During a rafting excursion of an uncharted river canyon, Professor John Butler, wife Kim, kids Katie and Greg and family dog Digger get caught up in a mysterious whirlpool and resurface in a world of prehistoric creatures. Now everyday is an exercise in survival for the adventurous Butler family. They befriend a helpful cave-dwelling family and together must contend with an angry brontosaurus and a dangerous sabertooth tiger - and don't forget the earthquakes and volcanoes!