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==Taxonomy==
==Taxonomy==
The four [[family (biology)|families]] of river dolphins are classified by Rice, 1998<ref name="Rice" /> 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.<ref name=Cassens2000>{{cite journal | author = Cassens, I., S. Vicario, V. G. Waddell, H. Balchowsky, D. Van Belle, W. Ding, C. Fan, R. S. L. Mohan, P. C. Simoes-Lopes, R. Bastida, A. Meyer, M. J. Stanhope, and M. C. Milinkovitch | year = 2000 | title = Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 97 | pages = 11343–11347 | doi = 10.1073/pnas.97.21.11343 | pmid = 11027333 | issue = 21 | pmc = 17202}}</ref><ref name=Hamilton2001>{{cite journal | author = Hamilton, H., S. Caballero, A. G. Collins, and R. L. Brownell Jr. | year = 2001 | title = Evolution of river dolphins | journal = Proceedings of the Royal Society of London Series B: Biological Sciences | volume = 268 | pages = 549–556 | doi = 10.1098/rspb.2000.1385 | pmid = 11296868 | issue = 1466 | pmc = 1088639}}</ref> 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]].<ref name=Turvey2007>{{cite journal | author = Turvey, S. T., R. L. Pitman, B. L. Taylor, J. Barlow, T. Akamatsu, L. A. Barrett, X. Zhao, R. R. Reeves, B. S. Stewart, K. Wang, Z. Wei, X. Zhang, L. T. Pusser, M. Richlen, J. R. Brandon and D. Wang | year = 2007 | title = First human-caused extinction of a cetacean species? | journal = Journal of the Royal Society, Biology Letters | volume = 3 | pages = 537–540 | doi = 10.1098/rsbl.2007.0292 | pmid = 17686754 | issue = 5 | pmc = 2391192}}</ref><ref>[http://www.allheadlinenews.com/articles/7005844811 All Headline News], Dec. 2006.</ref>
The four [[family (biology)|families]] of river dolphins are classified by Rice, 1998<ref name="Rice" /> as belonging to the superfamily [[Platanistoidea]]. Formerly, [[Platanistoidea]] 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.<ref name=Cassens2000>{{cite journal | author = Cassens, I., S. Vicario, V. G. Waddell, H. Balchowsky, D. Van Belle, W. Ding, C. Fan, R. S. L. Mohan, P. C. Simoes-Lopes, R. Bastida, A. Meyer, M. J. Stanhope, and M. C. Milinkovitch | year = 2000 | title = Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 97 | pages = 11343–11347 | doi = 10.1073/pnas.97.21.11343 | pmid = 11027333 | issue = 21 | pmc = 17202}}</ref><ref name=Hamilton2001>{{cite journal | author = Hamilton, H., S. Caballero, A. G. Collins, and R. L. Brownell Jr. | year = 2001 | title = Evolution of river dolphins | journal = Proceedings of the Royal Society of London Series B: Biological Sciences | volume = 268 | pages = 549–556 | doi = 10.1098/rspb.2000.1385 | pmid = 11296868 | issue = 1466 | pmc = 1088639}}</ref> Many of the morphological similarities and adaptations to freshwater habitats arose due to [[convergent evolution]], thus the superfamily [[Platanistoidea]] is [[paraphyly|paraphyletic]]. A December 2006 survey found no members of ''[[Lipotidae]]'' (commonly known as the [[Yangtze River]] dolphin) and declared the species functionally [[extinct]].<ref name=Turvey2007>{{cite journal | author = Turvey, S. T., R. L. Pitman, B. L. Taylor, J. Barlow, T. Akamatsu, L. A. Barrett, X. Zhao, R. R. Reeves, B. S. Stewart, K. Wang, Z. Wei, X. Zhang, L. T. Pusser, M. Richlen, J. R. Brandon and D. Wang | year = 2007 | title = First human-caused extinction of a cetacean species? | journal = Journal of the Royal Society, Biology Letters | volume = 3 | pages = 537–540 | doi = 10.1098/rsbl.2007.0292 | pmid = 17686754 | issue = 5 | pmc = 2391192}}</ref><ref>[http://www.allheadlinenews.com/articles/7005844811 All Headline News], Dec. 2006.</ref>


The current classification of river dolphins (Rice, 1998) is as follows:
The current classification of river dolphins (Rice, 1998) is as follows:
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***Genus †''[[Lipotes]]''
***Genus †''[[Lipotes]]''
****''[[Baiji]]'' (or Chinese river dolphin), †''Lipotes vexillifer'' (functionally extinct, since December 2006)
****''[[Baiji]]'' (or Chinese river dolphin), †''Lipotes vexillifer'' (functionally extinct, since December 2006)

In 2012 the [[Society for Marine Mammalogy]]<ref name="MMS">"[http://www.marinemammalscience.org/index.php?option=com_content&view=article&id=645&Itemid=340]" Committee on Taxonomy. 2012. List of marine mammal species and subspecies. Society for Marine Mammalogy, www.marinemammalscience.org, consulted on May, 6 2012. </ref> began considering the Bolivian (''Inia geoffrensis boliviensis'') and Amazonian (''Inia geoffrensis geoffrensis'') subspecies as full species ''Inia boliviensis'' and ''Inia geoffrensis'', respectively; however, much of the scientific community, including the [[IUCN]],<ref name="iucn">{{cite book |author=R.R. Reeves, T.A. Jefferson, L. Karczmarski, K. Laidre, G. O'Corry-Crowe, L. Rojas-Bracho, E.R. Secchi, E. Slooten, B.D. Smith, J.Y. Wang, & K. Zhou|title =IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. |chapter=''Inia geoffrensis''|publisher =International Union for Conservation of Nature and Natural Resources|year =2011|url =http://www.iucnredlist.org/apps/redlist/details/10831/0}}</ref> consider the ''boliviensis'' population to be a subspecies of ''Inia geoffrensis''.


==Differences between marine and river dolphins==
==Differences between marine and river dolphins==

Revision as of 14:54, 6 May 2012

River dolphins
Baiji (Lipotes vexillifer)
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Cetacea
Suborder:
Odontoceti
Superfamily:
Platanistoidea
Families

See text

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 cetaceans. Three species live in fresh water rivers. The fourth species, the La Plata dolphin, lives in saltwater estuaries and near-shore marine environments. However, it is scientifically classed in the river dolphin group rather than the oceanic dolphin 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.[1]

Taxonomy

The four families of river dolphins are classified by Rice, 1998[1] as belonging to the superfamily Platanistoidea. Formerly, Platanistoidea 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.[2][3] Many of the morphological similarities and adaptations to freshwater habitats arose due to convergent evolution, thus the superfamily Platanistoidea is paraphyletic. A December 2006 survey found no members of Lipotidae (commonly known as the Yangtze River dolphin) and declared the species functionally extinct.[4][5]

The current classification of river dolphins (Rice, 1998) is as follows:

File:Delfinrosado.jpg
Pink Amazon river dolphin, Inia geoffrensis
  • Superfamily †Lipotoidea
    • Family †Lipotidae
      • Genus †Lipotes
        • Baiji (or Chinese river dolphin), †Lipotes vexillifer (functionally extinct, since December 2006)

In 2012 the Society for Marine Mammalogy[6] began considering the Bolivian (Inia geoffrensis boliviensis) and Amazonian (Inia geoffrensis geoffrensis) subspecies as full species Inia boliviensis and Inia geoffrensis, respectively; however, much of the scientific community, including the IUCN,[7] consider the boliviensis population to be a subspecies of Inia geoffrensis.

Differences between marine and river dolphins

Both river dolphins and marine dolphins belong to a group of mammals called cetaceans, but they differ somewhat in appearance. For example, the snout of a river dolphin measures about 58 centimeters (2 ft) 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 fish.[1]

Extinction of the baiji

On December 13, 2006, the baiji (Lipotes vexillifer) was declared "functionally extinct", after a 45-day search by leading experts in the field failed to find a single specimen.[4][8] The last verified sighting was in September 2004.[9] 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.[10]

Overfishing, damming and subaquatic sonar pollution (which interfered with the dolphins' sonar-based method of locating food), is believed to have led to their extinction. Reuters news reported this as 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 978-0-00-714178-4, is much about the river dolphin in Bangladesh.

Non-river dolphins in riverine environments

Some oceanic dolphins live in fluvial environments, but are not classified as river dolphins. The river dolphins should also not be confused with freshwater populations of porpoises.

Of the oceanic dolphins found in freshwater or brackish environments, include the Irrawaddy dolphin.

Of the porpoises found in freshwater or brackish environments, include the Finless porpoise.

Notes

  1. ^ a b c Rice, D. W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4. p. 231.
  2. ^ Cassens, I., S. Vicario, V. G. Waddell, H. Balchowsky, D. Van Belle, W. Ding, C. Fan, R. S. L. Mohan, P. C. Simoes-Lopes, R. Bastida, A. Meyer, M. J. Stanhope, and M. C. Milinkovitch (2000). "Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages". Proceedings of the National Academy of Sciences of the United States of America. 97 (21): 11343–11347. doi:10.1073/pnas.97.21.11343. PMC 17202. PMID 11027333.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ Hamilton, H., S. Caballero, A. G. Collins, and R. L. Brownell Jr. (2001). "Evolution of river dolphins". Proceedings of the Royal Society of London Series B: Biological Sciences. 268 (1466): 549–556. doi:10.1098/rspb.2000.1385. PMC 1088639. PMID 11296868.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ a b Turvey, S. T., R. L. Pitman, B. L. Taylor, J. Barlow, T. Akamatsu, L. A. Barrett, X. Zhao, R. R. Reeves, B. S. Stewart, K. Wang, Z. Wei, X. Zhang, L. T. Pusser, M. Richlen, J. R. Brandon and D. Wang (2007). "First human-caused extinction of a cetacean species?". Journal of the Royal Society, Biology Letters. 3 (5): 537–540. doi:10.1098/rsbl.2007.0292. PMC 2391192. PMID 17686754.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ All Headline News, Dec. 2006.
  6. ^ "[1]" Committee on Taxonomy. 2012. List of marine mammal species and subspecies. Society for Marine Mammalogy, www.marinemammalscience.org, consulted on May, 6 2012.
  7. ^ R.R. Reeves, T.A. Jefferson, L. Karczmarski, K. Laidre, G. O'Corry-Crowe, L. Rojas-Bracho, E.R. Secchi, E. Slooten, B.D. Smith, J.Y. Wang, & K. Zhou (2011). "Inia geoffrensis". IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature and Natural Resources.{{cite book}}: CS1 maint: multiple names: authors list (link)
  8. ^ http://www.allheadlinenews.com/articles/7005844811
  9. ^ http://www.baiji.org/fileadmin/pdf/1206_release_YFDE.pdf
  10. ^ http://www.usatoday.com/tech/science/2007-08-29-china-dolphin_N.htm

References

  • Reeves, Randall R. et al. (2002). National Audubon Society guide to marine mammals of the world. Alfred A. Knopf. 527 pp.
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