Porpoise
| Porpoise Temporal range: 15.970–0 Ma Miocene to Recent |
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| The harbor porpoise (Phocoena phocoena) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Superfamily: | Delphinoidea |
| Family: |
Phocoenidae Gray, 1825 |
| Genera | |
Porpoises are a group of fully aquatic marine mammals that are sometimes referred to as mereswine, all of which are classified under the family Phocoenidae, parvorder (toothed whales). There are six extant species of porpoise. They are small toothed whales that are very closely related to oceanic dolphins. The most obvious visible difference between the two groups is that porpoises have shorter beaks and flattened, spade-shaped teeth distinct from the conical teeth of dolphins. Porpoises, and other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates, and their closest living relatives are the hippopotamuses, having diverged from them about 40 million years ago.
Porpoises range in size from the 1.4 metres (4.6 ft) and 54 kilograms (119 lb) vaquita, the smallest cetacean to be discovered, to the 2.3 metres (7.5 ft) and 220 kilograms (490 lb) Dall's porpoise. Several species exhibit sexual dimorphism in that the females are larger than males. They have streamlined bodies and two limbs that are modified into flippers. Dall's porpoise is one of the fastest cetaceans discovered, with the ability to travel at 41 knots (76 km/h). Porpoises have the ability to produce biosonar and it is their primary sensory system. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep them warm in cold water.
Porpoises are not very widespread, with many specialising near the polar regions, usually near the coast. Porpoises feed largely on fish and squid, much like the rest of the odontocetes. Males typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. Some porpoises produce a variety of clicks and whistles, which are thought to be primarily for social purposes. A few species, like the harbour porpoise, are highly sociable, but pods generally do not exceed ten individuals for most species.
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