poothos asked: i've always heard that killer whales are actually dolphins - but is this a misnomer? are dolphins actually whales??
Well, first off, killer whales are part of the family Delphinidae, which includes all oceanic dolphins. Here’s a phylogeny (note that it is split up into the Globicephalinae and Delphininae subfamilies- be careful not to get Delphininae mixed up with Delphinidae. Thanks, science.)
(Figure taken from this paper.)
So by that logic, you’d say “Yes, killer whales are dolphins.” But then of course we run into a problem, because a whole separate group of marine mammals are called dolphins- the river dolphins (superfamily Platanistoidea).
Like this cute lil Baiji.
And of course both Delphinidae and Platanistoidea fall under the suborder Odontoceti, the toothed whales, so there all of the sudden is your whale.
(Taken from this page.)
And this group includes things like the sperm whale, so it’s not like everything in Odontoceti is a dolphin- you wouldn’t call this handsome fellow a dolphin.
The Odontoceti have a sister suborder called the Mysticeti, the baleen whales, and that includes your humpback et cetera. They’re all together in the order Cetacea.
So if you’d consider everything in Cetacea a whale, then yes, dolphins are whales, and killer whales are dolphins if you consider everything in Delphinidae a dolphin. But the point is that the common names can refer to a bunch of different things that generally aren’t monophyletic- try narrowing down the common definition for ‘porpoise,’ which lots of people use to refer to dolphins, but which actually refers to a group of small cetaceans within Odontoceti (family Phocoenidae).
Basically, common names can be iffy; when in doubt look at the biological name and the phylogeny.