Talk:Zootopia/@comment-4087607-20151025223048/@comment-4352233-20151026001428

Because they wanted to show that the relationship between Nick & Judy is one that is based on that of predator and prey (they will have trouble working together), and this interaction between species is most common in mammals, which can be either herbivores or carnivores. Most birds, reptiles, amphibians and fishes eat other animals, so it would be confusing to use them. But I'm pretty sure that these other vertebrate classes have cities of their own in this world.