What is "cetacea"

Cetacea \Ce*ta"ce*a\, n. pl. [NL., from L. cetus whale, Gr. ?.] (Zo["o]l.) An order of marine mammals, including the whales. Like ordinary mammals they breathe by means of lungs, and bring forth living young which they suckle for some time. The anterior limbs are changed to paddles; the tail flukes are horizontal. There are two living suborders:

1. The {Mysticete or whalebone whales, having no true teeth after birth, but with a series of plates of whalebone [see Baleen.] hanging down from the upper jaw on each side, thus making a strainer, through which they receive the small animals upon which they feed.}

2. The {Denticete, including the dolphins and sperm whale, which have teeth. Another suborder ( Zeuglodontia) is extinct. The Sirenia were formerly included in the Cetacea, but are now made a separate order.}

order of marine mammals containing whales, 1830, Modern Latin, from Latin cetus "any large sea creature" (whales, seals, dolphins), from Greek ketos "a whale, a sea monster," which is of unknown origin, + -acea. Hence cetology "the study of whales," first attested 1851 in "Moby Dick."

n. Whale-like mammals.

Cetacea , (from Latin cetus " whale" and Greek ketos "huge-fish") are a widely distributed and diverse clade of carnivorous, finned, aquatic marine mammals. They comprise the extant parvorders Odontoceti (toothed whales including dolphins and porpoises), Mysticeti (the baleen whales), and Archaeoceti (the ancestors of modern whales, and now extinct). There are around 89 species of cetaceans, and more than 70 belonging to Odontoceti. While cetaceans were historically thought to have descended from mesonychids, molecular evidence supports them as a relative of Artiodactyls (even-toed ungulates). Cetaceans belong to the order Cetartiodactyla (formed by combining Cetacea + Artiodactyla) and their closest living relatives are hippopotamuses and other hoofed mammals ( camels, pigs, and ruminants), having diverged about 50 million years ago.

Cetaceans range in size from the and Maui's dolphin to the and blue whale, which is also the largest creature alive. Several species exhibit sexual dimorphism. They have streamlined bodies and two (external) limbs that are modified into flippers. Though not as flexible or agile as seals, cetaceans can swim very fast, with the killer whale able to travel at in short bursts and the fin whale able to cruise at . The hindlimbs of cetaceans are internal, and are thought to be vestigial. Dolphins are able to make very tight turns while swimming at high speeds. Baleen whales have short hairs on their mouth, unlike the toothed whales. Cetaceans have well-developed senses—their eyesight and hearing are adapted for both air and water, and baleen whales have a tactile system in their vibrissae. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water.

Although cetaceans are widespread, most species prefer the colder waters of the Northern and Southern Hemispheres. They spend their lives in the water, having to mate, give birth, molt or escape from predators, like killer whales, underwater. This has drastically affected their anatomy to be able to do so. They feed largely on fish and marine invertebrates; but a few, like the killer whale, feed on large mammals and birds, such as penguins and seals. Some baleen whales (mainly gray whales and right whales) are specialised for feeding on benthic creatures. Male cetaceans typically mate with more than one female ( polygyny), although the degree of polygyny varies with the species. Cetaceans are not shown to have pair bonds. Male cetacean strategies for reproductive success vary between herding females, defending potential mates from other males, or whale song which attracts mates. Calves are typically born in the fall and winter months, and females bear almost all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively short period of time, which is more typical of baleen whales as their main food source (invertebrates) aren't found in their breeding and calving grounds ( tropics). Cetaceans produce a number of vocalizations, notably the clicks and whistles of dolphins, the moaning songs of the humpback whale.

The meat, blubber and oil of cetaceans have traditionally been used by indigenous peoples of the Arctic. Cetaceans have been depicted in various cultures worldwide. Dolphins are commonly kept in captivity and are even sometimes trained to perform tricks and tasks, other cetaceans aren't as often kept in captivity (with usually unsuccessful attempts). Once relentlessly hunted by commercial industries for their products, cetaceans are now protected by international law. The baiji (Chinese river dolphin) has become extinct in the past century, while the vaquita and Yangtze finless porpoise are ranked Critically Endangered by the International Union for Conservation of Nature. Besides hunting, cetaceans also face threats from accidental trapping, marine pollution, and ongoing climate change.