Featured Article Summary #24

The South Asian river dolphins are toothed whales that live in freshwater habitats in the northern Indian subcontinent. They were previously considered one species but are now recognized as separate species, the Ganges river dolphin and the Indus river dolphin. These dolphins have distinct genetic and morphological differences and are estimated to have diverged 550,000 years ago. They are the only members of their family and superfamily. These dolphins have small eyes and rely on echolocation to navigate in murky waters. They have large crests on their skulls that help with echolocation. They feed on fish and shrimp and are active during the day in small groups. Both species are endangered due to various threats such as dams, fishing nets, and pollution. Originally thought to be one species with two subspecies, South Asian river dolphins in the Ganges and Indus Rivers were later considered to be separate species due to differences in physical characteristics and genetic studies. However, a recent study in 2021 confirmed that they are indeed distinct species based on significant genetic divergence and noticeable differences in skull structure. South Asian river dolphins are distinct from other river dolphins, as they are not closely related to them and have independently adapted to freshwater habitats. Fossil evidence shows that the lineage of South Asian river dolphins dates back millions of years, and they likely migrated to their current habitat through stream capture in the last five million years. The two separate species of South Asian river dolphins diverged around 550,000 years ago. South Asian river dolphins have a unique appearance with stocky bodies, broad pectoral fins, and slender snouts. They have primitive features, such as a cecum and air sacs near the blowhole. The dolphins vary in size and weight between the Ganges and Indus species, with the Indus dolphins tending to be heavier. They have special adaptations for their environment, including unusual skull features, curved teeth, and adaptations for vision and hearing in murky waters. South Asian river dolphins live in rivers and waterways in the northern part of the Indian subcontinent, including the Ganges, Brahmaputra, Meghna, Karnaphuli, and Sangu rivers. They can be found in Nepal, India, and Bangladesh, and possibly Bhutan. The dolphins prefer areas with stable water levels, such as stream pools, meanders, confluences, and river islands. They usually stay in shallower water, but can be found in deeper pools occasionally.