Vertebrates - Fish

The earliest group of fish to be found as fossils are classified as agnathans. In Wyoming, USA, small pieces of bone from these fish are earliest vertebrate remains in rocks of Cambrian age. Agnathans are a group with jaws, and many had thin, heavily armoured bodies. The ostracoderms are the main fossil representatives within the agnathan class, which today contains the scale-less, eel-like lampreys (sometimes also called lamprey eels)

During the Late Silurian and Devonian periods fish evolved rapidly. With a number groups developed. The Placoderms, which are now extinct, had primitive jaws and paired fins. These fish were the most common vertebrates towards the end of the Devonian period. Other jawed fish include the Chondrichthyes. Some fish within this group have skeletons made of cartilage, and sharks such as Carcharodon are classified here. The final important group are the Osteichthyes. These are the bony fish common and wide-spread today, which first appear as fossils in the Devonian period. Within this group the teleosts are the most numerous, and the Crossopterygians have many similarities with Amphibians.