The Devonian, part of the Paleozoic era, is otherwise known as the Age of ... later gave rise to sharks and rays. They had small, rough scales, fixed fins, and sharp, replaceable teeth.

The Paleozoic era's Silurian period saw animals and plants ... A group called acanthodians, or spiny sharks, evolved more menacing mouths with jaws. While these fish, the first true jawed fish ...