The Land Before Time V: The Mysterious Island is a 1997 direct-to-video animated film directed by Charles Grosvenor.
After a cloud of “Swarming Leaf Gobblers” (locusts) descends upon the Great Valley, devouring all the plants and leaving it a barren wasteland, the inhabitants have no choice but to leave and seek another place where they can survive until the plants in the Great Valley have grown back. However, the swarming leaf gobblers have left a path of devastation behind them, leaving no food for the dinosaurs to find. After wandering for many days through the desolation, the herd quarrels and threatens to separate.
Not willing to let the grownups' decision separate them, Littlefoot, Cera, Ducky, Petrie, and Spike set out on their own to find food for the herd in order to keep it together, on the basis that the adults will follow their children. After a long walk, during which they try to leave a distinct trail for the grownups, they are at the edge of giving up the endeavor as no food is in sight, when they suddenly reach something they have never seen before; the "Big Water" (ocean). Nearby, they discover a verdant island connected to the mainland by a very thin land bridge. While the group is crossing the bridge, they are surprised by an earthquake that nearly drowns them and destroys most of the bridge, trapping them on the island.
Unable to call the attention of their families, who have indeed followed their trail to the beach, the children try using Cera's idea to escape from the island on a floating log (which makes her seasick). However, the attempt fails when a hungry Swimming Sharptooth (resembling a Cretoxyrhina) attacks, and the kids barely make it back to the island. They find a spot to sleep for the night, though longing to be with their families brings them a case of insomnia which lasts them most of the night.
The next morning, Littlefoot wakes up and sees the shadow of a Sharptooth. He wakes up the others, and they flee, with the still unseen Sharptooth chasing them. Soon they are cornered, however, the Sharptooth turns out to be Chomper, the baby Sharptooth they hatched in The Land Before Time II: The Great Valley Adventure. At first, Chomper wants to introduce his parents to the gang, but the latter refuses to meet them. Chomper's parents find their son (while the gang hides in a nearby bush) and tell him that dinner is ready. Chomper asks if he can invite some friends, but to his silent shock and dismay, they assume that the friends are for dessert. Chomper's father smells a Longneck close at hand (Littlefoot), but Chomper stops him with the alibi of eating Longneck for breakfast and that he burped. Buying the alibi, they tell Chomper to come along with them. Telling them he will not be long, Chomper is left with no other choice but to assist the gang in hiding from his parents.
Despite all his efforts to hide his friends, make them feel comfortable, and provide them with green food (plants), Cera bears and openly displays a great distrust for Chomper for the fact that he is a Sharptooth. This grieves Chomper, who then departs. Littlefoot follows to apologize, but they are interrupted by Chomper's mother. She nuzzles her son gently, ignoring Littlefoot (whom she presumes is prey). Littlefoot is amazed that Sharpteeth are capable of generating or experiencing love.
Unaware of Chomper, his parents, or the main characters, another Sharptooth (resembling a Giganotosaurus) has been living on the island. He surprises the children in their hiding place, chases them out, and ends at the edge of a cliff above the ocean, where he has the children trapped. At this moment Chomper shows up, to defend the others, and is soon followed by his parents, who begin a fierce fight with the foreign Sharptooth. The Giganotosaurus shows amazing persistence, jumping over a ditch and lifting over a rock the gang were hiding under in an attempt to get at them, and fights off both of Chomper's parents with his claws and tail, including knocking out Mama Sharptooth. The fight ends when he is knocked over the edge of the cliff by Chomper’s father before the Giganotosaurus could reach his mate. While falling, he sweeps Chomper off the cliff and into the ocean. Seeing this, and not wanting to forsake his friend, Littlefoot plunges into the water to save Chomper. The sharptooth continues to attack them in the water, but is ultimately washed away by the current and presumably drowns.
Both are rescued by a friendly Plesiosaur (resembling an Elasmosaurus) named Elsie, who sets the two of them ashore. The main characters are at first worried that Chomper's parents will eat them, but the sharpteeth are thankful for the rescue of their son, and therefore promise that they will do them no harm. Even under the Sharpteeth's protection, Littlefoot and the others miss their families and are anxious to get back home. Overhearing their trouble, Elsie proposes to carry Littlefoot and the others back across the Big Water, an offer they gladly accept despite Chomper’s disappointment over their departure.
After a bit of reunion between the herd and the main characters, the adults show them that they have found a lush, green place at the shore, where they may live until the Great Valley is regrown, at which time they shall return home.