Early Devonian

Early Devonian
419.2 ± 3.2 – 393.3 ± 0.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Map of Earth as it appeared 400 million years ago during the early Devonian, Emsian stage[citation needed]
Sample from the Lower Devonian Rhynie chert
Chronology
−420 — – −415 — – −410 — – −405 — – −400 — – −395 — – −390 — – −385 — – −380 — – −375 — – −370 — – −365 — – −360 — – Paleozoic S Devonian C Mississippian Přídolí Early Mid Late Early M 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
Chronostratigraphic name	Lower Devonian
Geochronological name	Early Devonian
Name formality	Formal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Epoch
Stratigraphic unit	Series
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 Polygnathus costatus partitus
Upper boundary GSSP	Wetteldorf Richtschnitt section, Wetteldorf, Eifel, Germany 50°08′59″N 6°28′18″E / 50.1496°N 6.4716°E / 50.1496; 6.4716
Upper GSSP ratified	1985[6]

The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from 419.2 ± 3.2 to 393.3 ± 1.2 and began with the Lochkovian Stage 419.2 ± 3.2 to 410.8 ± 1.2, which was followed by the Pragian from 410.8 ± 3.2 to 407.6 ± 1.2 and then by the Emsian, which lasted until the Middle Devonian began, 393.3± 1.2 million years ago.^[7] During this time, the first ammonoids appeared, descending from bactritoid nautiloids. 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.