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River Dolphin
Chinese River Dolphin
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Superfamily: Platanistoidea
Families

See text

River dolphins are four living species of dolphin which reside in freshwater rivers and estuaries. 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 salt-water estuaries and near-shore marine environments. However, it is scientifically classed in the river dolphin group rather than the oceanic dolphin family.

River dolphins are in danger of extinction due to habitat loss, hunting by humans, and naturally low numbers. Also, many river dolphins possess very poor eyesight.[citation needed]

Contents

Taxonomy

The four families of river dolphins are classified by Rice, 1998[1] 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.[2][3] 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.[4][5]

Current classification by Rice (1998)

Previous classification

Extinction of the Baiji

On December 13, 2006, the Baiji (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.[4][6] The last verified sighting was in September 2004.[7] 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.[8]

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 a mammalian extinction in 50 years.

Notes

  1. ^ Rice, D. W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4. pp. 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: 11343–11347. doi:10.1073/pnas.97.21.11343. 
  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: 549–556. doi:10.1098/rspb.2000.1385. 
  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: 537–540. doi:10.1098/rsbl.2007.0292. 
  5. ^ All Headline News, Dec. 2006.
  6. ^ http://www.allheadlinenews.com/articles/7005844811
  7. ^ http://www.baiji.org/fileadmin/pdf/1206_release_YFDE.pdf
  8. ^ 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.

Simple English

River dolphins
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Superfamily: Platanistoidea
Families

See text

River dolphins are four species (types) of dolphin which live in fresh water rivers and estuaries. Three species live in fresh water rivers. The fourth species, the La Plata Dolphin, lives in salt water estuaries and the ocean.

Taxonomy

The following is the taxonomy of river dolphins, or how dolphins are classified:

How dolphins were classified by Rice (1998)

  • Superfamily Platanistoidea
    • Family Platanistidae
    • Family Iniidae
      • Amazon River Dolphin (or Boto) Inia geoffrensis
    • Family Lipotidae
    • Family Pontoporiidae
      • La Plata Dolphin (or Franciscana) Pontoporia blainvillei

How dolphins used to be classified

  • Superfamily Platanistoidea
    • Family Platanistidae
      • Ganges River Dolphin Platanista gangetica
      • Indus River Dolphin Platanista minor
    • Family Iniidae
      • Amazon River Dolphin (or Boto) Inia geoffrensis
    • Family Lipotidae
      • Chinese River Dolphin (or Baiji) Lipotes vexillifer
    • Family Pontoporiidae
      • La Plata Dolphin (or Franciscana) Pontoporia blainvillei









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