King K. Rool is a crocodile and he has a navel, in real life crocodilians and other reptiles do not possess navels, this trait is only found in mammals, more specifically placental mammals.
It is not possible for Donkey Kong and Diddy Kong to breathe underwater while scuba diving without oxygen tanks as they are mammals. If Donkey Kong and Diddy Kong tried this in real life, they would both drown.
The Kritters in variations that can jump, their gold-plated armor disappears when they do so, and reappears when they land.
In one of the game's artworks, Diddy Kong is shown riding on Donkey Kong like the team-up ability that was not present during gameplay until the later two games in the DKC trilogy.