Well, consider ligers or zebra-horses. Or mules.
Sometimes animals can make babies, even with different numbers of chromosomes. The offspring is just sterile.
If everything in the zootopia world is sharing enough DNA to think human, talk human, and walk upright like a human.
Plus, another fun thing to think about? The placenta and live birth system is due to a virus. All mammals save two species are in symbiosis with an ancient virus that allows the whole placenta thing to happen.
If I was to write a sci-fi version of zootopia, I'd target that as a starting point. A forced evolutionary virus that has a strong stake in helping things reproduce to reproduce itself. If a random mutation caused such a thing to allow crossbreeding, it would instantly become a more successful virus.
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