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TheEarly Devonian is the first of threeepochs comprising theDevonian period, corresponding to theLower Devonianseries. It lasted from419.62 ± 1.36 to393.47 ± 0.99 and began with theLochkovian Stage419.62 ± 1.36 to413.02 ± 0.99, which was followed by thePragian from413.02 ± 1.36 to410.62 ± 0.99 and then by theEmsian, which lasted until theMiddle Devonian began,393.47± 0.99 million years ago.^[7]During this time, the firstammonoids appeared, descending frombactritoid nautiloids. Ammonoids during this time period were simple and differed little from their nautiloid counterparts. These ammonoids belong to the orderAgoniatitida, which in later epochs evolved to new ammonoid orders, for exampleGoniatitida andClymeniida. This class ofcephalopod molluscs would dominate the marine fauna until the beginning of theMesozoic Era.

References

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^Kaufmann, Bernd; Trapp, Endres; Mezger, Klaus (2004). "The numerical age of the Upper Frasnian (Upper Devonian) Kellwasser horizons: A new U-Pb zircon date from Steinbruch Schmidt(Kellerwald, Germany)".The Journal of Geology.112 (4):495–501.Bibcode:2004JG....112..495K.doi:10.1086/421077.
^Algeo, Thomas (1998). "Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events".Philosophical Transactions of the Royal Society B: Biological Sciences.353 (1365):113–130.doi:10.1098/rstb.1998.0195.
^Parry, Stephen; Noble, Stephen; Crowley, Quentin; Wellman, Charles (2011)."A high-precision U–Pb age constraint on the Rhynie Chert Konservat-Lagerstätte: time scale and other implications".Journal of the Geological Society.168 (4). London: Geological Society:863–872.doi:10.1144/0016-76492010-043.
^"International Chronostratigraphic Chart"(PDF).International Commission on Stratigraphy. September 2023. RetrievedOctober 23, 2025.
^Chlupáč, Ivo; Hladil, Jindrich (January 2000)."The global stratotype section and point of the Silurian-Devonian boundary".CFS Courier Forschungsinstitut Senckenberg:1–8. Retrieved7 December 2020.
^Ziegler, W.; Klapper, G. (June 1985)."Stages of the Devonian System"(PDF).Episodes.8 (2):104–109.doi:10.18814/epiiugs/1985/v8i2/006. Retrieved18 December 2020.
^Cohen, K.M.; Finney, S.C.; Gibbard, P.L.; Fan, J.-X. (2013)."The ICS International Chronostratigraphic Chart"(PDF).Episodes.36 (3):199–204.doi:10.18814/epiiugs/2013/v36i3/002. Retrieved7 January 2021.

Geological history of Earth

Cenozoic Era
(present–66.0 Ma)

Quaternary(present–2.58 Ma)	Holocene (present–11.7 ka) Pleistocene (11.7 ka–2.58 Ma)
Neogene(2.58–23.0 Ma)	Pliocene (2.59–5.33 Ma) Miocene (5.33–23.0 Ma)
Paleogene(23.0–66.0 Ma)	Oligocene (23.0–33.9 Ma) Eocene (33.9–56.0 Ma) Paleocene (56.0–66.0 Ma)

Mesozoic Era
(66.0–252 Ma)

Cretaceous(66.0–145 Ma)	Late (66.0–100 Ma) Early (100–145 Ma)
Jurassic(145–201 Ma)	Late (145–164 Ma) Middle (164–174 Ma) Early (174–201 Ma)
Triassic(201–252 Ma)	Late (201–237 Ma) Middle (237–247 Ma) Early (247–252 Ma)

Paleozoic Era
(252–539 Ma)

Permian(252–299 Ma)	Lopingian (252–260 Ma) Guadalupian (260–272 Ma) Cisuralian (272–299 Ma)
Carboniferous(299–359 Ma)	Pennsylvanian (299–323 Ma) Mississippian (323–359 Ma)
Devonian(359–419 Ma)	Late (359–383 Ma) Middle (383–393 Ma) Early (393–419 Ma)
Silurian(419–444 Ma)	Pridoli (419–423 Ma) Ludlow (423–427 Ma) Wenlock (427–433 Ma) Llandovery (433–444 Ma)
Ordovician(444–485 Ma)	Late (444–458 Ma) Middle (458–470 Ma) Early (470–485 Ma)
Cambrian(485–539 Ma)	Furongian (485–497 Ma) Miaolingian (497–509 Ma) Series 2 (509–521 Ma) Terreneuvian (521–539 Ma)

Proterozoic Eon
(539 Ma–2.5 Ga)

Neoproterozoic(539 Ma–1 Ga)	Ediacaran (539–635 Ma) Cryogenian (635–720 Ma) Tonian (720 Ma–1 Ga)
Mesoproterozoic(1–1.6 Ga)	Stenian (1–1.2 Ga) Ectasian (1.2–1.4 Ga) Calymmian (1.4–1.6 Ga)
Paleoproterozoic(1.6–2.5 Ga)	Statherian (1.6–1.8 Ga) Orosirian (1.8–2.05 Ga) Rhyacian (2.05–2.3 Ga) Siderian (2.3–2.5 Ga)