Early Devonian

EtymologyChronostratigraphic nameLower DevonianGeochronological nameEarly DevonianName formalityFormalUsage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitEpochStratigraphic unitSeriesTime span formalityFormalLower boundary definitionFAD of the graptoliteMonograptus uniformisLower boundary GSSPKlonk, Czech Republic
49°51′18″N13°47′31″E / 49.8550°N 13.7920°E / 49.8550; 13.7920Lower GSSP ratified1972Upper boundary definitionFAD of the conodontPolygnathus costatus partitusUpper boundary GSSP, , Eifel, Germany
50°08′59″N6°28′18″E / 50.1496°N 6.4716°E / 50.1496; 6.4716Upper GSSP ratified1985

The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonianseries. It lasted from 419.62 ± 1.36 to 393.47 ± 0.99 and began with the Lochkovian Stage 419.62 ± 1.36 to 413.02 ± 0.99, which was followed by the Pragian from 413.02 ± 1.36 to 410.62 ± 0.99 and then by the Emsian, which lasted until the Middle Devonian began, 393.47± 0.99 million years ago. During this time, the first ammonoids appeared, descending from bactritoidnautiloids. Ammonoids during this time period were simple and differed little from their nautiloid counterparts. These ammonoids belong to the order Agoniatitida, which in later epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida. This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic Era.