But they are not in the dolphin family. They are in the Monodontidae family. The other lonely member of this family is the Beluga whale. Monodontidae are white whales with blunt heads and no dorsal fin. That big spike coming out the whale's forehead is really its left upper tooth.
Narwhals live in the arctic and are said to be rare.
Pretty soon we will be separating out all the other cetacean families, insisting they are also not whales, and then there won't be anything left to call a whale. I'm kidding, of course, but the point is that names like dolphin and whale can be pretty arbitrary and illogical. That's why we need the taxonomists to give us words like cetacean and delphinidae that are clearly defined. The killer whale above is chasing a seal. Seals are not cetaceans.