think about it

Simple. Birds and fish! I looked it up, it's canon.

Thank you you for telling me this. But Birds and Fish are animals too. You can find them in a zoo too. Zootopia is now racist.

Not necessarily. The mammals are evolved, but not insects, birds, and fish. Plus, it's better than going after each other.

hmmmmmm or reptiles! I just realized there were no reptiles! but why didn't the birds, incest, fish fish not evolve? Evolution is stated to be a naturally occurring process, it doesn't just stop.

It probably has something to do with things only mammals have. Reptiles birds and fish might not have the same potential. Don’t forget humans are mammals to. It’s highly possible that the requirements for intelligent brains to start developing is only present in mammals.