The Silurian and Devonian Periods are divisions of the Paleozoic Era. The Silurian Period, 438 to 408 million years ago, is characterized by the appearance of large coral reefs and the diversification of fish species. Life, in the form of primitive plants and insects, made the first brave advances to existence on land. The Silurian was followed by the Devonian Period, from 408 to 360 million years ago. During the Devonian, land plants grew into the first forests, and the first vertebrate animals colonized the land. At this time, North America was attached to Europe in a large landmass situated at the equator.
Silurian and Devonian features of the United States: