What is the smallest dolphin species?

There is not really one smallest species. The smallest species include: True dolphins (Delphinidae): * Tucuxi (Sotalia fluviatilis) – 1.3 to 1.8 m * Hector’s dolphin (Cephalorhynchus hectori) – 1.2 to 1.5 m * Black dolphin (Cephalorhynchus eutropia) – 1.2 to 1.7 m * Commerson’s dolphin (Cephalorhynchus commersonii) – 1.3 to 1.7 m River dolphins (Platanistidae): * Franciscana (Pontoporia blainvillei) – 1.3 to 1.7 m Porpoises (Phocoenidae): * Vaquita (Phocoena sinus) – 1.2 to 1.5 m * Finless porpoise (Neophocaena phocaenoides) – 1.2 to 1.9 m