Pterygotus was one of the largest arthropods that ever lived. Pterygotus was part of a group of arthropod called eurypterids. There were many species of eurypterids. They first appeared in the Ordovician and died out in the Permian. Pterygotus appeared in the Silurian and died out in the Devonian. Pterygotus could grow to a length of 7 feet long. Pterygotus had large compound eyes, suggesting Pterygotus had sharp eyesight. Paleontologists believe Pterygotus hid in the sand while it waited for prey. When prey came, Pterygotus would then grab it and tear its prey apart.