Middle Devonian

Middle Devonian
393.3 ± 1.2 – 382.7 ± 1.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N
A map of Earth as it appeared 390 million years ago during the Middle Devonian Epoch, Eifelian Age
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           ← Hangenberg event, Famennian glaciation ← Kellwasser event (Late Devonian extinction)[1] ← Widespread[2] shrubs & trees ← Hunsrück fauna ← Rhynie chert[3] Subdivision of the Devonian according to the ICS, as of 2023.[4] Vertical axis scale: Millions of years ago
Etymology
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 Conodont Polygnathus costatus partitus
Lower boundary GSSP	Wetteldorf Richtschnitt, Eifel hills, Germany 50.1496°N 6.4716°E / 50.1496; 6.4716
Lower GSSP ratified	1985
Upper boundary definition	FAD of the Conodont Ancyrodella rotundibola
Upper boundary GSSP	Col du Puech de la Suque, Montagne Noire, France 43.5032°N 3.0868°E / 43.5032; 3.0868
Upper GSSP ratified	1986

In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age.

The Middle Devonian epoch is subdivided into two stages: Eifelian and Givetian.

Life in the Middle Devonian

In the middle Devonian the armored jawless fish known as ostracoderms were declining in diversity and instead the jawed fish were thriving and increasing in diversity in both the oceans and freshwater. The shallow, warm, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop essential characteristics such as well developed lungs, ability to crawl out of the water and onto the land for short periods of time, possibly in search of food which would be developed by the tetrapods later in the Late Devonian which are descendents of these early fish.

The earliest forest grew in the Middle Devonian (Eifelian) time. This new environment was formed by cladoxylopsid trees including Calamophyton.^[5]

The Taghanic event took place near the end of the Middle Devonian.

References

1. Kaufmann, B.; Trapp, E.; Mezger, K. (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.
2. Algeo, T. J. (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.
3. Parry, S. F.; Noble, S. R.; Crowley, Q. G.; Wellman, C. H. (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.
4. "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. September 2023. Retrieved December 16, 2024.
5. Davies, Neil S., McMahon, William J. and Berry, Christopher M. (2024). "Earth's earliest forest: fossilized trees and vegetation-induced sedimentary structures from the Middle Devonian (Eifelian) Hangman Sandstone Formation, Somerset and Devon, SW England" (PDF). Journal of the Geological Society. doi:10.1144/jgs2023-204. Archived (PDF) from the original on 2024-03-09.