As told in deleted scenes on the DVD release, the Nesting Grounds were first discovered by an Iguanodon named Old Gotama, whose fossilized remains still remain in the area. Since then, dinosaurs of numerous species have migrated to and from the area as a collective herd.
In the opening of the film, a nesting period in the Nesting Grounds turns from peaceful to chaotic when a Carnotaur sends various dinosaurs scattering and begins the journey of Aladar's egg to Lemur Island. This all started when an Oviraptor noticed Aladar's egg left unharmed and intact in one of the nesting sites. It then took the egg and hurried off into the jungle with it. However, before it could start eating the egg, another Oviraptor swiped it from its grasp, and the two Oviraptors began brawling for the egg until their fingers eventually lost their grips onto the egg, which fell into the river below. A Pteranodon then scooped up the egg from the river and carried it to its nest on Lemur Island, only to be attacked by two birds, causing it to drop the egg onto the island.
Years later, after a meteor destroys the island, Aladar and hisadoptedlemurfamily manage to make it to the mainland, and then follow a saurian migration group and their desperate bid to find sanctuary in the Nesting Grounds. The earlier catastrophe has blocked the main entrance off with an impassable wall of rocks, but an alternative route through a cave is opened up by Aladar and his friends.