<P> The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya . It is named after Devon, England, where rocks from this period were first studied . </P> <P> The first significant adaptive radiation of life on dry land occurred during the Devonian . Free - sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents . By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed - bearing plants appeared . Various terrestrial arthropods also became well - established . </P> <P> Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the "Age of Fish". The first ray - finned and lobe - finned bony fish appeared, while the placoderms began dominating almost every known aquatic environment . The ancestors of all four - limbed vertebrates (tetrapods) began adapting to walking on land, as their strong pectoral and pelvic fins gradually evolved into legs . In the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician . </P> <P> The first ammonites, species of molluscs, appeared . Trilobites, the mollusc - like brachiopods and the great coral reefs, were still common . The Late Devonian extinction which started about 375 million years ago severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida . </P>

Which period is known as the age of the fishes