Middle Devonian
Chronology
Etymology
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitEpoch
Stratigraphic unitSeries
Time span formalityFormal
Lower boundary definitionFad of the Conodont Polygnathus costatus partitus
Lower boundary GSSPWetteldorf Richtschnitt, Eifel hills, Germany
50°08′59″N 6°28′18″E / 50.1496°N 6.4716°E / 50.1496; 6.4716
Lower GSSP ratified1985
Upper boundary definitionFAD of the Conodont Ancyrodella rotundibola
Upper boundary GSSPCol du Puech de la Suque, Montagne Noire, France
43°30′12″N 3°05′12″E / 43.5032°N 3.0868°E / 43.5032; 3.0868
Upper GSSP ratified1986

In the geological timescale, the Middle Devonian epoch (from 397.5 ± 2.7 million years ago to 385.3 ± 2.6 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.

References

  1. ↑ 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. London: Geological Society. 168 (4): 863–872. doi:10.1144/0016-76492010-043.
  2. ↑ 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.
  3. ↑ 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.
  4. ↑ "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
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