The jawed fish that are still extant in modern days also appeared during the late Silurian: the Chondrichthyes (or cartilaginous fish) and the Osteichthyes (or bony fish). They are first represented in the fossil record from the Silurian by two groups of fish: the armoured fish known as placoderms, which evolved from the ostracoderms and the Acanthodii (or spiny sharks). The earliest jawed vertebrates probably developed during the late Ordovician period. Lampreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans. Most jawless fish are now extinct but the extant lampreys may approximate ancient pre-jawed fish. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. The first fish lineages belong to the Agnatha, or jawless fish. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The evolution of fish began about 530 million years ago during the Cambrian explosion. The Devonian period 419–359 Ma (Age of Fishes) saw the development of early sharks, armoured placoderms and various lobe-finned fishes including the tetrapod transitional species Origin and diversification of fish through geologic time
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