The Earliest fish appeared through the Cambrian as smaller filter feeders; they ongoing to evolve with the Paleozoic, diversifying into a lot of sorts. The earliest fish with devoted respiratory gills and paired fins, the ostracoderms, experienced hefty bony plates that served as protective exoskeletons versus invertebrate predators. Encyclopaedia Britannica's https://maps.app.goo.gl/kTisAZCbSjAw6nkX8