platanista

“External similarities among the three extant river dolphins and Pontoporia. The painting shows shared characteristics including long and narrow rostrum, small eyes, and broad forelimb flippers. A poorly-developed dorsal fin characterizes Inia (top), Platanista (second from top), and Lipotes (second from bottom) but is absent in the coastal Pontoporia (bottom). Note that the painting is for comparative purposes only; the geographic ranges of these species are disjunct”

A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea. Jonathan H Geisler, Michael R McGowen, Guang Yang and John Gatesy. BMC Evolutionary Biology 2011, 11:112 doi:10.1186/1471-2148-11-112

INDIA’S FIRST RESERVE FOR GANGES RIVER DOLPHINS SOON IN WEST BENGAL

To protect the endangered Ganges river dolphins, West Bengal will soon have the country’s first community reserve for this cetacean.

Declared in 2012 as National Aquatic Animal of India, tjeir number is estimated to be less than 2,000.  Direct killing, habitat fragmentation due to construction of dams and barrages, indiscriminate fishing and pollution of rivers are some of the major threats affecting the species.

The Ganga stretch in West Bengal, also known as Hooghly, is about 500 km long and passes though Kolkata before meeting the Bay of Bengal in the Sundarbans. According to Chief Wildlife Warden, and Principal Chief Conservator of Forest (Wildlife), Azam Zaidi, this stretch is not within a forest or a sanctuary, and thus it is important to protect the dolphins in the region. The reserve will be set up in the Hooghly River, between the Malda and South 24 Paraganas districts. The final decision for the reserve was taken at a meeting of the State Wildlife Board.

The Ganges River dolphin, or susu inhabits the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Nepal, India, and Bangladesh.Once found in thousands, there are fewer than 2,000 left in the country in the entire distribution range along the Ganga and Brahamaputra river system.

PLASTINOIDS DOLPHINS

John D Orcutt UO

Modern dolphins are by many measures the most successful group of cetaceans: they are diverse, intelligent, and in many cases have proven more resistant to anthropogenic change than their larger relatives. Some dolphins have even colonized freshwater environments. These ‘river dolphins’ are often referred to as platanistoids, a name based on the modern genus Platanista that inhabits the Ganges and Indus Rivers (other generus inhabit the AmazonLa Plata, and - until recently - Yangtze Rivers), but there has been much debate about whether or not all river dolphins are actually related, as was originally thought. If the world’s living and extinct river dolphins really are the product of separate colonizations of freshwater habitats, then they represent a striking example of convergent evolution: platanistoids share many morphological characteristics, perhaps the most striking being a long, pointed rostrum (or snout; this feature makes them similar in form to many other fish-eating vertebrates, such as ichthyosaurs and swordfish).

The specimen at left, an as-yet unnamed platanistoid from the mid-Miocene of Oregon, exhibits this characteristic rostrum. However, it was uncovered from the Astoria Formation, a marine unit from the Oregon Coast, making it a saltwater freshwater dolphin. This implies that at least one lineage of river dolphins evolved its unusual morphology before migrating inland. 

A dalpiazinid dolphin, based on this undescribed skull. These obscure fossil cetaceans are known from the Oligocene and Miocene epochs (~26-15 mya) of Italy and New Zealand. Related to the river dolphins, their closest living relative is the South Asian river dolphin (Platanista gangetica).

They had particularly long forward-pointing tusk-like teeth at the tip of the upper jaw, the function of which is unknown.

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Gangetic Dolphins (Platanista gangetica gangetica) of India

The Ganges River Dolphins are one of a kind of fresh water dolphin species facing the risk of extinction. These beautiful creatures were once abundant in the Ganges, Brahmaputra, Meghna, Karnaphuli and Sangu river systems of Nepal, Bangladesh and India. They usually travel alone or in very small groups. They are different from their salt water cousins, as unlike them they move in a slow, leisurely manner through deep water, and prefer to remain close to the river bed.

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