In this movie Scrat meets Scratte and there is love in the air - between them and the nut. Scratte believes Scrat have saved her and she is attractive to him and they fall shortly in love, which actually breaks the nut. The complications between the three set the scene.
Ellie the mammoth is near labour and the herd dissolves. Diego the saber-toothed cat leaves them. Sid the sloth then decides to start his own family and steals three eggs. They hatch and the large mother returns. Sid argues with her about «his» kids. The problem is that she is a T-rex, and she forces the four down to a new underworld of dinosaurs.
The herd is regathering to save Sid, but they need help from Buck the Weasel to get Sid the new mother back.
The third movie is a bit funnier than the first two. And the graphics are far better than the first movie.