A Dusky Dolphin.
Cetacea is an order from the Mammalia class. This group includes the marine mammals commonly known as whales, dolphins, and porpoises.Some species are noted for their high intelligence.
Cetaceans are the mammals best adapted to aquatic life. Their body is fusiform (spindle-shaped). The forelimbs are modified into flippers. The tiny hindlimbs are vestigial; they do not attach to the backbone and are hidden within the body. The tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated from the cooler water they inhabit by a thick layer of blubber.
Suborder Mysticeti, Baleen whales Suborder Odontoceti, Toothed whales Suborder †Archaeoceti, Ancient whales
|Balaenidae is a family of whales of the suborder mysticete that contains two living genera. Balaenids are large whales, with an average adult length of 15 to 17 metres (45–50 feet), and weighing 50-80 tonnes.Their principle distinguishing feature is their narrow, arched, upper jaw, which gives the animals a deeply curved jawline.|
|Rorquals(family Balaenopteridae) are the largest group of baleen whales, with nine extant species in two genera. They include the largest animal that has ever lived, the blue whale, which can reach 180 tonnes (200 short tons), and the fin whale, which reaches 120 tonnes (130 short tons); even the smallest of the group, the northern minke whale, reaches 9 tonnes (9.9 short tons).|
|Eschrichtiidae is a family of baleen whales in the suborder Mysticeti. Only one species is still extant, the Gray Whale, Eschrichtius robustus. However, the family also includes the fossil genera Archaeschrichtius from the Miocene and Eschrichtioides from the Pliocene of Italy and Gricetoides from the Pliocene of North Carolina.|
|Cetotheriidae is a family of baleen whales in the suborder Mysticeti. The family was generally thought to have existed from the Late Oligocene to the Late Pliocene before going extinct.|
|Oceanic dolphins are members of the cetacean family Delphinidae. They are found worldwide, mostly in the shallower seas of the continental shelves. As the name implies, these dolphins tend to be found in the open seas, unlike the river dolphins, although a few species such as the Irrawaddy dolphin are coastal or riverine.|
|The cetacean family Monodontidae comprises two unusual whale species, the narwhal, in which the male has a long tusk, and the white beluga whale. They are native to coastal regions and pack ice around the Arctic Sea, and the far north of the Atlantic and Pacific Oceans.|
|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 shorter beaks and flattened, spade-shaped teeth distinct from the conical teeth of dolphins.|
|Physeteroidea is a superfamily including just three living species of whale. In the past, these genera have sometimes been united in a single family, Physeteridae, with the two Kogia species in a subfamily (Kogiinae); however, recent practice is to allocate the genus Kogia to its own family, Kogiidae.|
|Iniidae is a family of river dolphins containing one living and three extinct genera.|
|The baiji was a freshwater dolphin found only in the Yangtze River in China. Nicknamed "Goddess of the Yangtze" in China, the dolphin is also called Chinese river dolphin, Yangtze River dolphin, whitefin dolphin and Yangtze dolphin. It is not to be confused with the Chinese white dolphin or the finless porpoise.|
|The La Plata dolphin or Franciscana (Pontoporia blainvillei) is found in coastal Atlantic waters of southeastern South America. Taxonomically, it is a member of the river dolphin group and the only one that actually lives in the ocean and saltwater estuaries, rather than inhabiting exclusively freshwater systems.|
|The Ganges and Indus River dolphin (Platanista gangetica) is a freshwater or river dolphin found in India, Bangladesh, Nepal and Pakistan which is split into two subspecies, the Ganges river dolphin (P. g. gangetica) and Indus river dolphin (P. g. minor).|
|Beaked whales are the members of the family Ziphiidae which consists of 21 species. These toothed whales are notable for their elongated beaks. Beaked whales are some of the world’s most extreme divers. They can dive for long periods.|