Carboniferous

The second episode shows the swampy coal forests of the Carboniferous. It explains that because of a much higher oxygen content in the atmosphere, giant landarthropods evolved, such as a Mesothelae (a member of the primitive spider suborder however this one is the first species of that order), Meganeura; a giant dragonfly the size of a eagle and Arthropleura; a huge millipede relative. A Mesothelae hunts down a Petrolacosaurus. She comes back from her hunting expedition only to find herburrow has flooded. Not only that, the Petrolacosaurus she caught is stolen by aMeganeura. On the spider's search for a new burrow, she passes a pond full of Reptiliomorphs (which would make a more central appearance later on). Later she is chased by an Arthropleura, which is later killed in a fight with a Proterogyrinus. The Mesothelae finally chases a Petrolacosaurus out of its own burrow and moves in. A storm brews and the narrator explains that its high oxygen content makes the atmosphere very combustible, so lightning is a real danger. The Proterogyrinus are seen leaping out of the water to catch Meganeura, which were driven below the tree canopy by the storm. Later, lightning and a forest fire pour in, devastating the life around. At last, only some animals survive...including Petrolacosaurus, who finds the dead body of the Mesothelae (her burrow was at the centre of a lightning strike) and begins to feed upon the spider's carcass.

Animals: Megarachne  · Petrolacosaurus  · Meganeura  · Arthropleura  ·Proterogyrinus  , Crassigyrinus