Ganges and Indus Dolphin: Platanistidae
The single member of this family is a dolphin that lives in freshwater rivers on the Indian subcontinent. At one time, scientists thought that there were two species in this family, the Indus river dolphin and the Ganges river dolphin. However, recent genetic testing shows that even though these groups are separated geographically, they are the same species. Native people call these dolphins "susu," which sounds like the noise they make when they breathe.
Ganges and Indus river dolphins are small, gray-brown dolphins. Adults measure between 5 and 8 feet (1.5 to 2.5 meters) and weigh between 150 and 200 pounds (70 to 90 kilograms). These dolphins have a long beak, or snout, and when they close their mouth, their sharp front teeth are still visible. They use these teeth to catch their prey, animals they hunt for food, mainly fish. Ganges and Indus river dolphins have a small hump behind the center of their back instead of a dorsal (back) fin. Their flippers are broad and paddle-shaped, and their blowhole is a single slit, set off-center on the top of their head. Unlike other dolphins, the opening to their ear is below their eyes.
Ganges and Indus river dolphins have poorly developed eyes. They are able to see only light and dark patterns, which is why they are sometimes called blind river dolphins. Instead of relying on sight to find food, they use a system called echolocation (eck-oh-loh-KAY-shun). Dolphins make sounds (scientists disagree about how this is done) that seem to be focused through the melon, a lump of fatty tissue in the dolphin's forehead, and skull and then sent out into the environment. When the sounds bounce back, the echo is passed through special tissue in the lower jaw to the inner ear. From the time it takes to collect the echoes, their strength, and their direction, dolphins construct a "sound picture" of their environment. This process is so sensitive, that they can "see" an object the size of a kernel of corn at a distance of 50 feet (15 meters), and can find their way around muddy waters as well as clear waters. Ganges and Indus river dolphins also use sound to communicate with each other.