It is thought that teeth evolved twice throughout history. At first, scientists thought that teeth only evolved once due to their highly organized structure but evidence from fossil placoderms proves otherwise. Teeth are first found in the armored fishes, or placoderms that lived 408 million years ago. These fish were the first to have jaws and caught their dinner using teeth-like blades made out of semidentine. Teeth evolved once when a relative of these fishes adapted a better way to catch their prey, leading to the evolution of sharks and bony fishes. Another evolution of teeth may have occurred with a more advanced placoderm. Fossil teeth from the placoderm known as Arthrodira, have been found to be conical and formed into rows. These fossil teeth were also made out of dentine, not semidentine, indicating another origin for the evolution of teeth. Other jawed vertebrates could have also adapted to catching their prey more efficiently by developing teeth and whether there are many more origins for teeth is unknown at this point.