Kenneth Mars

Grandpa tells Littlefoot about their mythical hero called the Lone Dinosaur. Sarah gets two little lively cousins to take care of. Later, the kids accidentally chip the lucky Saurus Rock, and need to fix it before the bad luck hits.

When the dinosaur families get trapped in a valley by an ice storm, one family of "spike tail" dinosaurs volunteers to leave since they consume more food than the others. Meanwhile, the young dinos and a new adult dinosaur named Mr. Thicknose, head out to bring back their friend Spike, who has left his friends to be with members of his own species.

In search of some adventure in their safe and peaceful valley, the five dinosaur friends make a hideaway. From there, they spot two thieves in action, stealing an egg from one of their broods. They chase them down and manage to recover the egg without its parents noticing, but in the process, accidentally create an opening into the valley, allowing two dreaded Sharptooths in. Everyone must fight them off together to preserve their peaceful way of life.