Mammoths Manny and Ellie are going to be parents, which is splitting the unique flock consisting of them, Sid the sloth, Diego the saber-tooth tiger and Crash and Eddie the possums. Diego feels he has lost his somewhat tougher side and thinks it is time to move on, while Sid wants to become a parent like Manny and Ellie. The opportunity arises when he finds three apparently abandoned eggs. Problems mount up quickly as it turns out that the eggs belong to a dinosaur. The differences in the flock must be set aside as Sid has to be saved from the dinosaur that takes him to a valley filled with prehistoric dinosaurs and a very special weasel called Buck. In addition, as always, we get a happy reminder of Scrat the squirrel who falls in love with something other than a nut for the very first time Scratte seduces Scrat in this new adventure, but does he manage to devote all his attention to her?