Plot hole: The newspaper headline showing young Alex being rescued from a crate is dated April 8, 1972. In the next scene, we see young Alex dancing in the Central Park Zoo, and watching him are Marty, Melman and Gloria as baby animals. This makes no sense at all. In the first film, Marty celebrates his tenth birthday. Key word: tenth. It is also known that the scenes of the main characters as adults take place in the present i.e. Alex confessing to breaking Marty's iPod. Seeing how the animals age quicker than humans, Marty, let alone his three friends, would have to have been born in the mid-1990s and the flashback scenes could not have taken place in 1972.
Continuity mistake: At the end of the movie, it's revealed how Alex can tell Marty apart from all of the other Zebras - when Marty walks away from the "camera" it shows the huge bite mark on his backside that Alex gave him in the first movie. However, the bite mark is never seen in any other shots of Marty's backside throughout the film.