Offering up a sort of alternate prehistory on what might have happened bad the theoretical asteroid that hit Earth 65 million years ago that wiped out all of the dinosaurs not occurred, dinosaurs are the ones that have advanced to learn how to speak and perform agriculture. We spy Poppa and Momma awaiting the hatching of three of their eggs, springing forth unruly Buck, enthusiastic Libby, and overly jumpy runt Arlo. Buck and Libby take readily to their parents instructions, but Arlo is always lagging behind in his rites of passage, primarily out of his innate sense of fear, causing Poppa to have to take a more aggressive stance with the tyke to get him where he should be in life. When their silo of corn is constantly being raided by an unknown critter, Arlo is tasked with putting an end to it. After setting his trap and going in for the kill, Arlo discovers a feral Neanderthal boy with dog-like tendencies, and finds he can't bring himself to do it. Mishaps arise that see Arlo and Spot (as Arlo has dubbed him) washed away in a river and subsequently quite far from home, forcing them to make the long, perilous journey back through strange lands full of stranger creatures.