The action takes place 20 thousand years ago. To avoid the approaching cold due to the onset of the ice age, animals migrate to the South. However, some of them still decide to stay — the lonely, sullen mammoth Manfred, as well as the reckless sloth Sid.
By chance, this couple comes across a human cub. They decide to return it to the people and go on a journey. Along the way, they meet a saber-toothed sly tiger. And now this fun company will have fun adventures!
Manny, full name Manfred (Ray Romano), is a surly woolly mammoth who considered himself the last of his kind on Earth until he met Ellie in a previous cartoon. While waiting for the arrival of his and Ellie's child, Manfred refuses the usual free lifestyle, but becomes overly nervous, suffers from the overprotection of Ellie and is paranoid about the future birth of a mammoth.
Sid, full name Sidney (John Leguizamo), is a lazy, clumsy and always annoying sloth (megatherium), who dreams of proving himself. In the third cartoon, Sid is filled with envy for the future family of Manny and Ellie, dreaming of having his own. Therefore, taking three dinosaurs to raise, he completely refuses to return them to their mother, which is why he gets into the world of dinosaurs and creates problems for his friends, who are forced to go to save him.
Diego (Denis Leary) - a proud and independent saber-toothed tiger (from the genus smilodon), Diego began to notice that he became very bad at hunting, living in the company of his friends. When Manny and Ellie began to expect the arrival of their child, Diego felt that he no longer has a place among them, because he is becoming too "soft", and decides to leave. However, when he learns that sid has been kidnapped by a dinosaur, he goes along with everyone to rescue Him. As a result, helping friends and fighting for them, Diego realizes that he has something to stay in their pack for.
Ellie (Queen Latifah) - a mammoth who became Manfred's companion and a friend of Sid and Diego. Usually cheerful and carefree, Ellie, however, found time to prepare for the birth of her cub and, even being pregnant, did not want to stay safe on the surface, and together with friends goes to save Sid.
Crash and Eddie (Seann William Scott and Josh peck) are two bully possums, Ellie's half — brothers. Having met Buck in the world of dinosaurs, Crash and Eddie began to have fanatical respect for this tireless and fearless beast.
Tank, the full name of Buckminster (Simon Pegg), — the affection; fierce and fearless dinosaur hunter, a hermit who lives with them in the underworld. Buck saves the main characters from being attacked by monsters and agrees to lead them to the lair of the Tyrannosaurus mother to save Sid. Buck doesn't have his right eye, which he lost in a fight with the most dangerous of the dinosaurs, which he calls Rudy; he made a dagger out of the same monster's tooth. Buck, who is used to living alone, often behaves like a madman (which in part he is).