I'm planning a map in the XL map in Zoo Tycoon 2 ans I was wondering about zoos that have the ABC species and is 60 acres or under.
Take a look at Houston Zoo. They have 55 acres and one of the best collections in the country. Only major species lacking is hippo, and that's in the design stage right now.
Schönbrunn (Vienna) is 17 ha/42 acres and a top zoo regardless of size. In fact, I do consider it the single best zoo for families with smaller children since the only I personally rate higher (2x Berlin, Bronx, San Diego, etc) all are quite large, hilly and/or just too rich in species. Children and most ordinary zoo visitors get tired before seeing half. Schönbrunn is manageable in size, doesn't have any bad exhibits (some are average, but nothing below) and has pretty much all the ABC species, incl. less regular ones like giant panda and koala. From a design perspective parts of Schönbrunn are unusual because of the relatively high number of protected buildings, but they've generally solved this quite excellently.
Basel is even smaller than Schoenbrun, but has all the ABC's except tigers, most of them in good exhibits.