I think “ABC” animals for both zoos and more general pop culture are largely the same. Not all of them are megafauna (though most definitely tend to be). There are plenty of people that known about and go out of their way at the zoo to see macaws, capybaras, meerkats, sloths, otters, etc. and all these are smaller species. What qualifies a species as “ABC” is how ingrained it is into larger human culture. Is it one of the first species you think of when asked What starts with this letter?That's not really what "ABC" species are in zoo jargon--they refer specifically to the charismatic megafauna that drive most casual zoogoers--elephants, giraffes, big cats, great apes, bears, rhinos, and hippos. For aquariums, add cetaceans, large sharks, and maybe pinnipeds.