The first true corals appeared during the Cambrian period, roughly 540 – 485 million years ago. That is before the appearance of the dinosaurs, fish, land plants, and even the Appalachian Mountains! Some “modern” species appeared slightly more recently, during the middle Triassic period, which is around the time that the first dinosaurs walked the Earth. And the ancestors of corals are even older — their fossil records extend back 550 million years!