Phocoenidae) look dolphin-like yet relate more closely to narwhals and belugas. Eight living species are among the smallest toothed whales, from the 1.4 m, 54 kg vaquita to Dall’s porpoise at 2.3 m and 220 kg. Some females outgrow males.
Porpoises make up the family Phocoenidae, eight living species that rank among the smallest toothed whales. They resemble dolphins but are closer kin to narwhals and belugas. Two features usually give them away: flattened, spade-shaped teeth instead of the cone-shaped teeth of dolphins, and no prominent beak, though a few dolphins such as Hector's dolphin also lack one. Like all cetaceans, they belong with the even-toed hoofed mammals in the clade Cetartiodactyla.
The vaquita is the smallest at 1.4 metres and 54 kg; Dall's porpoise is the largest at 2.3 metres and 220 kg. In several species females outgrow males. Their streamlined bodies carry two flippers and a warming layer of blubber, some are strong deep divers, and they rely mainly on echolocation, using ultrasonic clicks both to navigate and to communicate. Unlike many dolphins they do not travel in large groups. They eat mostly fish and squid, and under good conditions a female may calve every year, usually in spring or summer, with the calf dependent until the next spring.
They live in rivers, like the finless porpoise, in coastal and shelf waters, like the harbour porpoise and vaquita, and in the open ocean, like Dall's and the spectacled porpoise, from the tropical Sea of Cortez to polar Greenland. Their ancestors were land-dwelling hoofed mammals that entered the sea about 50 million years ago, and porpoises split from dolphins roughly 15 million years ago. The oldest fossils come from shallow North Pacific seas, with spread to Europe and the Southern Hemisphere only in the Pliocene. Dall's and harbour porpoises are sister species and are known to hybridise.
Some countries still drive-hunt porpoises, but gillnet bycatch, competition with fisheries and pollution by heavy metals and organochlorines are bigger threats. Gillnets have pushed the vaquita to the brink, with fewer than a dozen predicted to survive, making it the most endangered cetacean since the baiji's extinction.
Source: Porpoise
