The story of Apatosaurus famers "Henry" and "Ida" have 3 children "Libby", "Buck" and "Arlo",who has trouble adjusting to farm life. While his successful siblings are allowed to make their mark on the family's corn silo. Henry saft Arlo from a flash flood before being swept away and killed. Without his father Arlo should more of the workload. He spots the caveboy and both fall into a river. Arlo Knocked unconscious. he find himself far from home and the cave boy appears with food for him. Arlo calls him "Spot" Arlo runs away in fear and loses the riverbank he has been following home. After that they have found many exiting event.Both occur bound together. As they approach Arlo's home ,Arlo pushes spot to join his kind and they share a tearful goodbye,Arlo finally arrives home to his mother and siblings,and makes his mark on the silo between those of his mother and father