The orca, or killer whale, is the dolphin species with the tallest dorsal fin. Despite its common name, the orca is the largest member of the oceanic dolphin family, Delphinidae.
The dorsal fin is especially striking in adult males, where it can rise roughly 1.8 metres above the back. It is tall, triangular, and relatively rigid. Females and juveniles have shorter, more curved fins. The fin helps stabilize the animal while swimming, much as a keel stabilizes a boat, but it is not used to produce the main thrust; that comes from the tail flukes.
Orcas are often confused with dolphins because their massive bodies, black-and-white markings, and powerful hunting style make them look unlike familiar small dolphins. However, their anatomy, social behaviour, and evolutionary relationships place them firmly among the dolphins.
The dorsal fin is also useful for recognising individuals in the wild. Researchers photograph distinctive nicks, scars, and shapes to identify animals and track family groups over many years. Other dolphins have prominent fins, but none matches the height of a mature male orca’s.