The largest creature ever to roam the earth, the blue whale that can measure as long as 30 meters and weigh 25 times greater than the largest elephant, is from this species. Odontocetes took a different evolutionary path. They kept their teeth and developed a highly sophisticated sensory ability called echolocation, during which pulsed sounds are produced in specialized air sinuses and focused by the melon which functions as an acoustical lens. The sounds are reflected back by the objects and received through the lower jaw, which transmits the signals to the middle ear. The signals are then analyzed in the brain to give an acoustical picture of the outside environment.
Echolocation is the same process used by doctors for ultrasound imaging.
Vision uses an enormous amount of energy, and for river dolphins, this energy is better spent on the more sophisticated echolocation. Susus, indeed, have the most evolved echolocation ability of any toothed cetacean. Most dolphins emit a single beam of echolocation clicks, which gives them a single acoustical picture of their environment. Susus emit two beams of clicks, which give them two pictures. There are the baiji of the Yangtze river system, the boto of the Amazon and Orinoco, the bhulan of the Indus, and the susu of the Ganges, Brahmaputra Megna, and Karnali river systems.