Je te copie-colle les réponses à ces questions données par Byron Howard sur Twitter

Why Are There Only Mammals In The City Of Zootopia?

Answer:
It made the predator/prey relationship clear. Animals that are not clearly pred/prey were avoided (like primates and some omnivores).

The movie makes sure to clarify that the city of Zootopia is a home or mammals only. It appears this was done for storytelling purposes above all else. The predator/prey relationship is key to the film’s plot and overall message, so it makes sense that anything that didn’t serve that would be skipped over. The impact of the film would not have hit as strong if there were animals outside of the predator/prey dynamic.



Are There Birds, Reptiles and Primates in the World?

Answer:

Maybe. Probably.
The least straightforward answer here may be the most interesting one on this list. We never see a single animal in the film that is not an evolved mammal. So do they exist? Obviously, once it was decided these creatures weren’t in the film, they never made a decision as to how they fit in. They probably exist, but are they evolved, or are they simply animals like the fish and insects? Will we learn this answer if we ever go back to Zootopia?

De ce que l'on a vu dans le moment, il est vrai qu'il n'y a pas d'oiseaux ni de reptiles visibles dans le film. Toutefois, cela ne veut pas dire qu'ils ne sont pas présents dans l'univers du film. Il y a des parties de Zootopia / Zootopie qui n'ont pas encore été explorées de façon détaillée à l'écran, dont la zone désertique par exemple.

J'imagine que nous en saurons plus à ce sujet, s'il y a un second opus éventuellement. Ce deuxième film mettra assurément d'autres espèces animales sous les projecteurs et toutes ne seront pas forcément des mammifères.