Dolphin is the common name of aquatic mammals within the infraorder Cetacea. The term dolphin usually refers to the extant families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), named Iniidae (the New World river dolphins), and Pontoporiidae (the brackish dolphins), and the extinct Lipotidae (baiji or Chinese river dolphin). There are 40 extant species named as dolphins.
Dolphins range in size from the relatively small 1.7-metre-long (5 ft 7 in) long and 50-kilogram (110-pound) bodied Maui's dolphin to the 9.5 m (31 ft 2 in) and 10-tonne (11-short-ton) killer whale. Dolphins can sometimes leap about 30 feet (9.1 m). Several species of dolphins exhibit sexual dimorphism, in that the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, some dolphins can travel at speeds 29 kilometres (18 mi) per hour for short distances.[1] Dolphins use their conical shaped teeth to capture fast-moving prey. They have well-developed hearing which is adapted for both air and water and is so well developed that some can survive even if they are blind. 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 dolphins are widespread, most species of them prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, like seals. Male dolphins 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. Mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in the form of clicks and whistles.
Dolphins are sometimes hunted in places such as Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they also face threats from bycatch, habitat loss, and marine pollution. Dolphins have been depicted in various cultures worldwide. Dolphins occasionally feature in literature and film, as in the film series Free Willy. Dolphins are sometimes kept in captivity and trained to perform tricks. The most common dolphin species in captivity is the bottlenose dolphin, while there are around 60 killer whales in captivity.
Etymology
The name is originally from Greek δελφίς (delphís), "dolphin",[2] which was related to the Greek δελφύς (delphus), "womb".[2] The animal's name can therefore be interpreted as meaning "a 'fish' with a womb".[3] The name was transmitted via the Latin delphinus[4] (the romanization of the later Greek δελφῖνος – delphinos[2]), which in Medieval Latin became dolfinus and in Old French daulphin, which reintroduced the ph into the word "Dolphin". The term mereswine (that is, "sea pig") has also historically been used.[5]
The term 'dolphin' can be used to refer to, under the parvorder Odontoceti, all the species in the family Delphinidae (oceanic dolphins) and the river dolphin families Iniidae (South American river dolphins), Pontoporiidae (La Plata dolphin), Lipotidae (Yangtze river dolphin) and Platanistidae (Ganges river dolphin and Indus river dolphin).[6][7] This term has often been misused in the US, mainly in the fishing industry, where all small cetaceans (dolphins and porpoises) are considered porpoises,[8] while the fish dorado is called dolphin fish.[9] In common usage the term 'whale' is used only for the larger cetacean species,[10] while the smaller ones with a beaked or longer nose are considered 'dolphins'.[11] The name 'dolphin' is used casually as a synonym for bottlenose dolphin, the most common and familiar species of dolphin.[12] There are six species of dolphins commonly thought of as whales, collectively known as blackfish: the killer whale, the melon-headed whale, the pygmy killer whale, the false killer whale, and the two species of pilot whales, all of which are classified under the family Delphinidae and qualify as dolphins.[13] Though the terms 'dolphin' and 'porpoise' are sometimes used interchangeably, porpoises are not considered dolphins and have different physical features such as a shorter beak and spade-shaped teeth; they also differ in their behavior. Porpoises belong to the family Phocoenidae and share a common ancestry with the Delphinidae.[12]
A group of dolphins is called a "school" or a "pod". Male dolphins are called "bulls", females called "cows" and young dolphins are called "calves".[14]
Taxonomy and distribution
- Parvorder Odontoceti, toothed whales
- Family Platanistidae
- Ganges and Indus river dolphin, Platanista gangetica with two subspecies
- Ganges river dolphin (or Susu), Platanista gangetica gangetica
- Indus river dolphin (or Bhulan), Platanista gangetica minor
- Ganges and Indus river dolphin, Platanista gangetica with two subspecies
- Family Iniidae
- Amazon river dolphin (or Boto), Inia geoffrensis
- Orinoco river dolphin (the Orinoco subspecies), Inia geoffrensis humboldtiana
- Araguaian river dolphin (Araguaian boto), Inia araguaiaensis
- Bolivian river dolphin, Inia boliviensis
- Amazon river dolphin (or Boto), Inia geoffrensis
- Family Lipotidae
- Baiji (or Chinese river dolphin), Lipotes vexillifer (possibly extinct, since December 2006)
- Family Pontoporiidae
- La Plata dolphin (or Franciscana), Pontoporia blainvillei
- Family Delphinidae, oceanic dolphins
- Genus Delphinus
- Long-beaked common dolphin, Delphinus capensis
- Short-beaked common dolphin, Delphinus delphis
- Genus Tursiops
- Common bottlenose dolphin, Tursiops truncatus
- Indo-Pacific bottlenose dolphin, Tursiops aduncus
- Burrunan dolphin, Tursiops australis, a newly discovered species from the sea around Melbourne in September 2011.[15]
- Genus Lissodelphis
- Northern right whale dolphin, Lissodelphis borealis
- Southern right whale dolphin, Lissodelphis peronii
- Genus Sotalia
- Genus Sousa
- Indo-Pacific humpback dolphin, Sousa chinensis
- Chinese white dolphin, Sousa chinensis chinensis
- Atlantic humpback dolphin, Sousa teuszii
- Indo-Pacific humpback dolphin, Sousa chinensis
- Genus Stenella
- Atlantic spotted dolphin, Stenella frontalis
- Clymene dolphin, Stenella clymene
- Pantropical spotted dolphin, Stenella attenuata
- Spinner dolphin, Stenella longirostris
- Striped dolphin, Stenella coeruleoalba
- Genus Steno
- Rough-toothed dolphin, Steno bredanensis
- Genus Cephalorhynchus
- Chilean dolphin, Cephalorhynchus eutropia
- Commerson's dolphin, Cephalorhynchus commersonii
- Haviside's dolphin, Cephalorhynchus heavisidii
- Hector's dolphin, Cephalorhynchus hectori
- Genus Grampus
- Risso's dolphin, Grampus griseus
- Genus Lagenodelphis
- Fraser's dolphin, Lagenodelphis hosei
- Genus Lagenorhynchus
- Atlantic white-sided dolphin, Lagenorhynchus acutus
- Dusky dolphin, Lagenorhynchus obscurus
- Hourglass dolphin, Lagenorhynchus cruciger
- Pacific white-sided dolphin, Lagenorhynchus obliquidens
- Peale's dolphin, Lagenorhynchus australis
- White-beaked dolphin, Lagenorhynchus albirostris
- Genus Orcaella
- Australian snubfin dolphin, Orcaella heinsohni
- Irrawaddy dolphin, Orcaella brevirostris
- Genus Peponocephala
- Melon-headed whale, Peponocephala electra
- Genus Orcinus
- Killer whale (orca), Orcinus orca
- Genus Feresa
- Pygmy killer whale, Feresa attenuata
- Genus Pseudorca
- False killer whale, Pseudorca crassidens
- Genus Globicephala
- Long-finned pilot whale, Globicephala melas
- Short-finned pilot whale, Globicephala macrorhynchus
- Genus †Australodelphis
- †Australodelphis mirus
- Genus Delphinus
- Family Platanistidae
- Six species in the family Delphinidae are commonly called "whales", but genetically are dolphins. They are sometimes called blackfish.
- Melon-headed whale, Peponocephala electra
- Killer whale (orca), Orcinus orca
- Pygmy killer whale, Feresa attenuata
- False killer whale, Pseudorca crassidens
- Long-finned pilot whale, Globicephala melas
- Short-finned pilot whale, Globicephala macrorhynchus
Oceanic dolphins
_NOAA.jpg)
.jpg)
_NOAA.jpg)
.jpg)
River dolphins
Hybridization
In 1933, three hybrid dolphins beached off the Irish coast; they were hybrids between Risso's and bottlenose dolphins.[16] This mating was later repeated in captivity, producing a hybrid calf. In captivity, a bottlenose and a rough-toothed dolphin produced hybrid offspring.[17] A common-bottlenose hybrid lives at SeaWorld California.[18] Other dolphin hybrids live in captivity around the world or have been reported in the wild, such as a bottlenose-Atlantic spotted hybrid.[19] The best known hybrid is the wolphin, a false killer whale-bottlenose dolphin hybrid. The wolphin is a fertile hybrid. Two wolphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose. Wolphins have also been observed in the wild.[20]
Evolution
Dolphins are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are related to the Indohyus, an extinct chevrotain-like ungulate, from which they split approximately 48 million years ago.[21][22]
The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later.[23]
Archaeoceti is a parvorder comprising ancient whales. These ancient whales are the predecessors of modern whales, stretching back to their first ancestor that spent their lives near (rarely in) the water. Likewise, the archaeocetes can be anywhere from near fully terrestrial, to semi-aquatic to fully aquatic, but what defines an archaeocete is the presence of visible legs or asymmetrical teeth.[24][25][26][27] Their features became adapted for living in the marine environment. Major anatomical changes include the hearing set-up that channeled vibrations from the jaw to the earbone which occurred with Ambulocetus 49 million years ago, a streamlining of the body and the growth of flukes on the tail which occurred around 43 million years ago with Protocetus, the migration of the nasal openings toward the top of the cranium and the modification of the forelimbs into flippers which occurred with Basilosaurus 35 million years ago, and the shrinking and eventual disappearance of the hind limbs which took place with the first odontocetes and mysticetes 34 million years ago.[28][29][30] The modern dolphin skeleton has two small, rod-shaped pelvic bones thought to be vestigial hind limbs. In October 2006, an unusual bottlenose dolphin was captured in Japan; it had small fins on each side of its genital slit, which scientists believe to be an unusually pronounced development of these vestigial hind limbs.[31]
Today, the closest living relatives of cetaceans are the hippopotamuses; these share a semi-aquatic ancestor that branched off from other artiodactyls some 60 million years ago.[32] Around 40 million years ago, a common ancestor between the two branched off into cetacea and anthracotheres; anthracotheres became extinct at the end of the Pleistocene two-and-a-half million years ago, eventually leaving only one surviving lineage: the hippo
No comments: