70 million years ago, a diminutive underdog dinosaur named Patchi triumphs against all odds to become a hero for the ages. The runt in his family of Pachyrhinosauruses, he has to use his wits and heart to compete with his larger brothers and sisters, particularly Scowler, the alpha male of the group. Their father Bulldust is leading the herd on its annual migration when he and sons Patchi and Scowler are separated from the rest of the family by a forest fire and then trapped by a predatory Gorgosaurus. Bulldust sacrifices himself to save his sons, and their mother perishes in the fire. Now alone in the world, the two brothers must fend for themselves and their rivalry grows as they become powerful adults. But when the migration leads to their greatest battle, Patchi summons his inner courage and strength to become the leader he was born to be.