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Trapped in a storm, a group of rock climbers seeks shelter in a cave, and there meet an elderly scientist, who tells them the story of the prehistoric carvings found on the cave walls.  The carvings tell the story of a boy, Tumak, and a girl, Loana, from two different tribes.

Tumak, a member of the brutal Rock tribe who rule by power and violence, wanders afield from the harsh cliffs of his land to the lush valleys of the gentle Shell people, where he is found by Loana.  At first puzzled by the generosity of the Shell people, Tumak is able to repay their kindness by saving one of the Shell children from an attack by a ferocious dinosaur.  However, when Tumak steals a spear from a member of the tribe, he is banished, and Loana leaves her people to accompany him.

They return to Tumak's people, where Loana's gentleness sets an example that transforms the cruel nature of the Rock people.  All is idyllic until a volcano erupts and traps Loana and the other members of the tribe in a cave guarded by a dinosaur.  In order to save them, the Shell people join the Rock people; during a fierce battle to kill the beast, the two tribes are united.