During the end of the Cretaceous era, an Iguanodon mother is forced to abandon her nest during a Carnotaurus attack. The one surviving egg journeys through several predicaments, before ending up on lemur island, where Plio names the hatched baby Aladar and raises him. Years later, Aladar and the lemurs take part in a mating season, where Zini goes without a mate. After the season ends, a meteor strikes and destroys the island, leaving Aladar, Plio, Yar, Zini and Suri, as the only survivors when they swim to the mainland. The family mourns for the loss of all lemurs before moving on.
Slate and Co. Senior Executive Cliff Vandercave (Kyle MacLachlan) and secretary Miss Sharon Stone (Halle Berry) look at the company workers in the gravel pits while discussing their plan to swindle the company of its vast fortune and flee, but decided that they need someone to take responsibility for it. Fred Flintstone (John Goodman) loans his best friend and neighbor Barney Rubble (Rick Moranis) money so that he and his wife Betty (Rosie O'Donnell) can adopt a child named Bamm-Bamm, who can only pronounce his own name. Although the child is initially difficult to control due to being raised by Mastadons, as well as being superstrong, he eventually warms up to his new family. Barney vows to repay his friend, but Fred is visited by his mother-in-law, Pearl Slaghoople (Elizabeth Taylor), who objects to his decision. However, Fred's wife Wilma (Elizabeth Perkins) remains supportive of his decision.
In an alternate timeline in which Earth was never hit by an asteroid and dinosaurs never became extinct, a young Apatosaurus named Arlo loses his father in a tragic accident. One day, Arlo falls into a river and gets knocked out by a rock, finding himself far away from his home. While trying to find a way back to the Clawed-Tooth Mountains, he befriends a human caveboy that he names Spot.
Paleontologist Zack takes his nephew Ricky and niece Jade on a fossil hunt, giving the sullen Ricky his Gorgosaurus tooth while he and Jade go to the fossil bed. Alone, Ricky is met by a talking rook, who morphs into Alex the Alexornis bird, who takes the story back to the Cretaceous period 70 million years ago. Patchi is the smallest of his litter of Pachyrhinosaurus hatchlings, and is often bullied by his large, proud older brother Scowler. Their father Bulldust is the leader of the herd. Patchi is attacked by a Troodon and receives a distinctive hole in his frill when he ventures outside the nest one morning. Alex, serving as Patchi's mentor, tries to help Patchi impress a female Pachyrhinosaurus named Juniper, but her herd soon migrates south without him. Bulldust soon follows suit, moving his herd to the south, but when they try to pass through a dense forest, they are forced to flee when a forest fire erupts. Taking advantage of the chaos, Gorgon the predatory Gorgosaurus attacks the fleeing Pachyrhinosaurus, and while his pack kills their mother and siblings, Patchi and Scowler witness Gorgon killing Bulldust.
Dennis and his friends find a dinosaur bone in his backyard, dubbed by him as the "Dennissaurus". The discovery makes life miserable for everyone, as scientists, reporters, and amusement park operators overrun the neighborhood.
The plot revolves around 16-year-old Ally Hayden (Liz Stauber), the daughter of Dr. Donald Hayden (Peter Horton), a world-famous paleontologist and museum curator. She loves dinosaurs and longs to be able to accompany him to one of the nearby paleontological digs, but her father thinks this is too dangerous and she has to settle for giving museum tours instead.
In the opening scene, Max Anderson (Jean-Michel Paré) is being pursued by a Giganotosaurus. Max then comes across a fissure vent. When he tries to jump across, he falls while calling out the name of his brother. Ten years later, Max's brother volcanologist Trevor Anderson (Brendan Fraser) is visited by Max's son/Trevor's 13-year-old nephew Sean Anderson (Josh Hutcherson). In a box of items that belonged to Max is a book, Journey to the Center of the Earth by Jules Verne. Notes written by Max are found inside the book.
Near the end of the Cretaceous, a series of catastrophic events are causing intense drought, and several herds of dinosaurs seek one of the last livable places, a paradise known as the "Great Valley." Among these, a diminished "Longneck" herd gives birth to a single baby, named Littlefoot (Gabriel Damon). Years later, Littlefoot plays with Cera (Candace Hutson), a "Three-horn," who was trying to smash a beetle until her father (Burke Bynes) intervenes; whereupon Littlefoot's mother (Helen Shaver) names the different kinds of dinosaurs: "Three-horns," "Spiketails," "Swimmers," and "Flyers," and states that each has historically remained apart. That night, as Littlefoot follows a "hopper," he encounters Cera again, and they play together briefly until a "Sharptooth" appears. He attacks them, before Littlefoot's mother comes to their rescue. During the fight, she suffers severe back and neck injuries from the Sharptooth's teeth and claws. At that same time, an "earthshake" opens a deep ravine that swallows up the Sharptooth and divides Littlefoot and Cera from their herds. Littlefoot finds his dying mother, and receives her final words of advice in favor of his intuition.
Une créature géante se manifeste dans la baie de Tokyo, avant de faire surface et de terroriser la ville. Le cabinet ministériel se réunit d'urgence, mais le Premier Ministre est incapable de prendre une décision. Les radiations mesurées sur le passage de la créature démontrent qu'elle est le triste produit d'une contamination. Plus tard, elle évolue et revient sous une forme encore plus monstrueuse, réduisant Tokyo en poussière. Devant l'ampleur de la menace, les États-Unis décident d'utiliser l'arme nucléaire sur le Japon si ce dernier échoue à éradiquer la menace, réveillant le spectre des bombardements d'Hiroshima et de Nagasaki. Une équipe de chercheurs se regroupe alors en marge des décisions du Cabinet pour déterminer comment éliminer le monstre, surnommé "Godzilla". La France et l'Allemagne finiront par s'en mêler à leur tours.
Le film est composé de sept séquences illustrant huit morceaux de musique classique, réorchestrés et dirigés par le chef d'orchestre Leopold Stokowski à la tête de l'Orchestre de Philadelphie. La dernière séquence illustre deux morceaux et un intermède sépare la séquence 4 et 5. Chaque séquence est précédée d'une courte introduction où l'orchestre est en ombre chinoise.
Pompous paleontologist Rick Marshall has a low-level job at the La Brea Tar Pits, three years after a disastrous interview with Matt Lauer of Today became a viral video and ruined his career. Doctoral candidate student Holly Cantrell tells him that his controversial theories combining time warps and paleontology inspired her. She shows him a fossil with an imprint of a cigarette lighter that he recognizes as his own along with a crystal made into a necklace that gives off strong tachyon energy. She convinces him to finish his tachyon amplifier and come help her on a seemingly routine expedition to the cave where Holly found the fossil, which is in the middle of nowhere. With cave gift shop owner Will Stanton they raft into the cave, where Marshall has detected high levels of tachyons. He activates the tachyon amplifier, triggering an earthquake that opens a time warp into which the raft falls. The group finds themselves in a desert, filled with various items from many eras, and without the amplifier. They rescue a primate-like creature, Cha-Ka of the Pakuni tribe, who becomes their friend and guide.
Young bachelors and best friends Fred Flintstone (Mark Addy) and Barney Rubble (Stephen Baldwin) have recently qualified as crane operators at Slate & Company. Soon to be employed, now they want dates, and little green alien The Great Gazoo (Alan Cumming), exiled to Earth by his species, offers to help, although only they can see him. Meanwhile, Wilma Slaghoople (Kristen Johnston) wants a normal life and activities, like bowling, despite her controlling mother Pearl (Joan Collins) who wants her to marry smooth casino-owner Chip Rockefeller (Thomas Gibson). Wilma angrily runs away to Bronto King in Bedrock. Waitress Betty O'Shale (Jane Krakowski) mistakes her as "caveless", and offers to share her apartment, and gets her a job.
Suneo shows everyone a fossilized claw of a Tyrannosaurus rex and Nobita is angry that he doesn't get a look. Nobita claims that he will be able to find a living dinosaur. Panicking, Nobita researches on dinosaurs and starts digging in a hill. But then, a landlord shouts at him and makes him dig a hole in the ground to dispose of some egg shells. Nobita unearths a rock shaped like an egg. Using the time-wrap, he returns the rock into its former form and plans to hatch the egg. He spends a day and night wrapped tightly in a blanket with it on his futon, despite it being the peak of summer. A "Futabasaurus" comes out, and Nobita decides to name the plesiosaur Piisuke. Suneo and Gian come looking for Nobita but because Piisuke is still too small, Nobita doesn't show them the plesiosaur and instead makes a deal with them. If he cannot show them a real dinosaur, he would have to eat spaghetti through his nose. Meanwhile, Nobita and Piisuke form a strong bond between them with Nobita working very hard to make sure the baby plesiosaur is well looked after, feeding it his own dinner of sashimi and playing with it. He grows very attached to Piisuke.