A Carnotaurus ambushes and chases an infant Parasaurolophus, and the stampede of the dinosaurs force an Iguanodon mother to abandon her nest. The one surviving egg journeys through several predicaments via the flight of a Pteranodon, before ending up on a far away island populated by lemurs. Plio names the hatched baby Aladar and raises him. Years later, Aladar and the lemurs take part in the mating ritual, where Zini goes without a mate. Moments after the ritual ends, a giant meteor strikes and spreads numerous exploding fireballs that destroy the island and kill the rest of the lemurs. Aladar, Plio, Zini, Yar and Suri flee and jump across the sea to the mainland, and mourn for their losses before moving on.
While crossing deserted wastelands, they are ambushed by a pack of Velociraptor. After escaping from them, the family come across a remaining multi-species herd of dinosaurs led by Kron and Bruton, who are on a journey to reach the "Nesting Grounds", a valley said to be untouched by the meteor. As Aladar and the lemurs befriend a trio of elderly dinosaurs, Kron permits them to follow behind them. Together, they migrate to a lake they have relied on for past trips. Though it has seemingly dried up by the meteor, Aladar and Baylene discover the water is buried under the lake's dried surface, thereby saving the herd from dehydration. Impressed by Aladar's compassionate ways, Neera begins to fall in love with him. Meanwhile, two Carnotaurus pick up the herd's trail and begin stalking them for food. They attack Bruton, who barely escapes and warns Kron that they are coming. Kron picks up the pace and quickly evacuates the herd, leaving Aladar's family, the older dinosaurs and Bruton behind, while the Carnotaurus are in pursuit some distance away. During a rainstorm, the stragglers spend the night in a cave and Plio heals Bruton, before being found and attacked by the Carnotaurus. Bruton saves the others and sacrifices himself to kill one of the Carnotaurus by causing a cave-in. As the rest of the group move through the cave, the second Carnotaurus survives and resumes its search for the herd.
Aladar loses hope when they reach a dead end, but the others convince him to keep going, relating how he inspired them to do the same. After they knock down the dead end together and successfully find the Nesting Grounds on the other side, Eema sees a large wall of rocks from a landslide blocking the original entryway to the valley. Knowing that the herd will die attempting to climb over it, Aladar rushes off alone to find them, but the Carnotaurus pursues him. As Aladar arrives to warn the herd about the sheer drop and suggests the safer way to the valley, Kron angrily attacks him. Neera stops Kron, and the herd, seeing Kron's selfishness, decides to abandon him, taking Aladar as their new leader. As they prepare to leave, the Carnotaurus confronts them. Aladar rallies the herd to stand together, and they bellow their way past the predator, who follows Kron. Aladar and Neera fight against the Carnotaurus until it falls off the cliff to its death. Kron dies from his injuries, with Aladar and Neera mourning for him.
The herd are led back to the Nesting Grounds as their new home. A new generation of dinosaurs hatches sometime later, along with Aladar and Neera's children, and the lemurs find more of their kind.
What do the stragglers spend a night in?
A cave