The Earliest fish appeared in the Cambrian as small filter feeders; they ongoing to evolve through the Paleozoic, diversifying into a lot of varieties. The earliest fish with focused respiratory gills and paired fins, the ostracoderms, experienced hefty bony plates that served as protective exoskeletons in opposition to invertebrate predators. https://maps.app.goo.gl/kTisAZCbSjAw6nkX8