The taxonomy of the killer whale, or orca, is rather complicated. Is it a whale, or is it a dolphin?
As with many topics covered on this website, I'm not an expert; but this is my attempt to make sense of this one.
Whales, dolphins and porpoises are all aquatic mammals, scientifically known as the Cetacea. You probably knew this already; but you may not have known, and may be surprised to hear, that the Cetacea belong to the order Artiodactyla, or hoofed animals, from which they are now known to have evolved.
The Cetacea are classified as either baleen whales (Mysticeti) or toothed whales (Odontoceti). The baleen whales are named after their feeding system (the baleen), which simply filters the animal's food from the water.
The Odontoceti include five superfamilies:
| • | Delphinoidea | (oceanic dolphins) |
| • | Physeteroidea | (sperm whales) |
| • | Platanistoidea | (Indian river dolphins) |
| • | Inioidea | (South American river dolphins) |
| • | Ziphioidea | (beaked whales) |
So all dolphins, strictly speaking, are also whales.
The Delphinoidea include three extant (i.e. non–extinct) families: the Delphinidae (dolphins), the Monodontidae (Arctic whales) and the Phocoenidae (porpoises). The orca (Latin name Orcinus orca) is the largest member of the Delphinidae - the dolphin family; it's the only extant species in the genus Orcinus.
Here is the (almost) full taxonomical classification of the killer whale (starting with the suborder Cetacea):
| • | Class | Mammalia | (mammals) |
| • | Order | Artiodactyla | (hoofed mammals) |
| • | Suborder | Whippomorpha | (aquatic mammals and hippopotamuses) |
| • | Infraorder | Cetacea | (aquatic mammals) |
| • | Parvorder | Odontoceti | (toothed whales) |
| • | Superfamily | Delphinoidea | (oceanic dolphins) |
| • | Family | Delphinidae | (dolphins) |
| • | Genus | Orcinus | (orcas) |
| • | Species | Orcinus orca | (killer whale, or orca) |
(It's not quite full because I've left out some clades that probably won't help anyone - including a subclass, an infraclass, a magnorder and a superorder.)
So, to return to my original question: is the killer whale (or orca) a whale or a dolphin? Well I reckon it's both. It's a dolphin, because it does indeed belong to the dolphin family; but it's also a whale, because all dolphins are whales.
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