Tetracods are future descendants of Atlantic cods that survived the Holocene extinction and having their populations recovered. They evolved from a group of Atlantic cods that crawled onto land as alligator-sized omnivorous mudskipper-like fish with lungs and vocal cords (which caused them to have crocodile-like sounds), but after the mass extinction in 500 million years A.D. some have survived extinction and diversified to replaced the extinct mammals and birds. They rule earth from 510 million years A.D. to 1 billion years A.D, about 490 million years, making them the most successful creatures on earth, more so than the prehistoric dinosaurs, which ruled only for about 170 million years. They rule on the supercontinent called Pangaea II, which consists all continents during the Tetracod's reign. Tetracods come in many different variety of forms, ranging from lizard-like species to gigantic placerias-like species.