River dolphin
Encyclopedia
River dolphins are the four living species of dolphin
that reside in freshwater rivers and estuaries. River dolphins inhabit areas of Asia and South America. They are classed in the Platanistoidea superfamily of cetacea
ns. Three species live in fresh water
rivers. The fourth species, the La Plata Dolphin
, lives in salt-water estuaries
and near-shore marine environments. However, it is scientifically classed in the river dolphin group rather than the oceanic dolphin
family.
The amazon river dolphin is the largest freshwater dolphin in the world.
of river dolphins are classified by Rice, 1998 as belonging to Platanistoidea. Formerly Platanistidae was listed as the only extant family of the Platanistoidea superfamily. The previously accepted classification treated all four families as belonging to this family and treated the Ganges and Indus River Dolphins as separate species. Five lineages of dolphin have evolved to live in big, muddy rivers. River dolphins are thought to have relictual distributions. Their ancestors originally occupied marine habitats, but were then displaced from these habitats by modern dolphin lineages. Many of the morphological similarities and adaptations to freshwater habitats arose due to convergent evolution
. A December 2006 survey found no members of Lipotidae (commonly known as the Yangtze River
dolphin) and declared the species functionally extinct.
.
(aka Yangtze River Dolphin and Chinese River Dolphin) was declared "functionally extinct", after a 45-day search by leading experts in the field failed to find a single specimen. The last verified sighting was in September 2004. In August 2007, reports surfaced that a man saw and videotaped what appears to be a Baiji in the Yangtze River. A team of scientists attempted to verify the sighting beginning in September 2007.
It is believed that overfishing, damming and sub-aquatic sonar pollution (which interfered with the dolphin's sonar-based method of locating food), led to the extinction. Reuters news reported this their first record of an aquatic mammalian extinction in 50 years.
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
that reside in freshwater rivers and estuaries. River dolphins inhabit areas of Asia and South America. They are classed in the Platanistoidea superfamily of cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
ns. Three species live in fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
rivers. The fourth species, the La Plata Dolphin
La Plata Dolphin
The La Plata Dolphin or Franciscana 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...
, lives in salt-water estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
and near-shore marine environments. However, it is scientifically classed in the river dolphin group rather than the oceanic dolphin
Oceanic dolphin
Oceanic dolphins are the members of the Delphinidae family of cetaceans. These marine mammals are related to whales and porpoises. They are found worldwide, mostly in the shallower seas of the continental shelves...
family.
Characteristics
The largest river dolphins usually grow up to 2.4 meters (8 feet) long, but most of the animals are smaller. River dolphins may be white, pink, yellow, brown, gray, or black.The amazon river dolphin is the largest freshwater dolphin in the world.
Taxonomy
The four familiesFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of river dolphins are classified by Rice, 1998 as belonging to Platanistoidea. Formerly Platanistidae was listed as the only extant family of the Platanistoidea superfamily. The previously accepted classification treated all four families as belonging to this family and treated the Ganges and Indus River Dolphins as separate species. Five lineages of dolphin have evolved to live in big, muddy rivers. River dolphins are thought to have relictual distributions. Their ancestors originally occupied marine habitats, but were then displaced from these habitats by modern dolphin lineages. Many of the morphological similarities and adaptations to freshwater habitats arose due to convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
. A December 2006 survey found no members of Lipotidae (commonly known as the Yangtze River
Yangtze River
The Yangtze, Yangzi or Cháng Jiāng is the longest river in Asia, and the third-longest in the world. It flows for from the glaciers on the Tibetan Plateau in Qinghai eastward across southwest, central and eastern China before emptying into the East China Sea at Shanghai. It is also one of the...
dolphin) and declared the species functionally extinct.
Current classification by Race (1998)
- Superfamily Platanistoidea
- Family Platanistidae
- Genus Platanista
- Ganges and Indus River Dolphin, Platanista gangetica with two subspecies
- Ganges River Dolphin (or Susu), Platanista gangetica gangetica
- Indus River DolphinIndus River dolphinThe Indus River dolphin is a sub-species of freshwater or river dolphin found in the Indus River of Pakistan...
(or Bhulan), Platanista gangetica minor
- Ganges and Indus River Dolphin, Platanista gangetica with two subspecies
- Genus Platanista
- Family Platanistidae
- Superfamily Inioidea
- Family IniidaeIniidaeIniidae is a family of river dolphins containing one living and three extinct genera.-Taxonomy:The family was described by John Edward Gray in 1846.Current classifications include a single living genera, Inia, with one species and three subspecies...
- Genus IniaIniaInia is a genus of river dolphin containing one or possibly two species.-Taxonomy:The genus was described by Alcide d'Orbigny in 1834 when Delphinus geoffrensis, described by Henri Marie Ducrotay de Blainville in 1817, was recognized to be a unique taxon...
- Amazon River Dolphin (or Boto), Inia geoffrensis
- Inia geoffrensis geoffrensis
- Inia geoffrensis boliviensis
- Inia geoffrensis humbotiana
- Amazon River Dolphin (or Boto), Inia geoffrensis
- Genus Inia
- Family Pontoporiidae
- Genus PontoporiaPontoporiaPontoporia may refers to:* The La Plata Dolphin, re: film PONTOPORIA, EL DELFIN DEL PLATA, 30 min. B&W. sound. Camera, editing, director: Eduardo Darino, for ICUR,Instituto de Cine, Universidad de la Republica, Uruguay....
- La Plata DolphinLa Plata DolphinThe La Plata Dolphin or Franciscana 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...
(or Franciscana), Pontoporia blainvillei
- La Plata Dolphin
- Genus Pontoporia
- Family Iniidae
- Superfamily †Lipotoidea
- Family †Lipotidae
- Genus †Lipotes
- BaijiBaijiBaiji may refer to:* The Baiji or Yangtze River Dolphin * Baiji, Iraq, a city of northern Iraq.* "Baiji" is the pinyin Romanization for Baekje....
(or Chinese River Dolphin), †Lipotes vexillifer (functionally extinct, since December 2006)
- Baiji
- Genus †Lipotes
- Family †Lipotidae
Previous classification
- Family Platanistidae
- Ganges River Dolphin (or Susu), Platanista gangetica
- Indus River DolphinIndus River dolphinThe Indus River dolphin is a sub-species of freshwater or river dolphin found in the Indus River of Pakistan...
(or Bhulan), Platanista minor - Amazon River Dolphin (or Boto), Inia geoffrensis
- Chinese River Dolphin (or Baiji), Lipotes vexillifer (presumed extinct as of 2006)
- La Plata DolphinLa Plata DolphinThe La Plata Dolphin or Franciscana 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...
(or Franciscana), Pontoporia blainvillei
Difference Between Marine and River Dolphins
Both river dolphins and marine dolphins belong to a group of mammals called cetaceans. But these two dolphins differ somewhat in appearance. For example, the snout of a river dolphin measures about 58 centimeters [2 foot] long, approximately four times as long as that of most marine dolphins. River dolphins have smaller eyes than marine dolphins, and their vision is poorly developed because they live in dark, muddy water. This environment also makes river dolphins less active than marine dolphins. River dolphins feed primarily on fishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
.
Extinction of the Baiji
On December 13, 2006, the BaijiBaiji
Baiji may refer to:* The Baiji or Yangtze River Dolphin * Baiji, Iraq, a city of northern Iraq.* "Baiji" is the pinyin Romanization for Baekje....
(aka Yangtze River Dolphin and Chinese River Dolphin) was declared "functionally extinct", after a 45-day search by leading experts in the field failed to find a single specimen. The last verified sighting was in September 2004. In August 2007, reports surfaced that a man saw and videotaped what appears to be a Baiji in the Yangtze River. A team of scientists attempted to verify the sighting beginning in September 2007.
It is believed that overfishing, damming and sub-aquatic sonar pollution (which interfered with the dolphin's sonar-based method of locating food), led to the extinction. Reuters news reported this their first record of an aquatic mammalian extinction in 50 years.
In Literature
- The Hungry Tide, by Amitav Ghosh - novel, HarperCollins; New Ed edition (3 May 2005), ISBN 9780007141784, is much about the river dolphin in Bangladesh.