Right, well, I can only speak from experience. The vast majority of small zoos I’ve been to have had at least one animal from every category I listed, even if say, the Artiodactyls are limited to domestic goats or the gamebirds to Indian peafowl.Maybe for large zoos, although I've been to small zoos that have lacked multiple of these categories. I think for an argument about what animals are "obligatory" for zoos, the small zoos are the most relevant ones anyways as they will inevitably have the more difficult decisions of what animals to keep or not keep given the spatial constraints.