Dévonien

The Dévonien, also known as the Devonian period, is a geological period and system that spans from approximately 419.2 million to 358.9 million years ago, during the Paleozoic era. It is named after Devon, England, where rock formations from this period were first studied. The Devonian period is often referred to as the "Age of Fishes" due to the proliferation and diversification of vertebrate life in the oceans during this time.

The Devonian period is divided into four epochs: the Pragian, Emsian, Eifelian, Givetian, Frasnian, and Famennian, with the first three sometimes grouped as the Early Devonian and the last three as the Late Devonian. This period followed the Silurian and was succeeded by the Carboniferous period.

During the Devonian, the supercontinent Gondwana began to drift toward the equator, while the northern continent, Laurussia (comprising Laurentia, Baltica, and Avalonia), collided with it to form Pangaea. These movements led to the formation of extensive shallow seas, which fostered diverse marine ecosystems. The oceans were home to early jawed fishes, such as placoderms and acanthodians, as well as the first true bony fishes and cartilaginous fishes. The Devonian also saw the rise of the first tetrapods, which were amphibian-like vertebrates that eventually colonized land.

On land, plants continued to diversify, with vascular plants such as ferns, horsetails, and early seed plants becoming more widespread. Insects also evolved during this period, with the first winged insects appearing in the late Devonian. The end of the Devonian period was marked by the Hangenberg event, a mass extinction that significantly reduced marine biodiversity and paved the way for the Carboniferous period.

The Devonian period is notable for its rich fossil record, particularly in marine environments, which provides valuable insights into the evolution of early vertebrates and the development of complex ecosystems.