In a vast dinosaur breeding ground, a young Parasaurolophus inadvertently reveals the presence of a Carnotaurus, sparking a chaotic stampede. Amidst the chaos, an Iguanodon mother is forced to abandon her nest, which is tragically crushed by the predator's pursuit. The sole surviving egg is captured by an Oviraptor, leading to a remarkable journey through a variety of terrains, until it reaches a tropical island inhabited by prehistoric lemurs. Here, Plio, the daughter of the patriarch Yar, names the newly hatched baby Aladar and takes him under her wing, despite Yar's initial disapproval.
Fast forward to Aladar's adulthood, where he and the lemurs partake in a lively mating ritual, though his friend Zini struggles to find a mate. Just when the festivities conclude, calamity strikes as a meteor shower engulfs the sky, resulting in a colossal meteoroid crashing into the Earth. The explosive shockwave devastates the island, leading to the loss of nearly the entire lemur population. Aladar, alongside Plio, Yar, Zini, and Suri, narrowly escapes the disaster by leaping across the ocean toward the mainland. They look back at their obliterated home, grieving for their loved ones as they resolve to press on.
As they traverse the desolate wasteland, the group faces aggression from a pack of Velociraptors. After a harrowing escape, they encounter a mighty herd of dinosaurs under the leadership of Iguanodons; led by Kron and his second-in-command Bruton. This herd is on a quest for the renowned "Nesting Grounds," a sanctuary untouched by the catastrophic meteor fallout. Following a night of rest, Aladar and the lemurs forge bonds with the gentle Baylene, an elderly Brachiosaurus, her companion Eema the Styracosaurus, and Url, her loyal dog-like Ankylosaurus.
The next day, the herd arrives at a lake that, unfortunately, has run dry. Kron commands the herd to continue moving until Aladar and his companions discover a hidden water source beneath the surface, quenching the herd's thirst. Impressed by Aladar's kindness, Kron's sister Neera begins to form a connection with him. Meanwhile, two persistent Carnotaurus have been tracking the herd, intent on turning them into their next meal. An expedition for water leads to Bruton being ambushed and Duke, a scout, falling prey to the Carnotaurus. Though Bruton escapes, panic ensues among the herd as it is alerted to the imminent danger.
During a torrential downpour, Aladar and the group encounter Bruton, who had been left behind by Kron. Finding refuge in a cave, they are suddenly attacked by the Carnotaurus. In a courageous act, Bruton sacrifices himself, causing a cave-in that eliminates one of the attacking predators. The surviving Carnotaur swears revenge, prompting Aladar and his friends to flee deeper into the cave, ultimately breaking through to arrive at the Nesting Grounds.
Upon exploration, they discover a massive barrier of boulders blocking the entrance to the valley. Realizing the herd may never reach safety, Aladar rushes back to rescue them, pursued by the vengeful Carnotaurus. He catches up with Kron and the herd, proposing an alternate route. However, Kron allows his pride to cloud his judgment and dismisses Aladar’s insight. An explosive confrontation ensues between Aladar and Kron, only to have Neera intervene in support of Aladar. Ultimately, the herd chooses to abandon Kron and follow Aladar toward safety.
As they prepare to depart, Aladar, Neera, and the remainder of the herd face a final stand against the furious Carnotaurus. Rallying the group, Aladar inspires them to band together, driving back the predator. In a dramatic twist, Kron, trying to escape the Carnotaurus, finds himself at the edge of a cliff and realizes too late that Aladar’s plan was sound. He fights valiantly but suffers fatal injuries. In a desperate bid to protect her brother, Neera intervenes but faces overwhelming odds. Aladar bravely confronts the Carnotaurus, leading to a climactic showdown that results in the predator's fall.
With Kron gone, Aladar becomes the new leader, guiding Neera and the herd to the Nesting Grounds. Time passes, and a new generation of dinosaurs hatches, including the offspring of Aladar and Neera. The lemurs, too, discover more of their kin, marking the start of a promising new life together in this serene haven.
