English

Noun

porpoises

1. Plural of porpoise

Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen. The most obvious visible difference between the two groups is that porpoises have flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and their shorter beaks.

The name derives from French pourpois, originally from Medieval Latin porcopiscus (porcus pig + piscus fish).

Porpoises, divided into six species, live in all oceans, mostly near the shore. Freshwater populations of the Finless Porpoise also exist. Probably the best known species is the Harbour Porpoise, which can be found across the Northern Hemisphere. Like all toothed whales, porpoises are predators, using sounds to locate prey and to coordinate with others. They hunt fish, squid, and crustaceans.

Porpoises apparently diverged from dolphins about 15 million years ago in the northern Pacific, then spread across the globe much later.

Taxonomy and evolution

Porpoises, along with whales and dolphins, are descendants of land-living ungulates (hoofed animals) that first entered the oceans around 50 million years ago. During the Miocene (23 to 5 MYA), mammals were fairly modern. The cetaceans diversified, and fossil evidence suggests that porpoises diverged from dolphins and other cetaceans around 15 MYA. The oldest fossils are known from the shallow seas around the north Pacific, with animals spreading to the European coasts and southern hemisphere only much later, during the Pliocene.

• Sub-order Odontoceti: toothed whales
  • Family Phocoenidae: Porpoises
    • Genus Neophocaena
      • Finless Porpoise, Neophocaena phocaeniodes
    • Genus Phocoena
      • Harbour Porpoise, Phocoena phocoena
      • Vaquita, Phocoena sinus
      • Spectacled Porpoise, Phocoena dioptrica
      • Burmeister's Porpoise, Phocoena spinipinnis
    • Genus Phocoenoides
      • Dall's Porpoise, Phocoenoides dalli

Recently-discovered hybrids between male Harbour porpoises and female Dall's Porpoises indicate that the two species may actually be members of the same genus.

These animals are the smallest cetaceans, reaching body lengths up to 2.5 metres (8 ft); the smallest species is the Vaquita, reaching up to 1.5 m (5 ft). In terms of weight the lightest is the Finless Porpoise at 30-45 kilograms (65-100 lb) and the heaviest is Dall's Porpoise at 130-200 kg (280-440 lb). Because of their small size, porpoises lose body heat to the water more rapidly than other cetaceans. Their stout shape, which minimizes surface area, may be an adaptation to reduce heat loss. Thick blubber also insulates them from the cold. The small size of porpoises requires them to eat frequently, rather than depending on fat reserves.

In some countries, porpoises are hunted for food or bait meat.

Porpoises are rarely held in captivity in zoos or oceanaria, as they are generally not as capable of adapting to tank life nor as easily trained as dolphins.

See also

• Dolphin
• Whale

References

External links

• Whale and Dolphin Conservation Society (WDCS)