A narrator (Pat Hingle) opens the film by saying: "Once upon this same earth, beneath the same sun, long before you, before the ape and the elephant as well. Before the wolf, the bison, the whale, before the mammoth and the mastodon, in the time of the dinosaurs," a drought is occurring and some dinosaurs are heading to the "Great Valley", a land still lush and green.
A "Longneck" (Apatosaurus) herd gives birth to a single baby, named Littlefoot (Gabriel Damon). Years later, Littlefoot comes across Cera (Candy Hutson), a "Three-horn" (Triceratops), practicing head-butting while trying to smash a beetle with her horn. The dinosaurs play together until Cera's father, Topsy (Burke Byrnes), intervenes. Littlefoot's mother (Helen Shaver) explains the different kinds of dinosaurs: "Three-horns, Spiketails, Swimmers, Flyers" and that they never do anything together, and it's always been that way, but she promises Littlefoot that there will be other longnecks for him to play within the Great Valley.
That night, as Littlefoot follows a "hopper" (frog), he encounters Cera again, and they play together briefly until a "Sharptooth" (Tyrannosaurus rex) (Frank Welker) attacks. During their escape, Littlefoot accidentally blinds Sharptooth in one eye with a thorn. Littlefoot's mother battles with Sharptooth and suffers severe injuries, but defeats him by pushing him into a deep chasm. At the same time, an "earthshake" (earthquake) occurs, opening a deep ravine in the ground. It swallows up the Sharptooth and many other dinosaurs, separating Littlefoot and Cera from their herds. Littlefoot finds his mother when the earthquake ends, but she is near death. Just before she dies, she gives Littlefoot instructions on how to get to the Great Valley: to follow the "bright circle" (sun) past the "great rock that looks like a longneck" and then past the "mountains that burn" (volcano).
Now feeling depressed and confused, Littlefoot by chance slides down a ravine, where he meets an old Polacanthus named Rooter (Pat Hingle), who consoles him upon learning of his mother's death. After mourning for some time, Littlefoot begins to search for the Great Valley. He encounters Cera again and tries to get her to join him, but she refuses. Littlefoot meets a young "Bigmouth" (Saurolophus) named Ducky (Judith Barsi), who has also lost her family in the earthshake. They journey on together, and as they try to find food, they encounter an aerophobic "Flyer" (Pterodactyl) named Petrie (Will Ryan), who joins them on their quest.
Meanwhile, Cera finds Sharptooth's body and begins playing with it. However, it is not dead, only unconscious, causing Cera to flee in terror when he wakes up. Cera later bumps into Littlefoot, Ducky, and Petrie and warns them of Sharptooth, but Littlefoot is convinced that Sharptooth is dead. As Cera describes the encounter (exaggerating her bravery), she accidentally flings Ducky near a patch of grass, which has a hatching egg containing a baby "Spiketail" (Stegosaurus). Ducky names him Spike and brings him into their group.
Seeking the Great Valley, they find a river leading to a cluster of trees, which is abruptly depleted by a herd of starving Diplodocus. Searching for remaining growth, they discover a single leaf-bearing tree and obtain food by stacking up on top of each other and pulling it down. Cera remains aloof and arrogant, boasting that she is independent, but at nightfall, she, along with the others, gravitates to Littlefoot's side for warmth and companionship. Sharptooth attacks them in the morning. They escape through a cave tunnel too small to admit him, then discover the Longneck-shaped monolith mentioned by Littlefoot's mother.
Although they pass other landmarks, such as a string of volcanoes, Cera grows impatient as the search begins to yield no results. She quarrels with Littlefoot, causing a schism in the little herd following a fight between the two in which Cera drives her head into Littlefoots stomach, butts him, launches him back first into a solid wall and easily overpowers him in several situations. Littlefoot continues in the direction he was told, while the others follow Cera, who goes another way, which she claims to be the easier way. As Ducky, Spike and Petrie fall into danger involving lava barriers and a tar pit, Littlefoot rescues them. They find Cera being harassed by a pack of Pachycephalosaurus, and, having been coated in tar, scare them away. Ashamed and humiliated, Cera, still unwilling to admit that she had gone the wrong way, goes off to be alone.
While frolicking in a pool of water, Littlefoot and his friends spot Sharptooth in the distance. Surmising that Sharptooth cannot swim, Littlefoot formulates a strategy to lure him into the deep end of the pond, and push a nearby boulder onto him, drowning him. As Ducky lures him to the water, Littlefoot and Spike have trouble moving the rock. During the proceeding struggle, a draft from Sharptooth's nostrils enables Petrie to master his powers of flight. The plan nearly fails when Sharptooth leaps on top of the boulder, until Cera rejoins the group, allowing Littlefoot and his friends to push both Sharptooth and the boulder into the water below. However, as he falls, he grabs Petrie in his jaws and drags him into the pond with him. As the young dinosaurs mourn the loss of Petrie, he re-emerges, having escaped a similar fate to Sharptooth.
Littlefoot encounters a large cloud that appears to be his mother in some sort of spirit form. As he laments to her that the journey is just too hard, she departs. Littlefoot follows the cloud through a cave and emerges just as the sunlight illuminates the landscape beneath him: He has found the Great Valley at last. The others join him and hurry down to the Valley, where the children's surviving relatives are already settled. Petrie impresses his family with his new-found flying ability, as Ducky introduces Spike to her family, who adopt him. Cera reunites with her father, and Littlefoot joins his grandparents. As Littlefoot reminisces on the events of the story, from his hatching all the way up to when he encounters his mother's spirit, Cera calls him to play. The group then races to the top of a hill and embrace each other in a group hug as the narrator closes the film by saying: "And they all grew up together in the valley generation upon generation. Each passing on to the next, the tale of their ancestor's journey to the valley long ago."
- In a picture book, The Search for the Great Valley, there is an alternate ending in which, right after Littlefoot leaves his friends for listening to Cera instead of him, the longneck meets the ghost of his mother, and encounters the Valley, only to realize that he should turn back to look for his friends, which he did.
- This is also a work done by George Lucas, who is famous for his work on Star Wars.
- To date, An American Tail and this film are currently the only two feature-length Don Bluth films not owned by 20th Century Fox.
- The film generated many direct-to-video sequels. Currently, there are thirteen sequels in circulation. The sequels depart from the style of the original significantly by adding "sing-a-long" musical numbers akin to Disney animated films, and toning down the intensity seen in the original film. Don Bluth and his animation studio have no affiliation with any of the film's sequels. The sequels have generally been met with a mixed reception with several fans of the original disregarding the sequels, while some have embraced the sequels into the canon of the story.
- Track listing
- "The Great Migration"
- "Sharptooth and the Earthquake"
- "Whispering Winds"
- "If We Hold On Together"
- "Foraging For Food"
- "The Rescue/Discovery of the Great Valley"
- "End Credits"