A dolphin is an aquatic mammal in the clade Odontoceti (toothed whale). Dolphins belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the brackish dolphins), and possibly extinct Lipotidae (baiji or Chinese river dolphin). There are 40 extant species named as dolphins.