The Earliest fish appeared in the course of the Cambrian as small filter feeders; they continued to evolve in the Paleozoic, diversifying into lots of types. The earliest fish with dedicated respiratory gills and paired fins, the ostracoderms, experienced major bony plates that served as protective exoskeletons against invertebrate predators. https://maps.app.goo.gl/kTisAZCbSjAw6nkX8