Alex: I wanna prove to my dad that I'm a *real* lion.
Marty: As opposed to what, a *chocolate* lion?
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.
If you look at the birth mark on both Alex's and Zuba's right paws they are in the shape of Africa, including the island of Madagascar which is off the east coast of Africa.