After their unforgettable jouey in the previous installment, the "one-of-a-kind" herd is now settled and content. First, there's the mammoth couple Manny and Ellie, eagerly awaiting the arrival of their first child. Manny finds himself in a state of stress, wanting everything to be perfect, safe, and beautiful for the upcoming birth.

Diego, the saber-toothed tiger, decides to leave when he realizes he's losing his wild side while living with Manny's family, even failing to catch a single deer. Sid, the sloth, also yeas to become a parent upon seeing Manny about to have a baby.

By chance, Sid discovers some eggs buried beneath the ice, choosing to keep them despite Manny's advice to retu them. This results in the hatching of three T-Rex dinosaurs, who mistake Sid for their "mom" and joyfully adopt him.

Disaster strikes when the T-Rex mother arrives to reclaim her offspring, taking all three "kids" and Sid away. Reluctantly, Manny, Ellie, the possum brothers Crash and Eddie, and Diego set out to rescue their friend.

Following the T-Rex's trail, they stumble upon a secret tunnel leading to a tropical world, where dinosaurs, thought to be extinct, still thrive. Almost lost in this entirely different world, the group is attacked by dinosaurs, only to be saved by a new character - a daredevil weasel named Buck, who has lived here for years.

Buck agrees to help the newcomers find Sid. Thus begins their adventure into this new world - the world of dinosaurs...

Alongside the main characters' jouey, the familiar squirrel Scrat continues his relentless pursuit of acos. The clumsy squirrel unwittingly encounters an unexpected rival - a female squirrel named Scratte. Will his lifelong passion for acos triumph, or will the allure of the "seductive" Scratte prevail?