River or Freshwater Dolphins
Five Dolphins That Don't Live in the Open Ocean
Five species of dolphin have evolved to live in big, muddy rivers. Convergent evolution has made them look very similar despite little genetic connection.
Dolphins live in the ocean right?
Actually there are five species known as river or freshwater dolphins. One may be extinct in the wild and one spends most of its time along the coast but all five dolphins share a preference for big, murky rivers. They no longer require a salt water environment, as most dolphins do.
Although these dolphins look very similar it is likely that this is a result of convergent evolution. In other words, because of similar habitat use and feeding strategy they developed similar features. Other than the Indus and Ganges River dolphin they are very different genetically.
Living in rivers their eyes have become tiny (there’s not much to see in the muddy waters and, they use sonar to find fish) and their beaks have become long, possibly for rooting around in the muddy river bottoms.
WHO ARE THEY?
In South America there are two:
The Boto or Amazon River Dolphin (Inia geoffrensis) who inhabits the Amazon and Orinoco River Basins and the upper Madeira River. These are the largest of the river dolphins and they are known for their pink color.
The Franciscana or La Plata River Dolphin (Pontoporia blainvillei). This is the one who prefers shallow coastal areas such as the LaPlata Estuary. It is found from the Doce River in Brazil to Peninsula Valdez in Argentina. It is the smallest of the river dolphins with the longest beak and a grayish-brown back and pale belly.
In Asia there are three:
The Baiji or Yangtze River Dolphin may already be extinct in the wild. But because it is shy and very difficult to see there is an outside chance a few might be left. The Yangtze River in China is the only place where this bluish grey species existed
The Ganges River Dolphin or Susu (Platanista gangetica), is found in the Ganges, Brahmaputra and Meghna rivers in India, Nepal, Bhutan and Bangladesh. Three color variations are found-greyish blue, pale blue and chocolate brown.
The Indus River Dolphin (Platanista minor) is found in the Indus River in Pakistan, mostly in the Sind and Punjab provinces. It is uniformly grey brown. Once considered a subspecies of the Ganges River Dolphin, it is now a species in its own right.
