Devonian

Devonian
419.2 ± 3.2 – 358.9 ± 0.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Late Devonian world map
Chronology
−420 — – −415 — – −410 — – −405 — – −400 — – −395 — – −390 — – −385 — – −380 — – −375 — – −370 — – −365 — – −360 — – Paleozoic Silurian Devonian Carboniferous Early Mid Late Lochkovian Pragian Emsian Eifelian Givetian Frasnian Famennian           ← Rhynie chert[1] ← Hangenberg event, Famennian glaciation ← Kellwasser event (Late Devonian extinction)[2] ← Widespread[3] shrubs & trees ← Hunsrück fauna Subdivision of the Devonian according to the ICS, as of 2021.[4] Vertical axis scale: millions of years ago.
Etymology
Name formality	Formal
Nickname(s)	Age of Fishes
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Period
Stratigraphic unit	System
Time span formality	Formal
Lower boundary definition	FAD of the Graptolite Monograptus uniformis
Lower boundary GSSP	Klonk, Czech Republic 49°51′18″N 13°47′31″E / 49.8550°N 13.7920°E / 49.8550; 13.7920
Lower GSSP ratified	1972[5]
Upper boundary definition	FAD of the Conodont Siphonodella sulcata (discovered to have biostratigraphic issues as of 2006).[6]
Upper boundary GSSP	La Serre, Montagne Noire, France 43°33′20″N 3°21′26″E / 43.5555°N 3.3573°E / 43.5555; 3.3573
Upper GSSP ratified	1990[7]
Atmospheric and climatic data
Sea level above present day	Relatively steady around 189 m, gradually falling to 120 m through period[8]

The Devonian (/dɪˈvoʊni.ən, dɛ-/ də-VOH-nee-ən, de-)^[9][10] is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya.^[11] It is named after Devon, England, where rocks from this period were first studied.

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. The arthropod groups of myriapods, arachnids and hexapods also became well-established early in this period, after starting their expansion to land at least from the Ordovician period.

Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. The placoderms began dominating almost every known aquatic environment. The ancestors of all four-limbed vertebrates (tetrapods) began adapting to walk on land, as their strong pectoral and pelvic fins gradually evolved into legs, though they were not fully established until the Late Carboniferous.^[12] In the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician.

The first ammonites, a subclass 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^[13] severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida.

Devonian palaeogeography was dominated by the supercontinent of Gondwana to the south, the small continent of Siberia to the north, and the medium-sized continent of Laurussia to the east. Major tectonic events include the closure of the Rheic Ocean, the separation of South China from Gondwana, and the resulting expansion of the Paleo-Tethys Ocean. The Devonian experienced several major mountain-building events as Laurussia and Gondwana approached; these include the Acadian Orogeny in North America and the beginning of the Variscan Orogeny in Europe. These early collisions preceded the formation of Pangaea in the Late Paleozoic.