It turns out that the term "whale" describes two very different groups of cetaceans: 1. The Odontoceti, or toothed whales, which comprise the sperm whale, belugas, narwhals, orcas, dolphins and porpoises. 2. read more
Thus, the term 'whale' is not that important, because basically it means a medium to large size cetacean. Incidentally, beluga whales and narwhals are closely related and are the only members of the family Monodontidae (Monodontidae). read more
(2) Toothed whales (otherwise known as odontocetes and including all species of dolphin and porpoise) – which as you would expect, have teeth, and eat larger prey items, including at times, other marine mammals. read more
The beluga is a whale because it is quite large but is most closely related to a species called the Irrawady dolphin, which looks more like a porpoise! Figure that one out if you can! Belugas are more closely related to dolphins and porpoises than to baleen whales or the big toothed whales (like the sperm whale). read more