A nearby eccentric Styracosaurus (Peter Sohn), also impressed with the cave-boy's physical prowess, tries to give him a name, but when Arlo calls him 'Spot', he responds to it. The cave-boy fights and repels the snake, an act which amazes Arlo. The cave-boy then leads Arlo to a berry tree where they are both attacked by a snake. The next day, the cave-boy finds and frees Arlo, and eventually gives him some berries to eat. Waking up, Arlo is dismayed to find himself far from home and tries to survive on his own with minimal success, leaving himself trapped under a boulder.

After spotting the same cave-boy inside the silo, Arlo, blaming him for his father's death, chases him until both of them fall into a river, where Arlo hits his head on a rock and is knocked unconscious. Without his father, Arlo must help his mother with harvesting crops before the first snow. After Arlo injures himself, Henry decides to turn back just as a flash flood occurs and a massive rapid appears, but Henry only manages to save Arlo before he is swept away and killed. Heavily disappointed, Henry has Arlo accompany him to track the cave-boy through a ravine where it begins to rain. While Arlo is on guard, the trap manages to capture a feral cave-boy, but Arlo is too reluctant to kill him and sets him free. In order to give Arlo a sense of purpose, Henry puts him in charge of guarding their silo from critters and helping him set up a trap. While Libby and Buck easily adjust to life and their chores on their farm and make their mark (signified by a mud-print on a corn silo), Arlo's timid nature makes his tasks difficult for him. Millions of years later, two Apatosaurus named Henry (Jeffrey Wright) and Ida (Frances McDormand), who are farmers, give birth to three children: Libby (Maleah Padilla), Buck (Marcus Scribner), and the runt Arlo (Raymond Ochoa). In an alternate time-line, the asteroid that would have caused the extinction of dinosaurs 65 million years ago passes safely over Earth.

Arlo good dinosaur sketch