View source for Late Devonian mass extinction

{{Short description|Second of the big five mass extinctions}}
{{annotated image/Extinction|caption=Comparison of the three episodes of extinction in the Late Devonian (Late D) to other mass extinction events in [[History of Earth|Earth's history]]. Plotted is the extinction intensity, calculated from marine [[genus|genera]].}}

The '''Late Devonian mass extinction''', also known as the '''Kellwasser event''', was a [[Extinction event|mass extinction event]] which occurred around 372 million years ago, at the boundary between the [[Frasnian]] and [[Famennian]] ages of the [[Late Devonian]] period.<ref name=":0">{{cite journal |last1=Becker |first1=R. Thomas |last2=House |first2=Michael R. |date=13 March 1986 |title=Kellwasser Events and goniatite successions in the Devonian of the Montagne Noire with comments on possible causations |url=https://www.researchgate.net/publication/262715543 |journal=[[Courier Forschungsinstitut Senckenberg]] |volume=169 |pages=45–77 |access-date=19 April 2023}}</ref><ref name="Racki, 2005">Racki, 2005</ref><ref name="McGhee">McGhee, George R. Jr, 1996. The Late Devonian Mass Extinction: the Frasnian/Famennian Crisis (Columbia University Press) {{ISBN|0-231-07504-9}}</ref> It is placed as one of the "Big Five" most severe mass extinction events in Earth's history,<ref>{{Cite book |last=McGhee |first=George R. |url=https://onlinelibrary.wiley.com/doi/book/10.1002/047001590X |title=Encyclopedia of Life Sciences |date=2005-09-09 |publisher=Wiley |isbn=978-0-470-01617-6 |edition=1 |language=en |chapter=Extinction: Late Devonian Mass Extinction |doi=10.1002/9780470015902.a0001653.pub3}}</ref> with likely around 40% of marine species going extinct, though the degree of severity is contested.<ref>{{Cite journal |last=Stanley |first=Steven M. |date=18 October 2016 |title=Estimates of the magnitudes of major marine mass extinctions in earth history |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |language=en |volume=113 |issue=42 |pages=E6325–E6334 |bibcode=2016PNAS..113E6325S |doi=10.1073/pnas.1613094113 |issn=0027-8424 |pmc=5081622 |pmid=27698119 |doi-access=free}}</ref> A second mass extinction called the [[Hangenberg event]], also known as the end-Devonian extinction,<ref name="Sallan2015">{{cite journal |last1=Sallan |first1=L. |last2=Galimberti |first2=A. K. |date=2015-11-13 |title=Body-size reduction in vertebrates following the end-Devonian mass extinction |journal=Science |volume=350 |issue=6262 |pages=812–815 |doi=10.1126/science.aac7373 |pmid=26564854 |bibcode=2015Sci...350..812S |s2cid=206640186}}</ref> occurred 13 million years later around 359 million years ago, bringing an end to the Famennian and Devonian, as the world transitioned into the [[Carboniferous|Carboniferous Period]].<ref>{{cite journal |last1=Caplan |first1=Mark L |last2=Bustin |first2=R.Mark |title=Devonian–Carboniferous Hangenberg mass extinction event, widespread organic-rich mudrock and anoxia: causes and consequences |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |date=May 1999 |volume=148 |issue=4 |pages=187–207 |doi=10.1016/S0031-0182(98)00218-1 |bibcode=1999PPP...148..187C |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018298002181|url-access=subscription }}</ref> The effects of the two extinction events have historically been conflated, and both events collectively profoundly reshaped marine ecosystems.<ref>{{Cite journal |last=Marshall |first=Charles R. |date=2023 |title=Forty years later: The status of the "Big Five" mass extinctions |journal=Cambridge Prisms: Extinction |language=en |volume=1 |article-number=e5 |doi=10.1017/ext.2022.4 |issn=2755-0958 |pmc=11895713 |pmid=40078681}}</ref>

Although it is well established that there was a massive [[loss of biodiversity]] in the Late Devonian, the timespan of this event is uncertain, with estimates ranging from 500,000 to 25 million years, extending from the mid-Givetian to the end-Famennian.<ref>{{Cite web|last=Stigall|first=Alycia|date=2011|title=GSA Today - Speciation collapse and invasive species dynamics during the Late Devonian "Mass Extinction"|url=https://www.geosociety.org/gsatoday/archive/22/1/article/i1052-5173-22-1-4.htm|access-date=2021-03-30|website=www.geosociety.org}}</ref> Some consider the extinction to be as many as seven distinct events, spread over about 25 million years, with notable extinctions at the ends of the [[Givetian]], [[Frasnian]], and [[Famennian]] ages.<ref name="sole">Sole, R. V., and Newman, M., 2002. "Extinctions and Biodiversity in the Fossil Record - Volume Two, The earth system: biological and ecological dimensions of global environment change" pp. 297-391, ''Encyclopedia of Global Environmental Change'' John Wiley & Sons.</ref>

By the Late Devonian, the land had been colonized by [[plants]] and [[insects]]. In the oceans, massive [[reef]]s were built by corals and [[Stromatoporoidea|stromatoporoids]]. [[Euramerica]] and [[Gondwana]] were beginning to converge into what would become [[Pangaea]]. The extinction seems to have only affected [[marine life]]. Hard-hit groups include [[brachiopod]]s, [[trilobite]]s, and reef-building [[organism]]s; the last almost completely disappeared. The causes of these extinctions are unclear. Leading hypotheses include changes in sea level and ocean [[anoxic event|anoxia]], possibly triggered by [[global cooling]] or oceanic volcanism. The impact of a [[comet]] or another extraterrestrial body has also been suggested,<ref>Sole, R. V., and Newman, M. [http://www.santafe.edu/media/workingpapers/99-12-079.pdf Patterns of extinction and biodiversity in the fossil record] {{Webarchive|url=https://web.archive.org/web/20120314144008/http://www.santafe.edu/media/workingpapers/99-12-079.pdf |date=2012-03-14 }}</ref> such as the [[Siljan Ring]] event in Sweden. Some statistical analysis suggests that the decrease in diversity was caused more by a decrease in [[speciation]] than by an increase in extinctions.<ref>{{Cite journal | last1=Bambach | first1=R.K. | last2=Knoll | first2=A.H. | last3=Wang | first3=S.C. | title=Origination, extinction, and mass depletions of marine diversity | journal=[[Paleobiology (journal)|Paleobiology]] | volume=30 | issue=4 | pages=522–542 | date=December 2004 | url=http://www.bioone.org/perlserv/?request=get-document&issn=0094-8373&volume=30&page=522 | doi=10.1666/0094-8373(2004)030<0522:OEAMDO>2.0.CO;2  | bibcode=2004Pbio...30..522B | s2cid=17279135 | url-access=subscription }}</ref><ref name="Stigall, 2011">Stigall, 2011</ref> This might have been caused by invasions{{from where?|date=September 2025}} of cosmopolitan species, rather than by any single event.<ref name="Stigall, 2011" /> [[Placodermi|Placoderms]] were hit hard by the Kellwasser event and completely died out in the Hangenberg event, but most other jawed vertebrates were less strongly impacted. [[Agnatha]]ns (jawless fish) were in decline long before the end of the Frasnian and were nearly wiped out by the extinctions.<ref name="Sallan and Coates, 2010">{{cite journal |last1=Sallan |first1=L. C. |last2=Coates |first2=M. I. |title=End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates |journal=Proceedings of the National Academy of Sciences |date=June 2010 |volume=107 |issue=22 |pages=10131–10135 |doi=10.1073/pnas.0914000107|pmid=20479258 |pmc=2890420 |bibcode=2010PNAS..10710131S |doi-access=free }}</ref>

The extinction event was accompanied by widespread oceanic [[anoxic event|anoxia]]; that is, a lack of oxygen, prohibiting decay and allowing the preservation of organic matter.<ref>{{cite journal |last1=Girard |first1=Catherine |last2=Renaud |first2=Sabrina |date=25 June 2007 |title=Quantitative conodont-based approaches for correlation of the Late Devonian Kellwasser anoxic events |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018207001514 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=250 |issue=1–4 |pages=114–125 |doi=10.1016/j.palaeo.2007.03.007 |bibcode=2007PPP...250..114G |access-date=15 January 2023|url-access=subscription }}</ref><ref name="CarmichaelEtAl2019">{{cite journal |last1=Carmichael |first1=Sarah K. |last2=Waters |first2=Johnny A. |last3=Königshof |first3=Peter |last4=Suttner |first4=Thomas J. |last5=Kido |first5=Erika |date=December 2019 |title=Paleogeography and paleoenvironments of the Late Devonian Kellwasser event: A review of its sedimentological and geochemical expression |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818118306258 |journal=[[Global and Planetary Change]] |volume=183 |article-number=102984 |doi=10.1016/j.gloplacha.2019.102984 |bibcode=2019GPC...18302984C |s2cid=198415606 |access-date=23 December 2022|url-access=subscription }}</ref> This, combined with the ability of porous reef rocks to hold oil, has led to Devonian rocks being an important source of oil, especially in [[Canada]] and the [[United States]].<ref>{{cite journal |last1=Wang |first1=Pengwei |last2=Chen |first2=Zhuoheng |last3=Jin |first3=Zhijun |last4=Jiang |first4=Chunqing |last5=Sun |first5=Mingliang |last6=Guo |first6=Yingchun |last7=Chen |first7=Xiao |last8=Jia |first8=Zekai |date=February 2018 |title=Shale oil and gas resources in organic pores of the Devonian Duvernay Shale, Western Canada Sedimentary Basin based on petroleum system modeling |url=https://www.sciencedirect.com/science/article/abs/pii/S1875510017304584 |journal=Journal of Natural Gas Science and Engineering |volume=50 |pages=33–42 |doi=10.1016/j.jngse.2017.10.027 |bibcode=2018JNGSE..50...33W |access-date=15 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Dong |first1=Tian |last2=Harris |first2=Nicholas B. |last3=McMillan |first3=Julia M. |last4=Twemlow |first4=Cory E. |last5=Nassichuk |first5=Brent R. |last6=Bish |first6=David L. |date=15 May 2019 |title=A model for porosity evolution in shale reservoirs: An example from the Upper Devonian Duvernay Formation, Western Canada Sedimentary Basin |url=https://pubs.geoscienceworld.org/aapgbull/article/103/5/1017/569910/A-model-for-porosity-evolution-in-shale-reservoirs |journal=[[AAPG Bulletin]] |volume=103 |issue=5 |pages=1017–1044 |doi=10.1306/10261817272 |bibcode=2019BAAPG.103.1017D |s2cid=135341837 |access-date=15 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Smith |first1=Mark G. |last2=Bustin |first2=R. Marc |date=1 July 2000 |title=Late Devonian and Early Mississippian Bakken and Exshaw Black Shale Source Rocks, Western Canada Sedimentary Basin: A Sequence Stratigraphic Interpretation |url=https://pubs.geoscienceworld.org/aapgbull/article/84/7/940/39815/Late-Devonian-and-Early-Mississippian-Bakken-and |journal=[[AAPG Bulletin]] |volume=84 |issue=7 |pages=940–960 |doi=10.1306/A9673B76-1738-11D7-8645000102C1865D |access-date=15 January 2023|url-access=subscription }}</ref>

==Late Devonian world==
{{Devonian graphical timeline}}
During the Late Devonian, the continents were arranged differently from today, with a supercontinent, [[Gondwana]], covering much of the Southern Hemisphere. The [[continent]] of [[Siberia (continent)|Siberia]] occupied the Northern Hemisphere, while an equatorial continent, [[Laurussia]] (formed by the collision of [[Baltica]] and [[Laurentia]]), was [[continental drift|drifting]] towards Gondwana, closing the [[Rheic Ocean]]. The [[Caledonian orogeny|Caledonian Mountains]] were also growing across what is now the [[Scottish Highlands]] and [[Scandinavia]], while the [[Appalachians]] rose over America.<ref name="McKerrow">{{cite journal |last1=McKerrow |first1=W.S. |last2=Mac Niocaill |first2=C. |last3=Dewey |first3=J.F. |date=2000 |title=The Caledonian Orogeny redefined |journal=Journal of the Geological Society |volume=157 |issue=6 |pages=1149–1154 |doi=10.1144/jgs.157.6.1149 |bibcode=2000JGSoc.157.1149M |s2cid=53608809 |url=https://ora.ox.ac.uk/objects/uuid:023c19c1-20dc-4af2-8a8d-32edd0005c22 }}</ref>

The biota was also very different. Plants, which had been on land in forms similar to mosses and liverworts since the [[Ordovician]], had just developed roots, seeds, and [[Blood vessel|water transport]] systems that allowed them to survive away from places that were constantly wet—and so grew huge forests on the highlands. Several clades had developed a shrubby or tree-like habit by the Late Givetian, including the [[Cladoxylopsid|cladoxylalean]] [[fern]]s, [[lepidodendrales|lepidosigillarioid]] [[lycopsid]]s, and [[Aneurophyton|aneurophyte]] and [[Archaeopteris|archaeopterid]] [[progymnosperm]]s.<ref name="Algeo1998" /> Fish were also undergoing a huge radiation, and [[tetrapodomorphs]], such as the Frasnian-age ''[[Tiktaalik]]'', were beginning to evolve leg-like structures.<ref>{{cite journal | url = http://www.nature.com/news/2006/060403/full/060403-7.html | title = The fish that crawled out of the water | year = 2006 | journal = Nature | doi = 10.1038/news060403-7 | access-date = 2006-04-06 | archive-url = https://web.archive.org/web/20060411162634/http://www.nature.com/news/2006/060403/full/060403-7.html | archive-date = 2006-04-11 | url-status = live | last1 = Dalton | first1 = Rex | pages = news060403–7 | s2cid = 129031187 | url-access = subscription }}</ref><ref>{{cite journal | journal = [[Nature (journal)|Nature]] | volume = 440 | pages = 764–771 | date = 6 April 2006 | doi = 10.1038/nature04637 | title = The pectoral fin of ''Tiktaalik roseae'' and the origin of the tetrapod limb | author = Neil H. Shubin, Edward B. Daeschler and Farish A. Jenkins Jr | pmid = 16598250 | issue = 7085| bibcode = 2006Natur.440..764S | s2cid = 4412895 }}</ref>

==Extinction patterns==
The Kellwasser event and most other Later Devonian pulses primarily affected the marine community, and had a greater effect on shallow warm-water organisms than on cool-water organisms. The Kellwasser event's effects were also stronger at low latitudes than high ones.<ref>{{cite journal |last1=Ma |first1=Kunyuan |last2=Hinnov |first2=Linda |last3=Zhang |first3=Xinsong |last4=Gong |first4=Yiming |date=August 2022 |title=Astronomical climate changes trigger Late Devonian bio- and environmental events in South China |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818122001412 |journal=[[Global and Planetary Change]] |volume=215 |article-number=103874 |doi=10.1016/j.gloplacha.2022.103874 |bibcode=2022GPC...21503874M |access-date=22 November 2022|url-access=subscription }}</ref> Large differences are observed between the biotas before and after the Frasnian-Famennian boundary, demonstrating the extinction event's magnitude.<ref>{{Cite journal |last1=Gutak |first1=Jaroslav M. |last2=Ruban |first2=Dmitry A. |last3=Ermolaev |first3=Vladimir A. |date=1 February 2023 |title=Devonian geoheritage of Siberia: A case of the northwestern Kemerovo region of Russia |journal=[[Heliyon]] |volume=9 |issue=2 |article-number=e13288 |doi=10.1016/j.heliyon.2023.e13288 |pmid=36816259 |pmc=9936521 |issn=2405-8440 |doi-access=free |bibcode=2023Heliy...913288G }}</ref>

=== Reef destruction ===
[[File:StromatoporoidSideDevColumbus.jpg|thumb|220px|Side view of a [[stromatoporoid]] showing laminae and pillars; Columbus Limestone (Devonian) of Ohio|left]]
The most hard-hit biological category affected by the Kellwasser event were the calcite-based reef-builders of the great Devonian reef-systems, including the [[stromatoporoid]] sponges and the [[rugosa|rugose]] and [[tabulate]] [[coral]]s.<ref name=Algeo1998/><ref>{{cite journal |last1=Zapalski |first1=Mikołaj K. |last2=Berkowski |first2=Błażej |last3=Wrzołek |first3=Tomasz |date=23 March 2016 |title=Tabulate Corals after the Frasnian/Famennian Crisis: A Unique Fauna from the Holy Cross Mountains, Poland |journal=[[PLOS ONE]] |volume=11 |issue=3 |article-number=e0149767 |doi=10.1371/journal.pone.0149767 |pmid=27007689 |pmc=4807921 |bibcode=2016PLoSO..1149767Z |doi-access=free }}</ref><ref>{{Cite journal |last=House |first=Michael R |date=20 June 2002 |title=Strength, timing, setting and cause of mid-Palaeozoic extinctions |url=https://www.sciencedirect.com/science/article/pii/S0031018201004710 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=181 |issue=1 |pages=5–25 |doi=10.1016/S0031-0182(01)00471-0 |bibcode=2002PPP...181....5H |issn=0031-0182 |access-date=11 November 2023|url-access=subscription }}</ref> It left communities of [[Beloceratidae|beloceratids]] and [[manticoceratids]] devastated.<ref>{{Cite web |title=Kellwasser Event {{!}} paleontology {{!}} Britannica |url=https://www.britannica.com/topic/Kellwasser-Event |access-date=2023-01-31 |website=www.britannica.com |language=en}}</ref> Following the Kellwasser event, reefs of the Famennian were primarily dominated by siliceous sponges and calcifying bacteria, producing structures such as [[oncolite]]s and [[stromatolites]],<ref>{{Cite journal |last=Copper |first=Paul |date=2002-06-20 |title=Reef development at the Frasnian/Famennian mass extinction boundary |url=https://www.sciencedirect.com/science/article/pii/S0031018201004722 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=181 |issue=1 |pages=27–65 |doi=10.1016/S0031-0182(01)00472-2 |bibcode=2002PPP...181...27C |issn=0031-0182|url-access=subscription }}</ref> although there is evidence this shift in reef composition began prior to the Frasnian-Famennian boundary.<ref>{{cite journal |last1=Shen |first1=Jianwei |last2=Webb |first2=Gregory E. |last3=Qing |first3=Hairuo |date=16 November 2010 |title=Microbial mounds prior to the Frasnian-Famennian mass extinctions, Hantang, Guilin, South China |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-3091.2010.01158.x |journal=Sedimentology |volume=57 |issue=7 |pages=1615–1639 |doi=10.1111/j.1365-3091.2010.01158.x |bibcode=2010Sedim..57.1615S |s2cid=140165154 |access-date=26 January 2023|url-access=subscription }}</ref> The collapse of the reef system was so stark that it would take until the Mesozoic for reefs to recover their Middle Devonian extent. Mesozoic and modern reefs are based on [[Scleractinia|scleractinian]] ("stony") corals, which would not evolve until the Triassic period. Devonian reef-builders are entirely extinct in the modern day: Stromatoporoids died out in the end-Devonian Hangenberg event, while rugose and tabulate corals went extinct at the [[Permian–Triassic extinction event|Permian-Triassic extinction]].

=== Marine arthropods ===
[[Trilobite|Trilobites]] were profoundly affected by the extinction event. Three [[trilobite]] orders went extinct: [[Corynexochida]], [[Harpetida]], and [[Odontopleurida]]. All three had been declining since the [[Taghanic event]] at the end of the Givetian, which also killed off the order [[Lichida]]. This left only two trilobites orders in the Famennian: [[Phacopida]] and [[Proetida]]. Trilobites which survived the Kellwasser event tended to prefer deep environments and tropical latitudes. A few small groups managed to thrive in the aftermath, namely [[Phacopidae|phacopids]] and cyrtosymboline [[Phillipsiidae|phillipsiids]]. These warm-water specialists would suffer during the cold snap of the Hangenberg event, cutting the post-Kellwasser recovery short.<ref>{{Cite journal |last1=Bault |first1=Valentin |last2=Balseiro |first2=Diego |last3=Monnet |first3=Claude |last4=Crônier |first4=Catherine |date=2022-07-01 |title=Post-Ordovician trilobite diversity and evolutionary faunas |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825222001192 |journal=Earth-Science Reviews |volume=230 |article-number=104035 |doi=10.1016/j.earscirev.2022.104035 |bibcode=2022ESRv..23004035B |issn=0012-8252|url-access=subscription }}</ref>

[[Trilobite]]s evolved smaller eyes in the run-up to the Kellwasser event, with eye size increasing again afterwards. This suggests vision was less important around the event, perhaps due to increasing water depth or turbidity. The brims of trilobites (i.e. the rims of their heads) also expanded across this period. The brims are thought to have served a respiratory purpose, and the increasing anoxia of waters led to an increase in their brim area in response.

Among [[Ostracod|ostracods]], no families went extinct, but small-scale taxonomic units were severely impacted. Around 80% of ostracod species died out worldwide, though the extinction rate reached 91% in Eastern Europe. Both shallow and deep marine ("Thuringian") ostracods were impacted. Ostracods which could tolerate oxygen stress survived the extinction more easily, and [[Endemism|endemic]] deep marine species diversified quickly in the aftermath.<ref>{{Cite journal |last1=Guillam |first1=Elvis |last2=Forel |first2=Marie-Béatrice |last3=Crasquin |first3=Sylvie |date=2024-09-01 |title=Marine ostracod faunas through the Late Devonian extinction events. Part I: The Kellwasser event |journal=Earth-Science Reviews |volume=256 |article-number=104866 |doi=10.1016/j.earscirev.2024.104866 |bibcode=2024ESRv..25604866G |issn=0012-8252|doi-access=free }}</ref>

=== Other marine invertebrates ===
Further taxa to be starkly affected include the [[brachiopod]]s, [[ammonite]]s, [[conodont]]s, [[acritarch]] and [[graptolites]]. [[Cystoids]] disappeared during this event. The surviving taxa show morphological trends through the event. Atrypid and [[Strophomenida|strophomenid]] brachiopods became rarer, replaced in many niches by [[Productida|productids]], whose spiny shells made them more resistant to predation and environmental disturbances.<ref>{{cite journal |last1=Brisson |first1=Sarah K. |last2=Pier |first2=Jaleigh Q. |last3=Beard |first3=J. Andrew |last4=Fernandes |first4=Anjali M. |last5=Bush |first5=Andrew M. |date=5 April 2023 |title=Niche conservatism and ecological change during the Late Devonian mass extinction |journal=[[Proceedings of the Royal Society B: Biological Sciences]] |volume=290 |issue=1996 |article-number=20222524 |doi=10.1098/rspb.2022.2524 |pmid=37015271 |pmc=10072939 }}</ref>

As with most extinction events, specialist taxa occupying small niches were harder hit than generalists.<ref name="McGhee" /> Marine invertebrates that lived in warmer ecoregions were devastated more compared to those living in colder biomes.<ref>{{Cite journal |last=Copper |first=Paul |date=1 April 1977 |title=Paleolatitudes in the Devonian of Brazil and the Frasnian-Famennian mass extinction |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=21 |issue=3 |pages=165–207 |doi=10.1016/0031-0182(77)90020-7 |bibcode=1977PPP....21..165C |issn=0031-0182 }}</ref> 

=== Vertebrates ===
[[File:Tiktaalik restoration by ObsidianSoul 01.png|thumb|190px|''[[Tiktaalik]]'', an early air-breathing [[Elpistostegalia|elpistostegalian]]. They were among the vertebrates which died out due to the Kellwasser event]]Vertebrates were not strongly affected by the Kellwasser event, but still experienced some diversity loss. Around half of placoderm families died out, primarily species-poor bottom-feeding groups. More diverse placoderm families survived the event only to succumb in the Hangenberg event at the end of the Devonian. Most lingering agnathan (jawless fish) groups, such as [[Osteostraci|osteostracans]], [[Galeaspida|galeaspids]], and [[Heterostraci|heterostracans]], also went extinct by the end of the Frasnian. The jawless [[Thelodonti|thelodonts]] only barely survived, succumbing early in the Famennian.<ref name="Friedman-2012">{{Cite journal |last1=Friedman |first1=Matt |last2=Sallan |first2=Lauren Cole |date=2012 |title=Five hundred million years of extinction and recovery: a phanerozoic survey of large-scale diversity patterns in fishes: EXTINCTION AND RECOVERY IN FISHES |journal=[[Palaeontology (journal)|Palaeontology]] |language=en |volume=55 |issue=4 |pages=707–742 |doi=10.1111/j.1475-4983.2012.01165.x|s2cid=59423401 |doi-access=free |bibcode=2012Palgy..55..707F }}</ref> The shape of conodonts' feeding apparatus varied with [[Δ18O|the oxygen isotope ratio]], and thus with the sea water temperature; this may relate to their occupying different [[trophic level]]s as nutrient input changed.<ref name="Balter">{{cite journal|last1=Balter|first1=Vincent|last2=Renaud|first2=Sabrina|last3=Girard|first3=Catherine|last4=Joachimski|first4=Michael M.|date=November 2008|title=Record of climate-driven morphological changes in 376&nbsp;Ma Devonian fossils|journal=[[Geology (journal)|Geology]]|volume=36|issue=11|page=907|bibcode=2008Geo....36..907B|doi=10.1130/G24989A.1}}</ref> Among freshwater and shallow marine [[Tetrapodomorpha|tetrapodomorph]] fish, the tetrapod-like [[Elpistostegalia|elpistostegalians]] (such as ''[[Tiktaalik]]'') disappeared at the Frasnian-Famennian boundary. True [[Tetrapod|tetrapods]] (defined as four-limbed vertebrates with digits) survived and experienced an evolutionary radiation following the Kellwasser extinction,<ref name="JenniferClack2007">{{cite journal |last1=Clack |first1=Jennifer A. |date=13 August 2007 |title=Devonian climate change, breathing, and the origin of the tetrapod stem group |url=https://academic.oup.com/icb/article/47/4/510/632798 |journal=[[Integrative and Comparative Biology]] |volume=47 |issue=4 |pages=510–523 |doi=10.1093/icb/icm055 |pmid=21672860 |access-date=15 January 2023|url-access=subscription }}</ref> though their [[fossils]] are rare until the mid-to-late Famennian.

===Magnitude of diversity loss===
The late Devonian crash in [[biodiversity]] was more drastic than the familiar [[Cretaceous–Paleogene extinction event|extinction event]] that closed the [[Cretaceous]]. A recent survey (McGhee 1996) estimates that 22% of all the '[[family (biology)|families]]' of marine animals (largely [[invertebrate]]s) were eliminated. The family is a great unit, and to lose so many signifies a deep loss of ecosystem diversity. On a smaller scale, 57% of genera and at least 75% of species did not survive into the Carboniferous. These latter estimates<ref group="lower-alpha">The species estimate is the toughest to assess and most likely to be adjusted.</ref> need to be treated with a degree of caution, as the estimates of species loss depend on surveys of Devonian marine taxa that are perhaps not well enough known to assess their true rate of losses, so it is difficult to estimate the effects of differential preservation and [[sampling bias]]es during the Devonian.

==Duration and timing==
Extinction rates appear to have been higher than the background rate for an extended interval covering the last 20–25 million years of the Devonian. During this time, about eight to ten distinct events can be seen, of which two, the Kellwasser and the Hangenberg events, stand out as particularly severe.<ref name=Algeo2001>{{cite book|author=Algeo, T.J., S.E. Scheckler and J. B. Maynard|chapter=Effects of the Middle to Late Devonian spread of vascular land plants on weathering regimes, marine biota, and global climate|pages=13–236|editor1=P.G. Gensel |editor2=D. Edwards |year= 2001|title=Plants Invade the Land: Evolutionary and Environmental Approaches|publisher=Columbia Univ. Press: New York.}}</ref> The Kellwasser event was preceded by a longer period of prolonged [[biodiversity loss]].<ref name=Streel2000>{{cite journal|author=Streel, M.|author2=Caputo, M.V. |author3=Loboziak, S. |author4= Melo, J.H.G. |year=2000|title=Late Frasnian--Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations|journal=[[Earth-Science Reviews]]|volume=52|issue=1–3|doi=10.1016/S0012-8252(00)00026-X|pages=121–173|bibcode=2000ESRv...52..121S|hdl=2268/156563 |url=http://orbi.ulg.ac.be/handle/2268/156563 |hdl-access=free}}</ref> 

The Kellwasser event, named for its [[Type locality (geology)|type locality]], the Kellwassertal in [[Lower Saxony]], [[Germany]], is the term given to the extinction pulse that occurred near the Frasnian–Famennian boundary (372.2 ± 1.6 Ma). Most references to the "Late Devonian extinction" are in fact referring to the Kellwasser, which was the first event to be detected based on marine invertebrate record and was the most severe of the extinction crises of the Late Devonian.<ref>{{cite journal |last1=Percival |first1=L. M. E. |last2=Davies |first2=J. H. F. L. |last3=Schaltegger |first3=Urs |last4=De Vleeschouwer |first4=D. |last5=Da Silva |first5=A.-C. |last6=Föllmi |first6=K. B. |date=22 June 2018 |title=Precisely dating the Frasnian–Famennian boundary: implications for the cause of the Late Devonian mass extinction |journal=[[Scientific Reports]] |volume=8 |issue=1 |page=9578 |doi=10.1038/s41598-018-27847-7 |pmid=29934550 |pmc=6014997 |bibcode=2018NatSR...8.9578P }}</ref> There may in fact have been two closely spaced events here, as shown by the presence of two distinct anoxic shale layers.<ref>{{cite journal |last1=Riquier |first1=Laurent |last2=Tribovillard |first2=Nicolas |last3=Averbuch |first3=Olivier |last4=Devleeschuwer |first4=Xavier |last5=Riboulleau |first5=Armelle |date=30 September 2006 |title=The Late Frasnian Kellwasser horizons of the Harz Mountains (Germany): Two oxygen-deficient periods resulting from different mechanisms |url=https://www.sciencedirect.com/science/article/abs/pii/S0009254106001410 |journal=[[Chemical Geology]] |volume=233 |issue=1–2 |pages=137–155 |doi=10.1016/j.chemgeo.2006.02.021 |bibcode=2006ChGeo.233..137R |access-date=15 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Joachimski |first1=Michael M. |last2=Buggisch |first2=Werner |date=1 August 1993 |title=Anoxic events in the late Frasnian—Causes of the Frasnian-Famennian faunal crisis? |url=https://pubs.geoscienceworld.org/gsa/geology/article/21/8/675/205899/Anoxic-events-in-the-late-Frasnian-Causes-of-the |journal=[[Geology (journal)|Geology]] |volume=21 |issue=8 |pages=675–678 |doi=10.1130/0091-7613(1993)021<0675:AEITLF>2.3.CO;2 |bibcode=1993Geo....21..675J |access-date=15 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Renaud |first1=Sabrina |last2=Girard |first2=Catherine |date=15 February 1999 |title=Strategies of survival during extreme environmental perturbations: evolution of conodonts in response to the Kellwasser crisis (Upper Devonian) |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018298001382 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=146 |issue=1–4 |pages=19–32 |doi=10.1016/S0031-0182(98)00138-2 |bibcode=1999PPP...146...19R |access-date=15 January 2023|url-access=subscription }}</ref>

There is evidence that the Kellwasser event was a two-pulsed event, with the two extinction pulses being separated by an interval of approximately 800,000 years. The second pulse was more severe than the first.<ref>{{cite journal |last1=Pier |first1=Jaleigh Q. |last2=Brisson |first2=Sarah K. |last3=Beard |first3=J. Andrew |last4=Hren |first4=Michael T. |last5=Bush |first5=Andrew M. |date=21 December 2021 |title=Accelerated mass extinction in an isolated biota during Late Devonian climate changes |journal=[[Scientific Reports]] |volume=11 |issue=1 |page=24366 |doi=10.1038/s41598-021-03510-6 |pmid=34934059 |pmc=8692332 |bibcode=2021NatSR..1124366P }}</ref>

==Potential causes==
Since the Kellwasser-related extinctions occurred over such a long time, it is difficult to assign a single cause, and indeed to separate cause from effect. From the end of the Middle Devonian ({{val|382.7|1.6|u=Ma}}), into the Late Devonian ({{val|382.7|1.6|u=Ma}} to {{val|358.9|0.4|u=Ma}}), several environmental changes can be detected from the sedimentary record,<!--this needs to be more specific to transmit information--> which directly affected organisms and caused extinction. What caused these changes is somewhat more open to debate. Possible triggers for the Kellwasser event are as follows:

===Weathering and anoxia===
During the [[Late Silurian]] and Devonian, land plants, assisted by fungi,<ref name="LutzoniEtAl2018">{{cite journal |last1=Lutzoni |first1=François |last2=Nowak |first2=Michael D. |last3=Alfaro |first3=Michael E. |last4=Reeb |first4=Valérie |last5=Miadlikowska |first5=Jolanta |last6=Krug |first6=Michael |last7=Arnold |first7=A. Elizabeth |last8=Lewis |first8=Louise A. |last9=Swofford |first9=David L. |last10=Hibbett |first10=David |last11=Hilu |first11=Khidir |last12=James |first12=Timothy Y. |last13=Quandt |first13=Dietmar |last14=Magallón |first14=Susana |date=21 December 2018 |title=Contemporaneous radiations of fungi and plants linked to symbiosis |journal=[[Nature Communications]] |volume=9 |issue=1 |page=5451 |doi=10.1038/s41467-018-07849-9 |pmid=30575731 |pmc=6303338 |bibcode=2018NatCo...9.5451L }}</ref><ref name="Retallack2022GondwanaResearch">{{cite journal |last1=Retallack |first1=Gregory J. |date=June 2022 |title=Ordovician-Devonian lichen canopies before evolution of woody trees |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X22000247 |journal=[[Gondwana Research]] |volume=106 |pages=211–223 |doi=10.1016/j.gr.2022.01.010 |bibcode=2022GondR.106..211R |s2cid=246320087 |access-date=22 November 2022|url-access=subscription }}</ref> underwent a hugely significant phase of evolution known as the [[Silurian-Devonian Terrestrial Revolution]].<ref name="SilurianDevonianTerrestrialRevolution">{{cite journal |last1=Capel |first1=Elliot |last2=Cleal |first2=Christopher J. |last3=Xue |first3=Jinzhuang |last4=Monnet |first4=Claude |last5=Servais |first5=Thomas |last6=Cascales-Miñana |first6=Borja |date=August 2022 |title=The Silurian–Devonian terrestrial revolution: Diversity patterns and sampling bias of the vascular plant macrofossil record |journal=[[Earth-Science Reviews]] |volume=231 |article-number=104085 |doi=10.1016/j.earscirev.2022.104085 |bibcode=2022ESRv..23104085C |s2cid=249616013 |doi-access=free |hdl=20.500.12210/76731 |hdl-access=free }}</ref><ref name="SilurianDevonianTerrestrialRevolutionChina">{{cite journal |last1=Xue |first1=Jinzhuang |last2=Huang |first2=Pu |last3=Wang |first3=Deming |last4=Xiong |first4=Conghui |last5=Liu |first5=Le |last6=Basinger |first6=James F. |date=May 2018 |title=Silurian-Devonian terrestrial revolution in South China: Taxonomy, diversity, and character evolution of vascular plants in a paleogeographically isolated, low-latitude region |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825217306591 |journal=[[Earth-Science Reviews]] |volume=180 |pages=92–125 |doi=10.1016/j.earscirev.2018.03.004 |bibcode=2018ESRv..180...92X |access-date=15 January 2023|url-access=subscription }}</ref> Their maximum height went from 30 cm at the start of the Devonian, to {{nowrap|30 m}} archaeopterids,<ref name=Beck>{{cite journal|first=C.B. |last=Beck|url=https://deepblue.lib.umich.edu/bitstream/handle/2027.42/141981/ajb214953.pdf;jsessionid=0F631BFED2336656C5828043FE60D867?sequence=1|date=April 1962 |title=Reconstructions of ''Archaeopteris'', and further consideration of its phylogenetic position |journal=American Journal of Botany |volume=49 |issue=4|pages=373–382|doi=10.1002/j.1537-2197.1962.tb14953.x|bibcode=1962AmJB...49..373B |hdl=2027.42/141981|hdl-access=free}}</ref> at the end of the period. This increase in height was made possible by the evolution of advanced vascular systems, which permitted the growth of complex branching and rooting systems,<ref name="Algeo1998">{{cite journal |author=Algeo, T.J. |last2=Scheckler |first2=S. E. |year=1998 |title=Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events |journal=[[Philosophical Transactions of the Royal Society B: Biological Sciences]] |volume=353 |issue=1365 |pages=113–130 |doi=10.1098/rstb.1998.0195 |pmc=1692181}}</ref> facilitating their ability to colonise drier areas previously off limits to them.<ref>{{cite journal |last1=Gurung |first1=Khushboo |last2=Field |first2=Katie J. |last3=Batterman |first3=Sarah J. |last4=Goddéris |first4=Yves |last5=Donnadieu |first5=Yannick |last6=Porada |first6=Philipp |last7=Taylor |first7=Lyla L. |last8=Mills |first8=Benjamin J. W. |date=4 August 2022 |title=Climate windows of opportunity for plant expansion during the Phanerozoic |journal=[[Nature Communications]] |volume=13 |issue=1 |page=4530 |doi=10.1038/s41467-022-32077-7 |pmid=35927259 |pmc=9352767 |bibcode=2022NatCo..13.4530G |s2cid=245030483 }}</ref> In conjunction with this, the evolution of seeds permitted reproduction and dispersal in areas which were not waterlogged, allowing plants to colonise previously inhospitable inland and upland areas.<ref name=Algeo1998/> The two factors combined to greatly magnify the role of plants on the global scale. In particular, ''[[Archaeopteris]]'' forests expanded rapidly during the closing ages of the Devonian.<ref>{{cite journal |last1=Stein |first1=William E. |last2=Berry |first2=Christopher M. |last3=Morris |first3=Jennifer L. |last4=Hernick |first4=Linda VanAller |last5=Mannolini |first5=Frank |last6=Ver Straeten |first6=Charles |last7=Landing |first7=Ed |last8=Marshall |first8=John E. A. |last9=Wellman |first9=Charles H. |last10=Beerling |first10=David J. |last11=Leake |first11=Jonathan R. |date=3 February 2020 |title=Mid-Devonian Archaeopteris Roots Signal Revolutionary Change in Earliest Fossil Forests |journal=[[Current Biology]] |volume=30 |issue=3 |pages=321–331 |doi=10.1016/j.cub.2019.11.067 |pmid=31866369 |s2cid=209422168 |doi-access=free |bibcode=2020CBio...30E.421S }}</ref> These tall trees required deep rooting systems to acquire water and nutrients, and provide anchorage. These systems broke up the upper layers of bedrock and stabilized a deep layer of soil, which would have been of the order of metres thick. In contrast, early Devonian plants bore only rhizoids and rhizomes that could penetrate no more than a few centimeters. The mobilization of a large portion of soil had a huge effect: soil promotes [[weathering]], the chemical breakdown of rocks, releasing ions which are nutrients for plants and algae.<ref name="Algeo1998" />

The relatively sudden input of nutrients into river water as rooted plants expanded into upland regions may have caused [[eutrophication]], [[harmful algal bloom]] and subsequent [[anoxic water|anoxia]].<ref>{{Cite journal |last1=Gong |first1=Yiming |last2=Xu |first2=Ran |last3=Tang |first3=Zhongdao |last4=Si |first4=Yuanlan |last5=Li |first5=Baohua |date=1 October 2005 |title=Relationships between bacterial-algal proliferating and mass extinction in the Late Devonian Frasnian-Famennian transition: Enlightening from carbon isotopes and molecular fossils |url=http://link.springer.com/10.1360/02yd0346 |journal=Science in China Series D: Earth Sciences |language=en |volume=48 |issue=10 |pages=1656–1665 |doi=10.1360/02yd0346 |bibcode=2005ScChD..48.1656G |s2cid=130283448 |issn=1006-9313 |access-date=11 November 2023|url-access=subscription }}</ref><ref name="Balter" /> For example, during an algal bloom, organic material formed at the surface can sink at such a rate that decomposition of dead organisms uses up all available oxygen, creating anoxic conditions and suffocating bottom-dwelling fish. The fossil reefs of the Frasnian were dominated by [[Stromatoporoidea|stromatoporoids]] and (to a lesser degree) corals—organisms which only thrive in low-nutrient conditions. Therefore, the postulated influx of high levels of nutrients may have caused an extinction.<ref name=Algeo1998/><ref>{{cite journal |last1=Smart |first1=Matthew S. |last2=Filippelli |first2=Gabriel |last3=Gilhooly III |first3=William P. |last4=Marshall |first4=John E.A. |last5=Whiteside |first5=Jessica H. |title=Enhanced terrestrial nutrient release during the Devonian emergence and expansion of forests: Evidence from lacustrine phosphorus and geochemical records |journal=GSA Bulletin |date=9 November 2022 |doi=10.1130/B36384.1|doi-access=free |hdl=1805/36402 |hdl-access=free }}</ref> Anoxic conditions correlate better with biotic crises than phases of cooling, suggesting anoxia may have played the dominant role in extinction.<ref name=Algeo1995>{{cite journal|author=Algeo, T.J.|author2=Berner, R.A.|author3=Maynard, J.B.|author4=Scheckler, S.E.|author5=Archives, G.S.A.T.|year=1995|title=Late Devonian Oceanic Anoxic Events and Biotic Crises: "Rooted" in the Evolution of Vascular Land Plants?|journal=GSA Today|volume=5|issue=3|url=https://homepages.uc.edu/~algeot/Algeo-Dev95.pdf}}</ref> Evidence exists of a rapid increase in the rate of organic carbon burial and for widespread anoxia in oceanic bottom waters.<ref>{{cite journal |last1=Joachimski |first1=Michael M. |last2=Ostertag-Henning |first2=Christian |last3=Pancost |first3=Richard D. |last4=Strauss |first4=Harald |last5=Freeman |first5=Katherine H. |last6=Littke |first6=Ralf |last7=Sinninghe Damsté |first7=Jaap S. |last8=Racki |first8=Grzegorz |date=1 May 2001 |title=Water column anoxia, enhanced productivity and concomitant changes in δ13C and δ34S across the Frasnian–Famennian boundary (Kowala — Holy Cross Mountains/Poland) |url=https://www.sciencedirect.com/science/article/abs/pii/S000925410000365X |journal=[[Chemical Geology]] |volume=175 |issue=1–2 |pages=109–131 |doi=10.1016/S0009-2541(00)00365-X |bibcode=2001ChGeo.175..109J |access-date=26 January 2023|url-access=subscription }}</ref><ref name="Algeo1998" /> Signs of anoxia in shallow waters have also been described from a variety of localities.<ref>{{cite journal |last1=Bond |first1=David P. G. |last2=Zatoń |first2=Michał |last3=Wignall |first3=Paul B. |last4=Marynowski |first4=Leszek |date=11 March 2013 |title=Evidence for shallow-water 'Upper Kellwasser' anoxia in the Frasnian–Famennian reefs of Alberta, Canada |url=https://onlinelibrary.wiley.com/doi/full/10.1111/let.12014 |journal=[[Lethaia]] |volume=46 |issue=3 |pages=355–368 |doi=10.1111/let.12014 |bibcode=2013Letha..46..355B |access-date=12 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Carmichael |first1=Sarah K. |last2=Waters |first2=Johnny A. |last3=Suttner |first3=Thomas J. |last4=Kido |first4=Erika |last5=DeReuil |first5=Aubry A. |date=1 April 2014 |title=A new model for the Kellwasser Anoxia Events (Late Devonian): Shallow water anoxia in an open oceanic setting in the Central Asian Orogenic Belt |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018214000790 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=399 |pages=394–403 |doi=10.1016/j.palaeo.2014.02.016 |bibcode=2014PPP...399..394C |access-date=12 January 2023|url-access=subscription }}</ref><ref>{{cite book |last1=Bond |first1=David P. G. |url=https://www.sciencedirect.com/bookseries/developments-in-palaeontology-and-stratigraphy/vol/20/suppl/C |title=Understanding Late Devonian And Permian-Triassic Biotic and Climatic Events: Towards an Integrated Approach |last2=Wignall |first2=Paul B. |publisher=Elsevier |year=2005 |isbn=978-0-444-52127-9 |editor-last1=Over |editor-first1=D. J. |series=Developments in Palaeontology and Stratigraphy |volume=20 |pages=225–262 |chapter=Evidence for Late Devonian (Kellwasser) anoxic events in the Great Basin, Western United States |doi=10.1016/S0920-5446(05)80009-3 |editor-last2=Morrow |editor-first2=J. R. |editor-last3=Wignall |editor-first3=Paul B. |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/S0920544605800093}}</ref> Good evidence has been found for high-frequency sea-level changes around the Frasnian–Famennian Kellwasser event, with one [[Marine transgression|sea-level rise]] associated with the onset of anoxic deposits;<ref name="Bond2008">{{cite journal |author1=David P. G. Bond |author2=Paul B. Wignalla |year=2008 |title=The role of sea-level change and marine anoxia in the Frasnian-Famennian (Late Devonian) mass extinction |url=http://eprints.whiterose.ac.uk/3460/1/bondb2.pdf |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=263 |issue=3–4 |pages=107–118 |bibcode=2008PPP...263..107B |doi=10.1016/j.palaeo.2008.02.015}}</ref> marine transgressions likely helped spread deoxygenated waters.<ref name=":0" /> Evidence exists for the modulation of the intensity of anoxia by [[Milankovitch cycles]] as well.<ref>{{cite journal |last1=Da Silva |first1=Anne-Christine |last2=Sinesael |first2=Matthias |last3=Claeys |first3=Philippe |last4=Davies |first4=Joshua H. M. L. |last5=De Winter |first5=Niels J. |last6=Percival |first6=L. M. E. |last7=Schaltegger |first7=Urs |last8=De Vleeschouwer |first8=David |date=31 July 2020 |title=Anchoring the Late Devonian mass extinction in absolute time by integrating climatic controls and radio-isotopic dating |journal=[[Scientific Reports]] |volume=10 |issue=1 |page=12940 |bibcode=2020NatSR..1012940D |doi=10.1038/s41598-020-69097-6 |pmc=7395115 |pmid=32737336 |s2cid=220881345}}</ref><ref>{{Cite journal |last1=De Vleeschouwer |first1=David |last2=Rakociński |first2=Michał |last3=Racki |first3=Grzegorz |last4=Bond |first4=David P. G. |last5=Sobień |first5=Katarzyna |last6=Claeys |first6=Philippe |date=1 March 2013 |title=The astronomical rhythm of Late-Devonian climate change (Kowala section, Holy Cross Mountains, Poland) |url=https://www.sciencedirect.com/science/article/pii/S0012821X13000241 |journal=[[Earth and Planetary Science Letters]] |volume=365 |pages=25–37 |doi=10.1016/j.epsl.2013.01.016 |bibcode=2013E&PSL.365...25D |issn=0012-821X |access-date=11 November 2023|url-access=subscription }}</ref> Negative δ<sup>238</sup>U excursions concomitant with both the Lower and Upper Kellwasser events provide direct evidence for an increase in anoxia.<ref>{{Cite journal |last1=White |first1=David A. |last2=Elrick |first2=Maya |last3=Romaniello |first3=Stephen |last4=Zhang |first4=Feifei |date=1 December 2018 |title=Global seawater redox trends during the Late Devonian mass extinction detected using U isotopes of marine limestones |journal=[[Earth and Planetary Science Letters]] |volume=503 |pages=68–77 |doi=10.1016/j.epsl.2018.09.020 |s2cid=134806864 |issn=0012-821X |doi-access=free |bibcode=2018E&PSL.503...68W }}</ref> Photic zone [[euxinia]], documented by concurrent negative ∆<sup>199</sup>Hg and positive δ<sup>202</sup>Hg excursions, occurred in the North American Devonian Seaway.<ref name=":1">{{Cite journal |last1=Zheng |first1=Wang |last2=Gilleaudeau |first2=Geoffrey J. |last3=Algeo |first3=Thomas J. |last4=Zhao |first4=Yaqiu |last5=Song |first5=Yi |last6=Zhang |first6=Yuanming |last7=Sahoo |first7=Swapan K. |last8=Anbar |first8=Ariel D. |last9=Carmichael |first9=Sarah K. |last10=Xie |first10=Shucheng |last11=Liu |first11=Cong-Qiang |last12=Chen |first12=Jiubin |date=1 July 2023 |title=Mercury isotope evidence for recurrent photic-zone euxinia triggered by enhanced terrestrial nutrient inputs during the Late Devonian mass extinction |journal=[[Earth and Planetary Science Letters]] |volume=613 |article-number=118175 |doi=10.1016/j.epsl.2023.118175 |bibcode=2023E&PSL.61318175Z |s2cid=258636301 |issn=0012-821X |doi-access=free }}</ref> Elevated [[molybdenum]] concentrations further support widespread euxinic waters.<ref>{{Cite journal |last=Lash |first=Gary G. |date=1 May 2015 |title=A multiproxy analysis of the Frasnian-Famennian transition in western New York State, U.S.A |url=https://www.sciencedirect.com/science/article/pii/S0031018216307362 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=473 |pages=108–122 |doi=10.1016/j.palaeo.2017.02.032 |issn=0031-0182 |access-date=11 November 2023|url-access=subscription }}</ref>

The timing, magnitude, and causes of Kellwasser anoxia remain poorly understood.<ref name="CarmichaelEtAl2019" /> Anoxia was not omnipresent across the globe; in some regions, such as [[South China]], the Frasnian-Famennian boundary instead shows evidence of increased oxygenation of the seafloor.<ref>{{cite journal |last1=Cui |first1=Yixin |last2=Shen |first2=Bing |last3=Sun |first3=Yuanlin |last4=Ma |first4=Haoran |last5=Chang |first5=Jieqiong |last6=Li |first6=Fangbing |last7=Lang |first7=Xianguo |last8=Peng |first8=Yongbo |date=July 2021 |title=A pulse of seafloor oxygenation at the Late Devonian Frasnian-Famennian boundary in South China |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825221001525 |journal=[[Earth-Science Reviews]] |volume=218 |article-number=103651 |doi=10.1016/j.earscirev.2021.103651 |bibcode=2021ESRv..21803651C |s2cid=235519724 |access-date=15 January 2023|url-access=subscription }}</ref> Trace metal proxies in black shales from New York state point to anoxic conditions only occurring intermittently, being interrupted by oxic intervals, further indicating that anoxia was not globally synchronous,<ref>{{cite journal |last1=Haddad |first1=Emily E. |last2=Boyer |first2=Diana L. |last3=Droser |first3=Mary L. |last4=Lee |first4=Bridget K. |last5=Lyons |first5=Timothy W. |last6=Love |first6=Gordon D. |date=15 January 2018 |title=Ichnofabrics and chemostratigraphy argue against persistent anoxia during the Upper Kellwasser Event in New York State |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=490 |pages=178–190 |doi=10.1016/j.palaeo.2017.10.025 |bibcode=2018PPP...490..178H |doi-access=free }}</ref> a finding also supported by the prevalence of cyanobacterial mats in the [[Holy Cross Mountains]] in the time period around the Kellwasser event.<ref>{{cite journal |last1=Kazmierczak |first1=J. |last2=Kremer |first2=B. |last3=Racki |first3=Grzegorz |date=7 August 2012 |title=Late Devonian marine anoxia challenged by benthic cyanobacterial mats |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1472-4669.2012.00339.x |journal=Geobiology |volume=10 |issue=5 |pages=371–383 |doi=10.1111/j.1472-4669.2012.00339.x |pmid=22882315 |bibcode=2012Gbio...10..371K |s2cid=42682449 |access-date=26 January 2023|url-access=subscription }}</ref> Evidence from various European sections reveals that Kellwasser anoxia was relegated to epicontinental seas and developed as a result of upwelling of poorly oxygenated waters within ocean basins into shallow waters rather than a global oceanic anoxic event that intruded into epicontinental seas.<ref>{{cite journal |last1=Bond |first1=David P. G. |last2=Wignall |first2=Paul B. |last3=Racki |first3=Grzegorz |date=1 March 2004 |title=Extent and duration of marine anoxia during the Frasnian–Famennian (Late Devonian) mass extinction in Poland, Germany, Austria and France |url=https://pubs.geoscienceworld.org/geolmag/article/141/2/173/65492/Extent-and-duration-of-marine-anoxia-during-the |journal=[[Geological Magazine]] |volume=141 |issue=2 |pages=173–193 |doi=10.1017/S0016756804008866 |bibcode=2004GeoM..141..173B |s2cid=54575059 |access-date=15 January 2023}}</ref>

===Global cooling===
A positive [[Δ18O|δ<sup>18</sup>O]] excursion is observed across the Frasnian-Famennian boundary in brachiopods from [[North America]], Germany, [[Spain]], [[Morocco]], Siberia, and [[China]];<ref>{{Cite journal |last1=van Geldern |first1=R. |last2=Joachimski |first2=M. M. |last3=Day |first3=J. |last4=Jansen |first4=U. |last5=Alvarez |first5=F. |last6=Yolkin |first6=E. A. |last7=Ma |first7=X. -P. |date=6 October 2006 |title=Carbon, oxygen and strontium isotope records of Devonian brachiopod shell calcite |url=https://www.sciencedirect.com/science/article/pii/S0031018206002495 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |series=Evolution of the System Earth in the Late Palaeozoic: Clues from Sedimentary Geochemistry |volume=240 |issue=1 |pages=47–67 |doi=10.1016/j.palaeo.2006.03.045 |bibcode=2006PPP...240...47V |issn=0031-0182 |access-date=11 November 2023|url-access=subscription }}</ref> conodont apatite δ<sup>18</sup>O excursions also occurred at this time.<ref>{{Cite journal |last1=Joachimski |first1=Michael M. |last2=Buggisch |first2=Werner |date=1 August 2002 |title=Conodont apatite δ18O signatures indicate climatic cooling as a trigger of the Late Devonian mass extinction |url=https://pubs.geoscienceworld.org/geology/article/30/8/711-714/192428 |journal=[[Geology (journal)|Geology]] |language=en |volume=30 |issue=8 |page=711 |doi=10.1130/0091-7613(2002)030<0711:CAOSIC>2.0.CO;2 |issn=0091-7613 |access-date=11 November 2023|url-access=subscription }}</ref> A similar positive δ<sup>18</sup>O excursion in phosphates is known from the boundary, corresponding to a removal of atmospheric carbon dioxide and a global cooling event. This oxygen isotope excursion is known from time-equivalent strata in South China and in the western [[Paleo-Tethys Ocean|Palaeotethys]], suggesting it was a globally synchronous climatic change. The concomitance of the drop in global temperatures and the swift decline of metazoan reefs indicates the blameworthiness of global cooling in precipitating the extinction event.<ref>{{cite journal |last1=Huang |first1=Cheng |last2=Joachimski |first2=Michael M. |last3=Gong |first3=Yiming |date=1 August 2018 |title=Did climate changes trigger the Late Devonian Kellwasser Crisis? Evidence from a high-resolution conodont record from South China |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X18302875 |journal=[[Earth and Planetary Science Letters]] |volume=495 |pages=174–184 |doi=10.1016/j.epsl.2018.05.016 |s2cid=133886379 |access-date=15 January 2023|url-access=subscription }}</ref>

The "greening" of the continents during the Silurian-Devonian Terrestrial Revolution that led to them being covered with massive photosynthesizing land plants in the first forests reduced CO<sub>2</sub> levels in the atmosphere.<ref>{{Cite journal|last1=Le Hir|first1=Guillaume|last2=Donnadieu|first2=Yannick|last3=Goddéris|first3=Yves|last4=Meyer-Berthaud|first4=Brigitte|last5=Ramstein|first5=Gilles|last6=Blakey|first6=Ronald C.|date=October 2011|title=The climate change caused by the land plant invasion in the Devonian|url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X11005061|journal=[[Earth and Planetary Science Letters]]|language=en|volume=310|issue=3–4|pages=203–212|doi=10.1016/j.epsl.2011.08.042|bibcode=2011E&PSL.310..203L|access-date=15 January 2023|url-access=subscription}}</ref> Since {{co2}} is a greenhouse gas, reduced levels might have helped produce a chillier climate, in contrast to the warm climate of the Middle Devonian.<ref name=Algeo1998 /> The biological sequestration of carbon dioxide may have ultimately led to the beginning of the [[Late Paleozoic icehouse|Late Palaeozoic Ice Age]] during the Famennian, which has been suggested as a cause of the Hangenberg event.<ref name="Brezinski et al. 2009">{{cite journal |title=Evidence for long-term climate change in Upper Devonian strata of the central Appalachians |doi=10.1016/j.palaeo.2009.10.010 |author1=Brezinski, D.K. |author2=Cecil, C.B. |author3=Skema, V.W. |author4=Kertis, C.A. |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=284 |issue=3–4 |year=2009|pages=315–325 |url=https://www.researchgate.net/publication/223209616|bibcode=2009PPP...284..315B }}</ref>

The weathering of silicate rocks also draws down CO<sub>2</sub> from the atmosphere, and CO<sub>2</sub> sequestration by mountain building has been suggested as a cause of the decline in greenhouse gases during the Frasnian-Famennian transition. This mountain-building may have also enhanced biological sequestration through an increase in nutrient runoff.<ref>{{cite journal |last1=Averbuch |first1=O. |last2=Tribovillard |first2=N. |last3=Devleeschouwer |first3=X. |last4=Riquier |first4=L. |last5=Mistiaen |first5=B. |last6=Van Vliet-Lanoe |first6=B. |date=2 March 2005 |title=Mountain building-enhanced continental weathering and organic carbon burial as major causes for climatic cooling at the Frasnian–Famennian boundary (c. 376 Ma)? |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-3121.2004.00580.x |journal=[[Terra Nova (journal)|Terra Nova]] |volume=17 |issue=1 |pages=25–34 |doi=10.1111/j.1365-3121.2004.00580.x |bibcode=2005TeNov..17...25A |s2cid=140189725 |access-date=23 December 2022|url-access=subscription }}</ref> The combination of silicate weathering and the burial of organic matter to decreased atmospheric CO<sub>2</sub> concentrations from about 15 to three times present levels. Carbon in the form of plant matter would be produced on prodigious scales, and given the right conditions, could be stored and buried, eventually producing vast coal measures (e.g. in China) which locked the carbon out of the atmosphere and into the [[lithosphere]].<ref>Carbon locked in Devonian coal, the earliest of Earth's coal deposits, is currently being returned to the atmosphere.</ref> This reduction in atmospheric {{co2}} would have caused global cooling and resulted in at least one period of late Devonian glaciation (and subsequent sea level fall),<ref name=Algeo1998 /> probably fluctuating in intensity alongside the 40ka [[Milankovic cycle]]. The continued drawdown of organic carbon eventually pulled the Earth out of its [[Greenhouse Earth|greenhouse]] state during the Famennian into the [[Greenhouse Earth|icehouse]] that continued throughout the Carboniferous and Permian.<ref>{{cite book |last1=Rosa |first1=Eduardo L. M. |last2=Isbell |first2=John L. |editor-last1=Alderton |editor-first1=David |editor-last2=Elias |editor-first2=Scott A. |date=2021 |chapter=Late Paleozoic Glaciation |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780081029084000631 |title=Encyclopedia of Geology |edition=2nd |publisher=Academic Press |pages=534–545 |doi=10.1016/B978-0-08-102908-4.00063-1 |isbn=978-0-08-102909-1|s2cid=226643402 }}</ref><ref>{{cite journal |last1=Qie |first1=Wenkun |last2=Algeo |first2=Thomas J. |last3=Luo |first3=Genming |last4=Herrmann |first4=Achim |date=1 October 2019 |title=Global events of the Late Paleozoic (Early Devonian to Middle Permian): A review |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821930625X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=531 |article-number=109259 |doi=10.1016/j.palaeo.2019.109259 |bibcode=2019PPP...53109259Q |s2cid=198423364 |access-date=23 December 2022|url-access=subscription }}</ref>

=== Volcanism ===

[[Magmatism]] was suggested as a cause of the Late Devonian extinction in 2002.<ref name=Krav2002>{{cite journal |author=Kravchinsky, V.A. |author2=K.M. Konstantinov |author3=V. Courtillot |author4=J.-P. Valet |author5=J.I. Savrasov |author6=S.D. Cherniy |author7=S.G. Mishenin |author8=B.S. Parasotka |year=2002 |title=Palaeomagnetism of East Siberian traps and kimberlites: two new poles and palaeogeographic reconstructions at about 360 and 250&nbsp;Ma |journal=Geophysical Journal International |volume=148 |issue=1 |pages=1–33 |doi=10.1046/j.0956-540x.2001.01548.x|bibcode=2002GeoJI.148....1K |doi-access=free }}</ref> The end of the Devonian Period had extremely widespread [[Siberian traps|trap magmatism]] and rifting in the Russian and Siberian platforms, which were situated above the hot mantle plumes and suggested as a cause of the Frasnian / Famennian and end-Devonian extinctions.<ref name=Krav2012>{{cite journal |last=Kravchinsky |first=V. A. |year=2012 |title=Paleozoic large igneous provinces of Northern Eurasia: Correlation with mass extinction events |journal=Global and Planetary Change |volume=86–87 |pages=31–36 |doi=10.1016/j.gloplacha.2012.01.007 |bibcode=2012GPC....86...31K}}</ref> The Viluy Large igneous province, located in the [[Vilyuysk]] region on the [[Siberian Craton]], covers most of the present day north-eastern margin of the Siberian Platform. The triple-junction rift system was formed during the Devonian Period; the Viluy rift is the western remaining branch of the system and two other branches form the modern margin of the Siberian Platform. Volcanic rocks are covered with post Late Devonian–Early Carboniferous sediments.<ref name=Kuz2010>{{cite journal |author=Kuzmin, M.I. |author2=Yarmolyuk, V.V. |author3=Kravchinsky, V.A. |year=2010 |title=Phanerozoic hot spot traces and paleogeographic reconstructions of the Siberian continent based on interaction with the African large low shear velocity province |journal=[[Earth-Science Reviews]] |volume=148 |issue=1–2 |pages=1–33 |doi=10.1016/j.earscirev.2010.06.004 |bibcode=2010ESRv..102...29K}}</ref>
Volcanic rocks, [[Dike (geology)|dyke belts]], and [[Sill (geology)|sills]] that cover more than 320,000&nbsp;km<sup>2</sup>, and a gigantic amount of magmatic material (more than 1&nbsp;million&nbsp;km<sup>3</sup>) formed in the Viluy branch.<ref name=Kuz2010/> The Viluy and [[Dnieper-Donets Rift|Pripyat-Dnieper-Donets]] large igneous provinces were suggested to correlate with the Frasnian / Famennian extinction,<ref name=B2014 /> with the Kola and Timan-Pechora magmatic provinces being suggested to be related to the Hangenberg event at the Devonian-Carboniferous boundary.<ref name=Krav2012/> Viluy magmatism may have injected enough {{CO2|link=yes}} and {{SO2|link=yes}} into the atmosphere to have generated a destabilised [[greenhouse]] and [[ecosystem]], causing rapid global cooling, [[Sea level|sea-level]] falls, and [[Anoxic event|marine anoxia]] to occur during Kellwasser [[Shale|black shale]] deposition.<ref name=B2014>{{cite journal |last1=Bond |first1=D. P. G. |last2=Wignall |first2=P. B. |year=2014 |title=Large igneous provinces and mass extinctions: An update |journal=GSA Special Papers |volume=505 |pages=29–55 |url=http://specialpapers.gsapubs.org/content/505/29.abstract |doi=10.1130/2014.2505(02) |isbn=978-0-8137-2505-5 |access-date=23 December 2022}}</ref><ref>{{cite journal |title=The Late Devonian Frasnian–Famennian event in South China — Patterns and causes of extinctions, sea level changes, and isotope variations |author=Ma, X. P. |display-authors=etal |year=2015 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=448 |pages=224–244 |doi=10.1016/j.palaeo.2015.10.047}}</ref> Viluy Traps activity may have also enabled euxinia by fertilising the oceans with sulphate, increasing rates of microbial sulphate reduction.<ref>{{Cite journal |last1=Sim |first1=Min Sub |last2=Ono |first2=Shuhei |last3=Hurtgen |first3=Matthew T. |date=1 June 2015 |title=Sulfur isotope evidence for low and fluctuating sulfate levels in the Late Devonian ocean and the potential link with the mass extinction event |url=https://www.sciencedirect.com/science/article/pii/S0012821X15001466 |journal=[[Earth and Planetary Science Letters]] |volume=419 |pages=52–62 |doi=10.1016/j.epsl.2015.03.009 |bibcode=2015E&PSL.419...52S |issn=0012-821X |access-date=11 November 2023|hdl=1721.1/109433 |s2cid=55911895 |hdl-access=free |url-access=subscription }}</ref>

Recent studies have confirmed a correlation between Viluy traps in the [[Vilyuysk]] region on the [[Siberian Craton]] and the Kellwasser extinction by <sup>40</sup>Ar/<sup>39</sup>Ar dating.<ref>{{cite journal |author=Courtillot, V. |display-authors=etal |year=2010 |title=Preliminary dating of the Viluy traps (Eastern Siberia): Eruption at the time of Late Devonian extinction events? |journal=Earth and Planetary Science Letters |volume=102 |issue=1–2 |pages=29–59 |bibcode=2010ESRv..102...29K |doi=10.1016/j.earscirev.2010.06.004}}</ref><ref name="Ricci-2013">{{cite journal |author=Ricci, J. |display-authors=etal |year=2013 |title=New <sup>40</sup>Ar/<sup>39</sup>Ar and K–Ar ages of the Viluy traps (Eastern Siberia): Further evidence for a relationship with the Frasnian–Famennian mass extinction |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=386 |pages=531–540 |doi=10.1016/j.palaeo.2013.06.020|bibcode=2013PPP...386..531R }}</ref> Ages show{{clarify|date=September 2018}} that the two volcanic phase hypotheses are well supported and the weighted mean ages of each volcanic phase are {{val|376.7|3.4}} and {{val|364.4|3.4}}&nbsp;Ma, or {{val|373.4|2.1}} and {{val|363.2|2.0}}&nbsp;Ma, which the first volcanic phase is in agreement with the age of {{val|372.2|3.2}}&nbsp;Ma proposed for the Kellwasser event. However, the second volcanic phase is slightly older than Hangenberg event, which is dated to around {{val|358.9|1.2}}&nbsp;Ma.{{clarify|date=September 2018}}<ref name="Ricci-2013" />

[[Coronene]] and [[mercury (element)|mercury]] enrichment has been found in deposits dating back to the Kellwasser event, with similar enrichments found in deposits coeval with the Frasnes event at the Givetian-Frasnian boundary and in ones coeval with the Hangenberg event. Because coronene enrichment is only known in association with large igneous province emissions and extraterrestrial impacts and the fact that there is no confirmed evidence of the latter occurring in association with the Kellwasser event, this enrichment strongly suggests a causal relationship between volcanism and the Kellwasser extinction event.<ref>{{cite journal |last1=Kaiho |first1=Kunio |last2=Miura |first2=Mami |last3=Tezuka |first3=Mio |last4=Hayashi |first4=Naohiro |last5=Jones |first5=David S. |last6=Oikawa |first6=Kazuma |last7=Casier |first7=Jean-Georges |last8=Fujibayashi |first8=Megumu |last9=Chen |first9=Zhong-Qiang |date=April 2021 |title=Coronene, mercury, and biomarker data support a link between extinction magnitude and volcanic intensity in the Late Devonian |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818121000370 |journal=[[Global and Planetary Change]] |volume=199 |article-number=103452 |doi=10.1016/j.gloplacha.2021.103452 |bibcode=2021GPC...19903452K |s2cid=234364043 |access-date=23 December 2022|url-access=subscription }}</ref> However, not all sites show evidence of mercury enrichment across the Frasnian-Famennian boundary, leading other studies to reject volcanism as an explanation for the crisis.<ref name=":1" />

Another overlooked contributor to the Kellwasser mass extinction could be the now extinct [[Lake Eildon National Park|Cerberean Caldera]] which was active in the Late [[Devonian]] period and thought to have undergone a [[supereruption]] approximately 374 million years ago.{{refn|group=lower-alpha|Though a super eruption on its own would have devastating effects in both short term and long term, the Late Devonian extinction was caused by a series of events which contributed to the extinction.<ref>{{cite web |title=Devonian Mass Extinction: Causes, Facts, Evidence & Animals |url=https://study.com/academy/lesson/devonian-mass-extinction-causes-facts-evidence-animals.html |website=Study.com |access-date=4 October 2019 |language=en}}</ref>}}<ref name="Cerberean Caldera">{{cite journal |last1=Clemens |first1=J. D. |last2=Birch |first2=W. D. |title=Assembly of a zoned volcanic magma chamber from multiple magma batches: The Cerberean Cauldron, Marysville Igneous Complex, Australia |journal=Lithos |volume=155 |date=2012 |pages=272–288 |bibcode=2012Litho.155..272C |doi=10.1016/j.lithos.2012.09.007 }}</ref> Remains of this caldera can be found in the modern day state of Victoria, Australia. Eovariscan volcanic activity in present-day Europe may have also played a role in conjunction with the Viluy Traps.<ref>{{cite journal |last1=Racki |first1=Grzegorz |last2=Rakociński |first2=Michał |last3=Marynowski |first3=Leszek |last4=Wignall |first4=Paul B. |date=26 April 2018 |title=Mercury enrichments and the Frasnian-Famennian biotic crisis: A volcanic trigger proved? |url=https://pubs.geoscienceworld.org/gsa/geology/article/46/6/543/530692/Mercury-enrichments-and-the-Frasnian-Famennian |journal=Geology |volume=46 |issue=6 |pages=543–546 |doi=10.1130/G40233.1 |bibcode=2018Geo....46..543R |access-date=23 December 2022|url-access=subscription }}</ref><ref>{{cite journal |last1=Racki |first1=Grezgorz |date=June 2020 |title=A volcanic scenario for the Frasnian–Famennian major biotic crisis and other Late Devonian global changes: More answers than questions? |journal=[[Global and Planetary Change]] |volume=189 |article-number=103174 |doi=10.1016/j.gloplacha.2020.103174 |bibcode=2020GPC...18903174R |s2cid=216223745 |doi-access=free |hdl=20.500.12128/14061 |hdl-access=free }}</ref>

=== Impact event ===
[[Bolide]] impacts can be dramatic triggers of mass extinctions. An asteroid impact was proposed as the prime cause of this faunal turnover.<ref name="McGhee" /><ref>Digby McLaren, 1969</ref> The impact that created the [[Siljan Ring]] either was just before the Kellwasser event or coincided with it.<ref>{{cite journal |last1=Reimold |first1=Wolf U. |last2=Kelley |first2=Simon P. |last3=Sherlock |first3=Sarah C. |last4=Henkel |first4=Herbert |last5=Koeberl |first5=Christian |date=26 January 2010 |title=Laser argon dating of melt breccias from the Siljan impact structure, Sweden: Implications for a possible relationship to Late Devonian extinction events |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1945-5100.2005.tb00965.x |journal=[[Meteoritics & Planetary Science]] |volume=40 |issue=4 |pages=591–607 |doi=10.1111/j.1945-5100.2005.tb00965.x |s2cid=23316812 |access-date=14 January 2023|url-access=subscription }}</ref><ref>J.R. Morrow and C.A. Sandberg. [http://www.lpi.usra.edu/meetings/metsoc2005/pdf/5148.pdf Revised Dating Of Alamo And Some Other Late Devonian Impacts In Relation To Resulting Mass Extinction], 68th Annual Meteoritical Society Meeting (2005)</ref> Most impact craters, such as the Kellwasser-aged [[Alamo bolide impact|Alamo]], cannot generally be dated with sufficient precision to link them to the event; others dated precisely are not contemporaneous with the extinction.<ref name="Racki, 2005" /> Although some evidence of meteoric impact have been observed in places, including iridium anomalies<ref>{{cite journal |last1=Becker |first1=R. Thomas |last2=House |first2=Michael R. |last3=Kirchgasser |first3=William T. |last4=Playford |first4=Phillip E. |date=1991 |title=Sedimentary and faunal changes across the frasnian/famennian boundary in the canning basin of Western Australia |url=https://www.tandfonline.com/doi/abs/10.1080/10292389109380400 |journal=[[Historical Biology]] |volume=5 |issue=2–4 |pages=183–196 |doi=10.1080/10292389109380400 |bibcode=1991HBio....5..183B |access-date=15 January 2023|url-access=subscription }}</ref> and microspherules,<ref>{{cite journal |last1=Claeys |first1=Philippe |last2=Casier |first2=Jean-Georges |date=April 1994 |title=Microtektite-like impact glass associated with the Frasnian-Famennian boundary mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/0012821X94900043 |journal=[[Earth and Planetary Science Letters]] |volume=122 |issue=3–4 |pages=303–315 |doi=10.1016/0012-821X(94)90004-3 |bibcode=1994E&PSL.122..303C |access-date=15 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Claeys |first1=Philippe |last2=Casier |first2=Jean-Georges |last3=Margolis |first3=Stanley V. |date=21 August 1992 |title=Microtektites and Mass Extinctions: Evidence for a Late Devonian Asteroid Impact |url=https://www.science.org/doi/abs/10.1126/science.257.5073.1102 |journal=[[Science (journal)|Science]] |volume=257 |issue=5073 |pages=1102–1104 |doi=10.1126/science.257.5073.1102 |pmid=17840279 |bibcode=1992Sci...257.1102C |s2cid=40588088 |access-date=15 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Claeys |first1=P. |last2=Kyte |first2=F. T. |last3=Herbosch |first3=A. |last4=Casier |first4=J.-G. |date=1 January 1996 |title=Geochemistry of the Frasnian-Famennian boundary in Belgium: Mass extinction, anoxic oceans and microtektite layer, but not much iridium? |url=https://researchportal.vub.be/en/publications/geochemistry-of-the-frasnian-famennian-boundary-in-belgium-mass-e |journal=Special Paper of the Geological Society of America |volume=307 |pages=491–506 |doi=10.1130/0-8137-2307-8.491 |isbn=978-0-8137-2307-5 |access-date=26 January 2023|url-access=subscription }}</ref> these were probably caused by other factors.<ref name="Algeo1995" /><ref>{{cite journal |vauthors=Wang K, Attrep M, Orth CJ |date=December 2017 |title=Global iridium anomaly, mass extinction, and redox change at the Devonian-Carboniferous boundary |journal=[[Geology (journal)|Geology]] |volume=21 |issue=12 |pages=1071–1074 |doi=10.1130/0091-7613(1993)021<1071:giamea>2.3.co;2}}</ref><ref>{{cite journal |last1=Nicoll |first1=Robert S. |last2=Playford |first2=Phillip E. |date=September 1993 |title=Upper Devonian iridium anomalies, conodont zonation and the Frasnian-Famennian boundary in the Canning Basin, Western Australia |url=https://www.sciencedirect.com/science/article/abs/pii/003101829390123Z |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=104 |issue=1–4 |pages=105–113 |doi=10.1016/0031-0182(93)90123-Z |bibcode=1993PPP...104..105N |access-date=15 January 2023|url-access=subscription }}</ref> Some lines of evidence suggest that the meteorite impact and its associated geochemical signals postdate the extinction event.<ref>{{cite journal |last1=McGhee Jr. |first1=George R. |last2=Orth |first2=Charles J. |last3=Quintana |first3=Leonard R. |last4=Gilmore |first4=James S. |last5=Olsen |first5=Edward J. |date=1 September 1986 |title=Late Devonian "Kellwasser Event" mass-extinction horizon in Germany: No geochemical evidence for a large-body impact |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/14/9/776/204148/Late-Devonian-Kellwasser-Event-mass-extinction |journal=[[Geology (journal)|Geology]] |volume=14 |issue=9 |pages=776–779 |doi=10.1130/0091-7613(1986)14<776:LDKEMH>2.0.CO;2 |bibcode=1986Geo....14..776M |access-date=19 April 2023|url-access=subscription }}</ref> Modelling studies have ruled out a single impact as entirely inconsistent with available evidence, although a multiple impact scenario may still be viable.<ref>{{cite book |last1=McGhee Jr. |first1=George R. |editor-last1=Over |editor-first1=D. J. |editor-last2=Morrow |editor-first2=J. R. |editor-last3=Wignall |editor-first3=Paul B. |date=2005 |title=Understanding Late Devonian And Permian-Triassic Biotic and Climatic Events: Towards an Integrated Approach |url=https://www.sciencedirect.com/bookseries/developments-in-palaeontology-and-stratigraphy/vol/20/suppl/C |chapter=Modelling Late Devonian Extinction Hypotheses |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/S0920544605800032 |volume=20 |publisher=[[Elsevier]] |pages=37–50 |doi=10.1016/S0920-5446(05)80003-2 |isbn=978-0-444-52127-9 |access-date=11 November 2023}}</ref>

=== Supernova ===
[[Near-Earth supernova|Near-Earth supernovae]] have been speculated as possible drivers of mass extinctions due to their ability to cause [[ozone depletion]].<ref>{{Cite journal |last1=Brunton |first1=Ian R. |last2=O'Mahoney |first2=Connor |last3=Fields |first3=Brian D. |last4=Melott |first4=Adrian L. |last5=Thomas |first5=Brian C. |date=19 April 2023 |title=X-Ray-luminous Supernovae: Threats to Terrestrial Biospheres |journal=[[The Astrophysical Journal]] |volume=947 |issue=2 |page=42 |doi=10.3847/1538-4357/acc728 |issn=0004-637X |doi-access=free |arxiv=2210.11622 |bibcode=2023ApJ...947...42B }}</ref> A recent explanation suggests that a nearby [[supernova]] explosion was the cause for the specific [[Hangenberg event]], which marks the boundary between the Devonian and Carboniferous periods. This could offer a possible explanation for the dramatic drop in atmospheric ozone during the Hangenberg event that could have permitted massive ultraviolet damage to the genetic material of lifeforms, triggering a mass extinction. Recent research offers evidence of ultraviolet damage to pollen and spores over many thousands of years during this event as observed in the fossil record and that, in turn, points to a possible long-term destruction of the ozone layer. A supernova explosion is an alternative explanation to global temperature rise, that could account for the drop in atmospheric ozone. Because very high mass stars, required to produce a supernova, tend to form in dense star-forming regions of space and have short lifespans lasting only at most tens of millions of years, it is likely that if a supernova did occur, multiple others also did within a few million years of it. Thus, supernovae have also been speculated to have been responsible for the Kellwasser event, as well as the entire sequence of environmental crises covering several millions of years towards the end of the Devonian period. Detecting either of the long-lived, extra-terrestrial radioisotopes [[samarium-146|<sup>146</sup>Sm]] or [[plutonium-244|<sup>244</sup>Pu]] in one or more end-Devonian extinction strata would confirm a supernova origin. However, there is currently no direct evidence for this hypothesis.<ref name="Fields-2020">{{Cite journal |last1=Fields |first1=Brian D. |last2=Melott |first2=Adrian L. |last3=Ellis |first3=John |last4=Ertel |first4=Adrienne F. |last5=Fry |first5=Brian J. |last6=Lieberman |first6=Bruce S. |last7=Liu |first7=Zhenghai |last8=Miller |first8=Jesse A. |last9=Thomas |first9=Brian C. |date=2020-08-18 |title=Supernova triggers for end-Devonian extinctions |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |language=en |volume=117 |issue=35 |pages=21008–21010 |arxiv=2007.01887 |bibcode=2020PNAS..11721008F |doi=10.1073/pnas.2013774117 |issn=0027-8424 |pmc=7474607 |pmid=32817482 |doi-access=free}}</ref>

=== Other hypotheses ===

Other mechanisms put forward to explain the extinctions include [[tectonic]]-driven [[Climate change (general concept)|climate change]], sea-level change, and oceanic overturning.<ref>{{cite journal |last1=Racki |first1=Grzegorz |date=September 1998 |title=Frasnian–Famennian biotic crisis: undervalued tectonic control? |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018298000595 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=141 |issue=3–4 |pages=177–198 |doi=10.1016/S0031-0182(98)00059-5 |bibcode=1998PPP...141..177R |access-date=26 January 2023|url-access=subscription }}</ref><ref>{{cite book |last1=Stock |first1=Carl W. |editor-last1=Over |editor-first1=D. J. |editor-last2=Morrow |editor-first2=J. R. |editor-last3=Wignall |editor-first3=Paul B. |date=2005 |title=Understanding Late Devonian And Permian-Triassic Biotic and Climatic Events: Towards an Integrated Approach |url=https://www.sciencedirect.com/bookseries/developments-in-palaeontology-and-stratigraphy/vol/20/suppl/C |chapter=Devonian stromatoporoid originations, extinctions, and paleobiogeography: how they relate to the Frasnian-Famennian extinction |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/S0920544605800056 |volume=20 |publisher=[[Elsevier]] |pages=71–92 |doi=10.1016/S0920-5446(05)80005-6 |isbn=978-0-444-52127-9 |access-date=11 November 2023}}</ref> These have all been discounted because they are unable to explain the duration, selectivity, and periodicity of the extinctions.<ref>{{cite journal |last1=Kabanov |first1=P. |last2=Jiang |first2=C. |date=May 2020 |title=Photic-zone euxinia and anoxic events in a Middle-Late Devonian shelfal sea of Panthalassan continental margin, NW Canada: Changing paradigm of Devonian ocean and sea level fluctuations |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818120300436 |journal=[[Global and Planetary Change]] |volume=188 |article-number=103153 |doi=10.1016/j.gloplacha.2020.103153 |bibcode=2020GPC...18803153K |s2cid=216294884 |access-date=26 January 2023|url-access=subscription }}</ref><ref name="Algeo1995" />

==See also==
* [[Evolutionary history of plants]]

==Notes==
{{Reflist|group=lower-alpha}}

==References==
{{Reflist|2}}

==Sources==
* {{Cite book |last=McGhee |first=George R. |url=https://books.google.com/books?id=xc70cveVCJsC&pg=PA9 |title=The late Devonian mass extinction: the Frasnian Famennian crisis |date=1996 |publisher=[[Columbia University Press]] |isbn=978-0-231-07505-3 |series=Critical moments in paleobiology and earth history series |location=New York |page=9 |access-date=23 July 2015}}
* {{Cite book |last=Racki |first=Grzegorz |title=Understanding Late Devonian and Permian-Triassic biotic and climate events: towards an integrated approach |date=2005 |publisher=[[Elsevier]] |isbn=978-0-444-52127-9 |editor-last=Over |editor-first=D. Jeffrey |edition=1. |series=Developments in palaeontology and stratigraphy |location=Amsterdam |chapter=Toward understanding Late Devonian global events: few answers, many questions}}

==External links==
* [http://www.devoniantimes.org/opportunity/massExtinction.html Late Devonian mass extinctions] {{Webarchive|url=https://web.archive.org/web/20200727171744/http://www.devoniantimes.org/opportunity/massExtinction.html |date=2020-07-27 }} at The Devonian Times. An excellent overview.
* [https://web.archive.org/web/20061028130757/http://hannover.park.org/Canada/Museum/extinction/devmass.html Devonian Mass Extinction]
* [https://www.bbc.co.uk/education/darwin/exfiles/devonian.htm BBC "The Extinction files"] "The Late Devonian Extinction"
* "[http://gsa.confex.com/gsa/2003AM/finalprogram/session_8723.htm Understanding Late Devonian and Permian-Triassic Biotic and Climatic Events: Towards an Integrated Approach] {{Webarchive|url=https://web.archive.org/web/20190408061505/http://gsa.confex.com/gsa/2003AM/finalprogram/session_8723.htm |date=2019-04-08 }}": a [[Geological Society of America]] conference in 2003 reflects current approaches
* [https://www.pbs.org/wgbh/evolution/change/deeptime/devonian.html PBS: Deep Time] 
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[[Category:Late Devonian extinctions| ]]
[[Category:Extinction events]]
[[Category:History of climate variability and change]]