<P> The evolution of fish began about 530 million years ago during the Cambrian explosion . It was during this time that the early chordates developed the skull and the vertebral column , leading to the first craniates and vertebrates . The first fish lineages belong to the Agnatha , or jawless fish . Early examples include Haikouichthys . During the late Cambrian , eel - like jawless fish called the conodonts , and small mostly armoured fish known as ostracoderms , first appeared . Most jawless fish are now extinct ; but the extant lampreys may approximate ancient pre-jawed fish . Lampreys belong to the Cyclostomata , which includes the extant hagfish , and this group may have split early on from other agnathans . </P>
<P> The evolution of fish began about 530 million years ago during the Cambrian explosion . It was during this time that the early chordates developed the skull and the vertebral column , leading to the first craniates and vertebrates . The first fish lineages belong to the Agnatha , or jawless fish . Early examples include Haikouichthys . During the late Cambrian , eel - like jawless fish called the conodonts , and small mostly armoured fish known as ostracoderms , first appeared . Most jawless fish are now extinct ; but the extant lampreys may approximate ancient pre-jawed fish . Lampreys belong to the Cyclostomata , which includes the extant hagfish , and this group may have split early on from other agnathans . </P>
fish appeared in the fossil record during the
fish appeared in the fossil record during the
the Cambrian explosion
the Cambrian explosion