Delphinids: Killer Whales

Orca / killer whale

The dolphin family is scientifically defined as including all the species more closely related to the common dolphin than they are to porpoises. The great majority are what we'd normally think of as "dolphins" but four species are so much larger that, instead, we tend to call them "whales". Three, including the two species of pilot whale, are of roughly similar size to each other, but the fourth is noticeably larger still.

It's the biggest "dolphin" of all: the orca or killer whale (Orcinus orca).

That it is a dolphin has never been seriously doubted from a scientific perspective. It is one of just three species of dolphin to be listed as such in the first catalogue of scientific names in 1758 - and one of the other two is a porpoise, and so has since been moved elsewhere. On the other hand, it has been recognised as belonging to a distinct subfamily with the dolphins since 1846, and modern genetic studies confirm that its ancestors diverged from those of most other dolphins unusually early.