Which dolphin is the largest species of dolphin?

The largest species of dolphin is the orca, also called the killer whale.

Orcas belong to the family Delphinidae, the oceanic dolphins, even though their common name includes the word “whale.” Their scientific name is Orcinus orca. This makes the orca a useful reminder that everyday names do not always match biological classification: taxonomically, it is a dolphin and also a toothed whale, because dolphins are nested within the toothed-whale group.

Orcas are powerful, highly social predators found in oceans worldwide. They often live in stable family groups called pods, and different populations may specialize in hunting fish, seals, rays, sharks, dolphins, or other whales. Their black-and-white coloring and tall dorsal fin make them particularly recognizable.

The common dolphin and bottlenose dolphin are true members of Delphinidae, but they are far smaller. Risso's dolphin is also in that family, yet none approaches the orca's size. “Killer whale” does not mean the animal is a fish or a separate non-dolphin category; it is the traditional common name for the world's largest dolphin.