Ganges river dolphin

The Ganges river dolphin (Platanista gangetica) is a species of freshwater dolphin classified in the family Platanistidae. It lives in the Ganges and related rivers of South Asia, namely in the countries of India, Nepal, and Bangladesh. It is related to the much smaller Indus river dolphin which lives in the rivers of the Indus Basin in Pakistan and northwestern India.

It is also known by the name susu (popular name) also shihu (Assamese: শিহু) in Assam and shushuk (Bengali: শুশুক) in West Bengal and Bangladesh. The Ganges river dolphin has been recognized by the Government of India as its National Aquatic Animal and is the official animal of the Indian city of Guwahati. Its first occurrence, within the Hooghly River, was documented by William Roxburgh.

The Ganges river dolphin has a rectangular, ridgelike dorsal fin and females tend to be larger than males. Ganges river dolphins usually are tan, chocolate brown, dark grey or light blue. They have an elongated, slender snout with sharp and very pointed teeth, similar to most river dolphins. The river dolphin has a rounded belly, which, combined with its rectangular dorsal fin, makes it look particularly stocky in build compared to other dolphins. Their flippers and tail flukes are large and broad. They have a large melon head used for echolocation, because they cannot see well. Their eyes are usually small due to the cloudy water. Ganges river dolphins are usually 2.2–2.6 meters long (7–8 ft). The oldest recorded animal was a 28-year-old male, 199 cm in length, although they are estimated to live up to 30 years old.

The Ganges river dolphin split from the Indus river dolphin during the Pleistocene, around 550,000 years ago. The earliest fossil identified as belonging to the species is only 12,000 years old.

The Ganges river dolphin was formally classified as Delphinus gangeticus two separate times in 1801, by Heinrich Julius Lebeck and William Roxburgh. They both likely used the type specimen, caught near Calcutta in late 1797 and sent to the Hunterian Museum in London. It may have been destroyed during World War II, but castings were previously made of the rostrum and parts of the lower jaw, which survive at the Natural History Museum. Whether Lebeck or Roxburgh should be given credit has been debated over the centuries, but research by Kinze (2000) found that Lebeck's description was published on the 24 August while Roxburgh's was likely published no earlier than September, thus giving Lebeck the priority. Elisha Gray coined the species name Platanista gangetica in 1835.

This species and the Indus river dolphin, were initially classified as a single species, Platanista gangetica, but in the 1970s both were split into distinct species. However, in the 1990s, both species were again grouped as a single species. However, more recent studies of genes, divergence time, and skull structure support both being distinct species.

The species has multiple common names throughout its range. It is known as susu as a popular name, soons, soans, or soos in Hindi, shushuk in Bengali, hiho or hihu in Assamese, bhagirath (as a reference to the character of the same name from Hindu mythology), and shus or suongsu in Nepali. Its Sanskrit name in medieval times was likely shishumar, and during the Mughal era, it was known as pani suar.

It lives along the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Bangladesh and India, and the Sapta Koshi and Karnali Rivers in Nepal. The Ganges river dolphin favours deep pools, eddy countercurrents located downstream of the convergence of rivers and of sharp meanders, and upstream and downstream of midchannel islands.