Brontoscorpio (meaning, "Thunder Scorpion") is an armoured arthropod of the Silurian Period, a Eurypterid - a "sea scorpion". It is known thought this creature hunted ancient fish and other smaller sea creatures. Larger predators in the waters in which it lived, would have in turn preyed on Brontoscorpio - including Giant Orthocones, and even sea scorpions larger than Brontoscorpio, especially Pterygotus.
In Episode 1, a Brontoscorpio tries to go after a Cephalaspis, but it was caught by a Pterygotus and was fed to her young. All the Cephalasphis go to the other side of the ocean and a group of Brontoscorpios grab and kill some of the Cepalasphis and eat them. One Brontoscorpio missed his chance after he shed his skin and then walks back to the ocean.