A short sequence depicts Cephalaspis evolving into Hynerpeton, amphibian-like tetrapods, who now hunt their arthropod contemporaries which have shrunk. Though capable of terrestrial movement, Hynerpeton have to remain near water to keep moist and reproduce. A lone male Hynerpeton hunting underwater is threatened by predatory fish, at first by a Stethacanthus which is eaten by a two-ton Hyneria that chases the amphibian out of the water. After seeing off a rival during the night, the male finds a receptive female at dawn and the two mate at the water's edge. They are ambushed by the Hyneria, which beaches itself in the attack, but then uses its fins to drag itself ashore and grab the fleeing male. Despite his untimely death, the Hynerpeton eggs were successfully fertilised and sink into the water to develop. A sequence depicts them acquiring hard shells as the first reptiles evolve, but as the offspring leave their nest, those still hatching are left at the mercy of a giant spider, foreshadowing the return of the arthropods.