Okay, brevity isn't always key. X3
Dyr can be either singular or plural, as you know. But that doesn't even really matter here because it basically is a collection noun now. You're not talking about an animal or muliple animals, but animals in general. And that's the same way you treat it in English. If you say "a type of [something]", the something isn't singular or plural, technically.
Or, in short again, saying "it's a type of animals" doesn't make much sense in English. :)