Olenekian#Smithian–Spathian boundary event

The Olenekian Stage was introduced into scientific literature by Russian stratigraphers in 1956.Kiparisova & Popov (1956) The stage is named after Olenëk in Siberia. Before the subdivision in Olenekian and Induan became established, both stages formed the Scythian Stage, which has since disappeared from the official timescale.

The base of the Olenekian is at the lowest occurrence of the ammonoids Hedenstroemia or Meekoceras gracilitatis, and of the conodont Neospathodus waageni. It is defined as ending near the lowest occurrences of genera Japonites, Paradanubites, and Paracrochordiceras; and of the conodont Chiosella timorensis. A GSSP (global reference profile for the base) has not been established as of December 2020.

In the 1960s, English paleontologist Edward T. Tozer (sometimes collaborating with American geologist Norman J. Silberling) crafted Triassic timescales based on North American ammonoid zones, further refining it in the following decades. Tozer's nomenclature was largely derived from Mojsisovics's work, who coined most of the Triassic stages and substages, but he redefined them using North American sites. He recommended the Lower Triassic series be divided into the Griesbachian, Dienerian, Smithian, and Spathian. The latter two roughly correspond with the Olenekian. Tozer's timescale became popular in the Americas.{{cite journal |last=Lucas |first=S. G. |year=2010 |title=The Triassic chronostratigraphic scale: history and status |journal=Geological Society, London, Special Publications |volume=334 |issue=1 |pages=17–39 |doi=10.1144/sp334.2 |bibcode=2010GSLSP.334...17L }} He named the Smithian after Smith Creek on Ellesmere Island, Canada (the creek itself is named after geologist J. P. Smith). The Smithian is defined by the Arctoceras bloomstrandi ammonoid zone (contains Euflemingites romunderi and Juvenites crassus) and the overlying Meekoceras gracilitatis and Wasatchites tardus subzones. He named the Spathian after Spath Creek on Ellesmere Island (this creek is named after geologist L. F. Spath), and defined it by the Procolumbites subrobustus ammonoid zone.

{{See also|:Category:Olenekian life}}

Life was still recovering from the severe end-Permian mass extinction. During the Olenekian, the flora changed from lycopod dominated (e.g. Pleuromeia) to gymnosperm and pteridophyte dominated.{{cite journal |last1=Schneebeli-Hermann |first1=Elke |last2=Kürschner |first2=Wolfram M. |last3=Kerp |first3=Hans |last4=Bomfleur |first4=Benjamin |last5=Hochuli |first5=Peter A. |last6=Bucher |first6=Hugo |last7=Ware |first7=David |last8=Roohi |first8=Ghazala |title=Vegetation history across the Permian–Triassic boundary in Pakistan (Amb section, Salt Range) |journal=Gondwana Research |date=April 2015 |volume=27 |issue=3 |pages=911–924 |doi=10.1016/j.gr.2013.11.007 |bibcode=2015GondR..27..911S |url=http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-1602 }}{{cite journal |last1=Goudemand |first1=Nicolas |last2=Romano |first2=Carlo |last3=Leu |first3=Marc |last4=Bucher |first4=Hugo |last5=Trotter |first5=Julie A. |last6=Williams |first6=Ian S. |title=Dynamic interplay between climate and marine biodiversity upheavals during the early Triassic Smithian -Spathian biotic crisis |journal=Earth-Science Reviews |date=August 2019 |volume=195 |pages=169–178 |doi=10.1016/j.earscirev.2019.01.013 |bibcode=2019ESRv..195..169G |doi-access=free }} These vegetation changes are due to global changes in temperature and precipitation. Conifers (gymnosperms) were the dominant plants during most of the Mesozoic. Among land vertebrates, the archosaurs - a group of diapsid reptiles encompassing crocodiles, pterosaurs, dinosaurs, and ultimately birds - first evolved from archosauriform ancestors during the Olenekian. This group includes ferocious predators like Erythrosuchus.

In the oceans, microbial reefs were common during the Early Triassic, possibly due to lack of competition with metazoan reef builders as a result of the extinction.{{cite journal |last1=Foster |first1=William J. |last2=Heindel |first2=Katrin |last3=Richoz |first3=Sylvain |last4=Gliwa |first4=Jana |last5=Lehrmann |first5=Daniel J. |last6=Baud |first6=Aymon |last7=Kolar-Jurkovšek |first7=Tea |last8=Aljinović |first8=Dunja |last9=Jurkovšek |first9=Bogdan |last10=Korn |first10=Dieter |last11=Martindale |first11=Rowan C. |last12=Peckmann |first12=Jörn |title=Suppressed competitive exclusion enabled the proliferation of Permian/Triassic boundary microbialites |journal=The Depositional Record |date=20 November 2019 |volume=6 |issue=1 |pages=62–74 |doi=10.1002/dep2.97 |pmid=32140241 |pmc=7043383 }} However, transient metazoan reefs reoccurred during the Olenekian wherever permitted by environmental conditions.{{cite journal |last1=Brayard |first1=Arnaud |last2=Vennin |first2=Emmanuelle |last3=Olivier |first3=Nicolas |last4=Bylund |first4=Kevin G. |last5=Jenks |first5=Jim |last6=Stephen |first6=Daniel A. |last7=Bucher |first7=Hugo |last8=Hofmann |first8=Richard |last9=Goudemand |first9=Nicolas |last10=Escarguel |first10=Gilles |title=Transient metazoan reefs in the aftermath of the end-Permian mass extinction |journal=Nature Geoscience |date=18 September 2011 |volume=4 |issue=10 |pages=693–697 |doi=10.1038/ngeo1264 |bibcode=2011NatGe...4..693B }} Ammonoids and conodonts diversified, but both suffered losses during the Smithian-Spathian boundary extinction (see below){{cite journal |last1=Galfetti |first1=Thomas |last2=Hochuli |first2=Peter A. |last3=Brayard |first3=Arnaud |last4=Bucher |first4=Hugo |last5=Weissert |first5=Helmut |last6=Vigran |first6=Jorunn Os |title=Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis |journal=Geology |date=2007 |volume=35 |issue=4 |pages=291 |doi=10.1130/G23117A.1 |bibcode=2007Geo....35..291G }} at the end of the Smithian subage.

Ray-finned fishes largely remained unaffected by the Permian-Triassic extinction event. Coelacanths show their highest post-Devonian diversity during the Early Triassic.{{cite journal |last1=Romano |first1=Carlo |last2=Koot |first2=Martha B. |last3=Kogan |first3=Ilja |last4=Brayard |first4=Arnaud |last5=Minikh |first5=Alla V. |last6=Brinkmann |first6=Winand |last7=Bucher |first7=Hugo |last8=Kriwet |first8=Jürgen |title=Permian-Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution |journal=Biological Reviews |date=February 2016 |volume=91 |issue=1 |pages=106–147 |doi=10.1111/brv.12161 |pmid=25431138 |url=https://hal.science/hal-01253154/file/Romano_et_al_HAL.pdf }}{{cite journal |last1=Smithwick |first1=Fiann M. |last2=Stubbs |first2=Thomas L. |title=Phanerozoic survivors: Actinopterygian evolution through the Permo-Triassic and Triassic-Jurassic mass extinction events |journal=Evolution |date=2 February 2018 |volume=72 |issue=2 |pages=348–362 |doi=10.1111/evo.13421 |pmid=29315531 |pmc=5817399 |doi-access=free }} Many fish genera show a cosmopolitan distribution during the Induan and Olenekian, such as Australosomus, Birgeria, Parasemionotidae, Pteronisculus, Ptycholepidae, Saurichthys and Whiteia. This is well exemplified in the Griesbachian (early Induan) aged fish assemblages of the Wordie Creek Formation (East Greenland),{{cite journal |first=Erik |last=Stensiö |author-link=Erik Stensiö |year=1932 |title=Triassic Fishes from East Greenland collected by the Danish expeditions in 1929-1931 |journal=Meddelelser om Grønland |volume=83 |issue=3 |pages=1–305 |oclc=938169014 }}{{cite journal |last=Nielsen |first=Eigil |author-link=Eigil Nielsen (paleontologist) |year=1936 |title=Some few preliminary remarks on Triassic fishes from East Greenland |journal=Meddelelser om Grønland |volume=112 |issue=3 |pages=1–55}} the Dienerian (late Induan) aged assemblages of the Middle Sakamena Formation (Madagascar),{{cite book |last=Beltan |first=Laurence |year=1996 |chapter=Overview of systematics, paleobiology, and paleoecology of Triassic fishes of northwestern Madagascar |editor1=G. Arratia |editor2=G. Viohl |title=Mesozoic Fishes—Systematics and Paleoecology |pages=479–500 |publisher=Dr. Friedrich Pfeil |location=München}} Candelaria Formation (Nevada, United States),{{cite journal |last1=Romano |first1=Carlo |last2=López-Arbarello |first2=Adriana |last3=Ware |first3=David |last4=Jenks |first4=James F. |last5=Brinkmann |first5=Winand |title=Marine Early Triassic Actinopterygii from the Candelaria Hills (Esmeralda County, Nevada, USA) |journal=Journal of Paleontology |date=April 2019 |volume=93 |issue=5 |pages=971–1000 |doi=10.1017/jpa.2019.18|bibcode=2019JPal...93..971R }} and Mikin Formation (Himachal Pradesh, India),{{cite journal |last1=Romano |first1=Carlo |last2=Ware |first2=David |last3=Brühwiler |first3=Thomas |last4=Bucher |first4=Hugo |last5=Brinkmann |first5=Winand |title=Marine Early Triassic Osteichthyes from Spiti, Indian Himalayas |journal=Swiss Journal of Palaeontology |date=2016 |volume=135 |issue=2 |pages=275–294 |doi=10.1007/s13358-015-0098-6 |bibcode=2016SwJP..135..275R |doi-access=free}} and Daye Formation (Guizhou, China),{{Cite journal|last1=Dai |first1=X. |last2=Davies |first2=J. H. F. L. |last3=Yuan |first3=Z. |last4=Brayard |first4=A. |last5=Ovtcharova |first5=M. |last6=Xu |first6=G. |last7=Liu |first7=X. |last8=Smith |first8=C. P. A. |last9=Schweitzer |first9=C. E. |last10=Li |first10=M. |last11=Perrot |first11=M. G. |last12=Jiang |first12=S. |last13=Miao |first13=L. |last14=Cao |first14=Y. |last15=Yan |first15=J. |last16=Bai |first16=R. |last17=Wang |first17=F. |last18=Guo |first18=W. |last19=Song |first19=H. |last20=Tian |first20=L. |last21=Dal Corso |first21=J. |last22=Liu |first22=Y. |last23=Chu |first23=D. |last24=Song |first24=H. |title=A Mesozoic fossil lagerstätte from 250.8 million years ago shows a modern-type marine ecosystem |year=2023 |journal=Science |volume=379 |issue=6632 |pages=567–572 |doi=10.1126/science.adf1622 |pmid=36758082 |bibcode=2023Sci...379..567D |url=https://u-bourgogne.hal.science/hal-04016004/file/Dai%20et%20al.%20MS%20Version%20HAL.pdf }} and the Smithian aged assemblages of the Vikinghøgda Formation (Spitsbergen, Norway),{{cite book |last=Stensiö |first=E. |author-link=Erik Stensiö |year=1921 |title=Triassic fishes from Spitzbergen 1 |pages=xxviii+307 |publisher=Adolf Holzhausen |location=Wien}}{{cite journal |last=Stensiö |first=E. |author-link=Erik Stensiö |year=1925 |title=Triassic fishes from Spitzbergen 2 |journal=Kungliga Svenska Vetenskapsakademiens Handlingar |volume=3 |pages=1–261}}{{cite journal |last1=Kogan |first1=Ilja |last2=Romano |first2=Carlo |title=A new postcranium of Saurichthys from the Early Triassic of Spitsbergen |journal=Freiberger Forschungshefte, Reihe C |date=2016 |pages=205–222 |doi=10.5167/uzh-136748 }} and Thaynes Group (western United States),{{cite journal |author=Romano C., Kogan I., Jenks J., Jerjen I., Brinkmann W. |year=2012 |title=Saurichthys and other fossil fishes from the late Smithian (Early Triassic) of Bear Lake County (Idaho, USA), with a discussion of saurichthyid palaeogeography and evolution |url=http://www.geology.cz/bulletin/fulltext/1337_Romano.pdf |journal=Bulletin of Geosciences |volume=87 |pages=543–570 |doi=10.3140/bull.geosci.1337 }} and Helongshan Formation (Anhui, China),{{cite journal|last1=Tong |first1=Jinnan |last2=Zhou |first2=Xiugao |last3=Erwin |first3=Douglas H. |last4=Zuo |first4=Jingxun |last5=Zhao |first5=Laishi |year=2006 |title=Fossil fishes from the Lower Triassic of Majiashan, Chaohu, Anhui Province, China |journal=Journal of Paleontology |volume=80 |issue=1 |pages=146–161 |doi=10.1666/0022-3360(2006)080[0146:FFFTLT]2.0.CO;2 }} and several Early Triassic layers of the Sulphur Mountain Formation (western Canada).{{cite journal |last1=Schaeffer |first1=Bobb |last2=Mangus |first2=Marlyn |title=An Early Triassic fish assemblage from British Columbia |journal=Bulletin of the American Museum of Natural History |volume=156 |issue=5 |pages=516–563 |year=1976 |hdl=2246/619 |url=http://digitallibrary.amnh.org/handle/2246/619 }} Ray-finned fishes diversified after the mass extinction and reached peak diversity during the Middle Triassic. This diversification is, however, obscured by a taphonomic megabias (Spathian-Bithynian Gap, SBG){{cite journal |last1=Romano |first1=Carlo |title=A Hiatus Obscures the Early Evolution of Modern Lineages of Bony Fishes |journal=Frontiers in Earth Science |date=January 2021 |volume=8 |pages=618853 |doi=10.3389/feart.2020.618853|doi-access=free |bibcode=2021FrEaS...8.8853R }} during the late Olenekian and early middle Anisian. The earliest large durophagous neopterygian is known from the SBG, suggesting an early onset of the Triassic actinopterygian revolution.{{Cite journal|last1=Cavin |first1=L. |last2=Argyriou |first2=T. |last3=Romano |first3=C. |last4=Grădinaru |first4=E. |year=2024 |title=Large durophagous fish from the Spathian (late Early Triassic) of Romania hints at earlier onset of the Triassic actinopterygian revolution |journal=Papers in Palaeontology |volume=10 |issue=2 |at=e1553 |doi=10.1002/spp2.1553 |bibcode=2024PPal...10E1553C }}

Olenekian chondrichthyan fishes include hybodonts and neoselachians,{{cite journal |last1=Romano |first1=Carlo |last2=Brinkmann |first2=Winand |title=A new specimen of the hybodont shark Palaeobates polaris with threedimensionally preserved Meckel's cartilage from the Smithian (Early Triassic) of Spitsbergen |journal=Journal of Vertebrate Paleontology |date=December 2010 |volume=30 |issue=6 |pages=1673–1683 |doi=10.1080/02724634.2010.521962 |bibcode=2010JVPal..30.1673R }}{{Cite journal |last1=Bratvold |first1=Janne |last2=Delsett |first2=Lene Liebe |last3=Hurum |first3=Jørn Harald |date=2018-10-04 |title=Chondrichthyans from the Grippia bonebed (Early Triassic) of Marmierfjellet, Spitsbergen |journal=Norwegian Journal of Geology |volume=98 |issue=2 |pages=189–217 |doi=10.17850/njg98-2-03 |hdl=10852/71103 |hdl-access=free }} but also a few surviving lineages of eugeneodontid holocephalians,{{cite book |last1=Mutter |first1=Raoul J. |last2=Neuman |first2=Andrew G. |year=2008 |chapter=New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada |title=Fishes and the Break-up of Pangaea |editor1=Cavin, L. |editor2=Longbottom, A. |editor3=Richter, M. |series=Geological Society of London, Special Publications |publisher=Geological Society of London |location=London |volume=295 |pages=9–41 |doi=10.1144/sp295.3 }} a mainly Palaeozoic group that went extinct during the Early Triassic.

Marine temnospondyl amphibians, such as the superficially crocodile-shaped trematosaurids Aphaneramma and Wantzosaurus, show wide geographic ranges during the Induan and Olenekian ages. Their fossils are found in Greenland, Spitsbergen, Pakistan and Madagascar.{{cite journal |last1=Scheyer |first1=Torsten M. |last2=Romano |first2=Carlo |last3=Jenks |first3=Jim |last4=Bucher |first4=Hugo |last5=Farke |first5=Andrew A. |title=Early Triassic Marine Biotic Recovery: The Predators' Perspective |journal=PLOS ONE |date=19 March 2014 |volume=9 |issue=3 |pages=e88987 |doi=10.1371/journal.pone.0088987 |pmid=24647136 |pmc=3960099 |bibcode=2014PLoSO...988987S |doi-access=free }} Others, such as Trematosaurus, inhabited freshwater environments and were less widespread.

The first marine reptiles appeared during the Olenekian. Hupehsuchia, Ichthyopterygia and Sauropterygia are among the first marine reptiles to enter the scene (e.g. Cartorhynchus, Chaohusaurus, Utatsusaurus, Hupehsuchus, Grippia, Omphalosaurus, Corosaurus). Sauropterygians and ichthyosaurs ruled the oceans during the Mesozoic Era.

An example of an exceptionally diverse Early Triassic assemblage is the Paris biota, fossils of which were discovered near Paris, Idaho{{cite journal |last1=Brayard |first1=Arnaud |last2=Krumenacker |first2=L. J. |last3=Botting |first3=Joseph P. |last4=Jenks |first4=James F. |last5=Bylund |first5=Kevin G. |last6=Fara |first6=Emmanuel |last7=Vennin |first7=Emmanuelle |last8=Olivier |first8=Nicolas |last9=Goudemand |first9=Nicolas |last10=Saucède |first10=Thomas |last11=Charbonnier |first11=Sylvain |last12=Romano |first12=Carlo |last13=Doguzhaeva |first13=Larisa |last14=Thuy |first14=Ben |last15=Hautmann |first15=Michael |last16=Stephen |first16=Daniel A. |last17=Thomazo |first17=Christophe |last18=Escarguel |first18=Gilles |title=Unexpected Early Triassic marine ecosystem and the rise of the Modern evolutionary fauna |journal=Science Advances |date=15 February 2017 |volume=3 |issue=2 |pages=e1602159 |doi=10.1126/sciadv.1602159 |pmid=28246643 |pmc=5310825 |bibcode=2017SciA....3E2159B |doi-access=free }} and other nearby sites in Idaho and Nevada.{{cite journal| last1 = Smith| first1 = Christopher P.A. | last2 = Laville | first2 = Thomas | last3 = Fara | first3 = Emmauel | last4 = Escarguel | first4 = Gilles | last5 = Olivier | first5 = Nicolas | last6 = Vennin | first6 = Emmanuelle | last7 = Goudemand | first7 = Nicolas | last8 = Bylund | first8 = Kevin G. | last9 = Jenks| first9 = James F. | last10 = Stephen | first10 = Daniel A. | last11 = Hautmann | first11 = Michael | last12 = Charbonnier | first12 = Sylvain | last13 = Krumenacker | first13 = L. J. | last14 = Brayard | first14 = Arnaud | title = Exceptional fossil assemblages confirm the existence of complex Early Triassic ecosystems during the early Spathian | journal = Scientific Reports | volume = 11 | pages = 19657 | date = 4 October 2021 | issue = 1 | pmid=34608207|doi = 10.1038/s41598-021-99056-8 | pmc = 8490361 | bibcode = 2021NatSR..1119657S }} The Paris Biota was deposited in the wake of the SSBM and it features at least 7 phyla and 20 distinct metazoan orders, including leptomitid protomonaxonid sponges (previously only known from the Paleozoic), thylacocephalans, crustaceans, nautiloids, ammonoids, coleoids, ophiuroids, crinoids, and vertebrates.{{cite journal |last1=Iniesto |first1=Miguel |last2=Thomazo |first2=Christophe |last3=Fara |first3=Emmanuel |title=Deciphering the exceptional preservation of the Early Triassic Paris Biota (Bear Lake County, Idaho, USA) |journal=Geobios |date=June 2019 |volume=54 |pages=81–93 |doi=10.1016/j.geobios.2019.04.002 }} Such diverse assemblages show that organisms diversified wherever and whenever climatic and environmental conditions ameliorated.

{{gallery|File:Pleuromeia_restoration.png|Life restoration of Pleuromeia, a genus of lycophyte that was globally abundant during the Olenekinian|File:Birgeria_americana_white_background.jpg|Skull of the ray-finned fish Birgeria americana|Trematosaurus_brauni.JPG|Skull of the temnospondyl amphibian Trematosaurus brauni|File:Erythrosuchus_africanus_34.jpg|Skull of the archosauriform reptile Erythrosuchus africanus|File:Chaohusaurus_AGM_CH-628-22.png|Marine ichthyosauromorph reptile Chaohusaurus}}

File:Triassic_marine_vertebrate_apex_predators.png, 2. Fadenia, 3. Saurichthys, 4. Rebellatrix, 5. Hovasaurus, 6. Birgeria, 7. Aphaneramma, 8. Bobasatrania, 9. Hybodontiformes, 10. Mylacanthus, 11. Tanystropheus, 12. Corosaurus, 13. Ticinepomis, 14. Mixosaurus, 15. Cymbospondylidae, 16. Neoselachii, 17. Omphalosaurus skeleton, 18. Placodus]]

An important extinction event occurred during the Olenekian age of the Early Triassic, near the subage boundary between the Smithian and Spathian. The main victims of this Smithian–Spathian boundary event, often called the Smithian–Spathian extinction,{{cite journal |last1=Galfetti |first1=Thomas |last2=Hochuli |first2=Peter A. |last3=Brayard |first3=Arnaud |last4=Bucher |first4=Hugo |last5=Weissert |first5=Helmut |last6=Vigran |first6=Jorunn Os |date=2007 |title=Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis |journal=Geology |volume=35 |issue=4 |pages=291 |bibcode=2007Geo....35..291G |doi=10.1130/G23117A.1}} were the Palaeozoic disaster taxa that survived the Permian–Triassic extinction event and flourished in the newly vacated niches during immediate aftermath of the Great Death;{{cite journal |last1=Sun |first1=Y. D. |last2=Wignall |first2=Paul B. |last3=Joachimski |first3=M. M. |last4=Bond |first4=David P. G. |last5=Grasby |first5=S. E. |last6=Sun |first6=S. |last7=Yan |first7=C. B. |last8=Wang |first8=L. N. |last9=Chen |first9=Y. L. |last10=Lai |first10=X. L. |date=1 June 2015 |title=High amplitude redox changes in the late Early Triassic of South China and the Smithian–Spathian extinction |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=427 |pages=62–78 |doi=10.1016/j.palaeo.2015.03.038 |bibcode=2015PPP...427...62S |url=https://hull-repository.worktribe.com/file/373664/1/Article }} ammonoids, conodonts and radiolarians in particular suffered drastic biodiversity losses,{{cite journal |last1=Zhang |first1=Lei |last2=Orchard |first2=Michael J. |last3=Brayard |first3=Arnaud |last4=Algeo |first4=Thomas J. |last5=Zhao |first5=Laishi |last6=Chen |first6=Zhong-Qiang |last7=Lyu |first7=Zhengyi |date=August 2019 |title=The Smithian/Spathian boundary (late Early Triassic): A review of ammonoid, conodont, and carbon-isotopic criteria |journal=Earth-Science Reviews |volume=195 |pages=7–36 |doi=10.1016/j.earscirev.2019.02.014 |bibcode=2019ESRv..195....7Z }} which is accentuated, among others, by the cosmopolitan distribution of the ammonoid Anasibirites.{{Cite journal |last1=Jattiot |first1=Romain |last2=Bucher |first2=Hugo |last3=Brayard |first3=Arnaud |last4=Monnet |first4=Claude |last5=Jenks |first5=James F. |last6=Hautmann |first6=Michael |year=2016 |title=Revision of the genus Anasibirites Mojsisovics (Ammonoidea): An iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction |journal=Papers in Palaeontology |volume=2 |issue=1 |pages=155–188 |doi=10.1002/spp2.1036 |bibcode=2016PPal....2..155J |url=https://hal.science/hal-01282981/document |doi-access=free |hdl=20.500.12210/34589 |hdl-access=free }} Marine reptiles, such as ichthyopterygians and sauropterygians, diversified after the extinction.

The terrestrial flora was also affected significantly, changing from lycopod-dominated (e.g. Pleuromeia) during the Dienerian and Smithian subages to gymnosperm- and pteridophyte-dominated in the Spathian.{{cite journal |last1=Schneebeli-Hermann |first1=Elke |last2=Kürschner |first2=Wolfram M. |last3=Kerp |first3=Hans |last4=Bomfleur |first4=Benjamin |last5=Hochuli |first5=Peter A. |last6=Bucher |first6=Hugo |last7=Ware |first7=David |last8=Roohi |first8=Ghazala |date=April 2015 |title=Vegetation history across the Permian–Triassic boundary in Pakistan (Amb section, Salt Range) |journal=Gondwana Research |volume=27 |issue=3 |pages=911–924 |bibcode=2015GondR..27..911S |doi=10.1016/j.gr.2013.11.007 |url=http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-1602 }} These vegetation changes are due to global changes in temperature and precipitation. Conifers (gymnosperms) were the dominant plants during most of the Mesozoic. Until recently{{when|date=October 2022}} the existence of this extinction event about 249.4 Ma ago{{cite journal |last1=Widmann |first1=Philipp |last2=Bucher |first2=Hugo |last3=Leu |first3=Marc |last4=Vennemann |first4=Torsten |last5=Bagherpour |first5=Borhan |last6=Schneebeli-Hermann |first6=Elke |last7=Goudemand |first7=Nicolas |last8=Schaltegger |first8=Urs |date=2020 |title=Dynamics of the Largest Carbon Isotope Excursion During the Early Triassic Biotic Recovery |journal=Frontiers in Earth Science |volume=8 |issue=196 |page=196 |doi=10.3389/feart.2020.00196 |bibcode=2020FrEaS...8..196W |doi-access=free}} was not recognised.{{cite book |last1=Hallam |first1=A. |url=https://archive.org/details/massextinctionst00hall_298 |title=Mass Extinctions and Their Aftermath |last2=Wignall |first2=P. B. |date=1997 |publisher=Oxford University Press, UK |isbn=978-0-19-158839-6 |page=[https://archive.org/details/massextinctionst00hall_298/page/n150 143] |quote=Extinctions with and at the close of the Triassic |url-access=limited}}

The Smithian–Spathian boundary extinction was linked to late eruptions of the Siberian Traps,{{Cite journal |last1=Du |first1=Yong |last2=Song |first2=Huyue |last3=Algeo |first3=Thomas J. |last4=Song |first4=Haijun |last5=Tian |first5=Li |last6=Chu |first6=Daoliang |last7=Shi |first7=Wei |last8=Li |first8=Chao |last9=Tong |first9=Jinnan |date=1 August 2022 |title=A massive magmatic degassing event drove the Late Smithian Thermal Maximum and Smithian–Spathian boundary mass extinction |journal=Global and Planetary Change |volume=215 |pages=103878 |doi=10.1016/j.gloplacha.2022.103878 |bibcode=2022GPC...21503878D }}{{cite journal |last1=Paton |first1=M. T. |last2=Ivanov |first2=A. V. |last3=Fiorentini |first3=M. L. |last4=McNaughton |first4=M. J. |last5=Mudrovska |first5=I. |last6=Reznitskii |first6=L. Z. |last7=Demonterova |first7=E. I. |date=1 September 2010 |title=Late Permian and Early Triassic magmatic pulses in the Angara–Taseeva syncline, Southern Siberian Traps and their possible influence on the environment |journal=Russian Geology and Geophysics |volume=51 |issue=9 |pages=1012–1020 |doi=10.1016/j.rgg.2010.08.009 |bibcode=2010RuGG...51.1012P }} which released warming greenhouse gases, resulting in global warming{{cite journal |last1=Romano |first1=Carlo |last2=Goudemand |first2=Nicolas |last3=Vennemann |first3=Torsten W. |last4=Ware |first4=David |last5=Schneebeli-Hermann |first5=Elke |last6=Hochuli |first6=Peter A. |last7=Brühwiler |first7=Thomas |last8=Brinkmann |first8=Winand |last9=Bucher |first9=Hugo |date=21 December 2012 |title=Climatic and biotic upheavals following the end-Permian mass extinction |journal=Nature Geoscience |volume=6 |issue=1 |pages=57–60 |doi=10.1038/ngeo1667 }} and in acidification, both on land{{cite journal |last1=Borruel-Abadía |first1=Violeta |last2=Barrenechea |first2=José F. |last3=Galán-Abellán |first3=Ana Belén |last4=De la Horra |first4=Raúl |last5=López-Gómez |first5=José |last6=Ronchi |first6=Ausonio |last7=Luque |first7=Francisco Javier |last8=Alonso-Azcárate |first8=Jacinto |last9=Marzo |first9=Mariano |date=20 June 2019 |title=Could acidity be the reason behind the Early Triassic biotic crisis on land? |journal=Chemical Geology |volume=515 |pages=77–86 |doi=10.1016/j.chemgeo.2019.03.035 |bibcode=2019ChGeo.515...77B }} and in the ocean.{{Cite journal |last1=Ye |first1=Feihong |last2=Zhao |first2=Laishi |last3=Zhang |first3=Lei |last4=Cui |first4=Ying |last5=Algeo |first5=Thomas J. |last6=Chen |first6=Zhong-Qiang |last7=Lyu |first7=Zhengyi |last8=Huang |first8=Yuangeng |last9=Bhat |first9=Ghulam M. |last10=Baud |first10=Aymon |date=August 2023 |title=Calcium isotopes reveal shelf acidification on southern Neotethyan margin during the Smithian-Spathian boundary cooling event |journal=Global and Planetary Change |language=en |volume=227 |pages=104138 |doi=10.1016/j.gloplacha.2023.104138 |bibcode=2023GPC...22704138Y }}{{cite journal |last1=Song |first1=Haijin |last2=Song |first2=Huyue |last3=Tong |first3=Jinnan |last4=Gordon |first4=Gwyneth W. |last5=Wignall |first5=Paul B. |last6=Tian |first6=Li |last7=Zheng |first7=Wang |last8=Algeo |first8=Thomas J. |last9=Liang |first9=Lei |last10=Bai |first10=Ruoyu |last11=Wu |first11=Kui |last12=Anbar |first12=Ariel D. |date=20 February 2021 |title=Conodont calcium isotopic evidence for multiple shelf acidification events during the Early Triassic |journal=Chemical Geology |volume=562 |page=120038 |doi=10.1016/j.chemgeo.2020.120038 |bibcode=2021ChGeo.56220038S }} A large spike in mercury concentrations relative to total organic carbon, much like during the Permian-Triassic extinction, has been suggested as another contributor to the extinction,{{cite journal |last1=Grasby |first1=Stephen E. |last2=Beauchamp |first2=Benoit |last3=Bond |first3=David P. G. |last4=Wignall |first4=Paul B. |last5=Sanei |first5=Hamed |year=2016 |title=Mercury anomalies associated with three extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) in NW Pangea |journal=Geological Magazine |volume=153 |issue=2 |pages=285–297 |doi=10.1017/S0016756815000436 |bibcode=2016GeoM..153..285G |doi-access=free }} although this is controversial and has been disputed by other research that suggests elevated mercury levels already existed by the middle Smithian.{{cite journal |last1=Hammer |first1=Øyvind |last2=Jones |first2=Morgan T. |last3=Schneebeli-Hermann |first3=Elke |last4=Hansen |first4=Bitten Bolvig |last5=Bucher |first5=Hugo |date=August 2019 |title=Are Early Triassic extinction events associated with mercury anomalies? A reassessment of the Smithian/Spathian boundary extinction |journal=Earth-Science Reviews |volume=195 |pages=179–190 |doi=10.1016/j.earscirev.2019.04.016 |bibcode=2019ESRv..195..179H |hdl=10852/76482 |url=https://www.zora.uzh.ch/id/eprint/170796/1/Hammer_et_al_2019_Hg_SSB-2.pdf |hdl-access=free }} Prior to the Smithian-Spathian Boundary extinction event, a flat gradient of latitudinal species richness is observed, suggesting that warmer temperatures extended into higher latitudes, allowing extension of geographic ranges of species adapted to warmer temperatures, and displacement or extinctions of species adapted to cooler temperatures.{{cite journal |last1=Brayard |first1=Arnaud |last2=Bucher |first2=Hugo |last3=Escarguel |first3=Gilles |last4=Fluteau |first4=Frédéric |last5=Bourquin |first5=Sylvie |last6=Galfetti |first6=Thomas |date=September 2006 |title=The Early Triassic ammonoid recovery: paleoclimatic significance of diversity gradients |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=239 |issue=3–4 |pages=374–395 |bibcode=2006PPP...239..374B |doi=10.1016/j.palaeo.2006.02.003}} Oxygen isotope studies on conodonts have revealed that temperatures rose in the first 2 million years of the Triassic, ultimately reaching sea surface temperatures of up to {{convert|40|°C|°F}} in the tropics during the Smithian.{{cite news |last1=Marshall |first1=Michael |date=18 October 2012 |title=Roasting Triassic heat exterminated tropical life |work=New Scientist |url=https://www.newscientist.com/article/dn22395-roasting-triassic-heat-exterminated-tropical-life/}} The extinction itself occurred during a subsequent drop in global temperatures (ca. 8°C over a geologically short period) in the latest Smithian; however, temperature alone cannot account for the Smithian-Spathian boundary extinction, because several factors were at play. An alternative explanation for the extinction event hypothesises the biotic crisis took place not at the Smithian-Spathian boundary but shortly before, during the Late Smithian Thermal Maximum (LSTM), with the Smithian-Spathian boundary itself being associated with cessation of intrusive magmatic activity of the Siberian Traps, along with significant global cooling,{{cite journal |last1=Song |first1=Huyue |last2=Du |first2=Yong |last3=Algeo |first3=Thomas J. |last4=Tong |first4=Jinnan |last5=Owens |first5=Jeremy D. |last6=Song |first6=Haijun |last7=Tian |first7=Li |last8=Qiu |first8=Haiou |last9=Zhu |first9=Yuanyuan |last10=Lyons |first10=Timothy W. |date=August 2019 |title=Cooling-driven oceanic anoxia across the Smithian/Spathian boundary (mid-Early Triassic) |journal=Earth-Science Reviews |volume=195 |pages=133–146 |doi=10.1016/j.earscirev.2019.01.009 |bibcode=2019ESRv..195..133S |doi-access=free }}{{cite journal |last1=Zhao |first1=He |last2=Dahl |first2=Tais W. |last3=Chen |first3=Zhong-Qiang |last4=Algeo |first4=Thomas J. |last5=Zhang |first5=Lei |last6=Liu |first6=Yongsheng |last7=Hu |first7=Zhaochu |last8=Hu |first8=Zihao |date=December 2000 |title=Anomalous marine calcium cycle linked to carbonate factory change after the Smithian Thermal Maximum (Early Triassic) |journal=Earth-Science Reviews |volume=211 |page=103418 |doi=10.1016/j.earscirev.2020.103418 }} after which a gradual biotic recovery took place over the early and middle Spathian,{{cite journal |last1=Zhang |first1=L. |last2=Zhao |first2=L. |last3=Chen |first3=Zhong-Qiang |last4=Algeo |first4=Thomas J. |last5=Li |first5=Y. |last6=Cao |first6=L. |date=12 March 2015 |title=Amelioration of marine environments at the Smithian–Spathian boundary, Early Triassic |journal=Biogeosciences |volume=12 |issue=5 |pages=1597–1613 |doi=10.5194/bg-12-1597-2015 |bibcode=2015BGeo...12.1597Z |doi-access=free }} along with a decline in continental weathering{{cite journal |last1=Song |first1=Haijun |last2=Wignall |first2=Paul B. |last3=Tong |first3=Jinnan |last4=Song |first4=Huyue |last5=Chen |first5=Jing |last6=Chu |first6=Daoliang |last7=Tian |first7=Li |last8=Luo |first8=Mao |last9=Zong |first9=Keqing |last10=Chen |first10=Yanlong |last11=Lai |first11=Xulong |last12=Zhang |first12=Kexin |last13=Wang |first13=Hongmei |date=15 August 2015 |title=Integrated Sr isotope variations and global environmental changes through the Late Permian to early Late Triassic |journal=Earth and Planetary Science Letters |volume=424 |pages=140–147 |doi=10.1016/j.epsl.2015.05.035 |bibcode=2015E&PSL.424..140S |url=https://eprints.whiterose.ac.uk/90240/9/Figs.pdf }} and a rejuvenation of ocean circulation.{{cite journal |last1=Song |first1=Huyue |last2=Tong |first2=Jinnan |last3=Algeo |first3=Thomas J. |last4=Koracek |first4=Micha |last5=Qiu |first5=Haiou |last6=Song |first6=Haijun |last7=Tian |first7=Li |last8=Chen |first8=Zhong-Qiang |date=June 2013 |title=Large vertical δ13CDIC gradients in Early Triassic seas of the South China craton: Implications for oceanographic changes related to Siberian Traps volcanism |journal=Global and Planetary Change |volume=105 |pages=7–20 |doi=10.1016/j.gloplacha.2012.10.023 |bibcode=2013GPC...105....7S }}

In the ocean, many large and mobile species moved away from the tropics, but large fish remained,{{cite journal |last1=Romano |first1=Carlo |last2=Jenks |first2=James F. |last3=Jattiot |first3=Romain |last4=Scheyer |first4=Torsten M. |last5=Bylund |first5=Kevin G. |last6=Bucher |first6=Hugo |date=19 July 2017 |title=Marine Early Triassic Actinopterygii from Elko County (Nevada, USA): implications for the Smithian equatorial vertebrate eclipse |journal=Journal of Paleontology |volume=91 |issue=5 |pages=1025–1046 |doi=10.1017/jpa.2017.36 |bibcode=2017JPal...91.1025R |doi-access=free}} and amongst the immobile species such as molluscs, only the ones that could cope with the heat survived; half the bivalves disappeared.{{cite book |last1=Hallam |first1=A. |url=https://archive.org/details/massextinctionst00hall_298 |title=Mass Extinctions and Their Aftermath |last2=Wignall |first2=P. B. |date=1997 |publisher=Oxford University Press, UK |isbn=978-0-19-158839-6 |page=[https://archive.org/details/massextinctionst00hall_298/page/n151 144] |url-access=limited}} Conodonts decreased in average size as a result of the extinction.{{cite journal |last1=Chen |first1=Yanlong |last2=Richoz |first2=Sylvain |last3=Krystyn |first3=Leopold |last4=Zhang |first4=Zhifei |date=August 2019 |title=Quantitative stratigraphic correlation of Tethyan conodonts across the Smithian-Spathian (Early Triassic) extinction event |journal=Earth-Science Reviews |volume=195 |pages=37–51 |doi=10.1016/j.earscirev.2019.03.004 |bibcode=2019ESRv..195...37C }} On land, the tropics were nearly devoid of life,{{cite journal |last1=Sun |first1=Y. |last2=Joachimski |first2=M. M. |last3=Wignall |first3=P. B. |last4=Yan |first4=C. |last5=Chen |first5=Y. |last6=Jiang |first6=H. |last7=Wang |first7=L. |last8=Lai |first8=X. |date=18 October 2012 |title=Lethally Hot Temperatures During the Early Triassic Greenhouse |journal=Science |volume=338 |issue=6105 |pages=366–370 |bibcode=2012Sci...338..366S |doi=10.1126/science.1224126 |pmid=23087244 }} with exceptionally arid conditions recorded in Iberia and other parts of Europe then at low latitude.{{cite journal |last1=Lloret |first1=Joan |last2=De la Hora |first2=Raúl |last3=Gretter |first3=Nicola |last4=Borruel-Abadía |first4=Violeta |last5=Barrenechea |first5=José F. |last6=Ronchi |first6=Ausonio |last7=Diez |first7=José B. |last8=Arche |first8=Alfredo |last9=López-Gómez |first9=José |date=September 2020 |title=Gradual changes in the Olenekian-Anisian continental record and biotic implications in the Central-Eastern Pyrenean basin, NE Spain |journal=Global and Planetary Change |volume=192 |page=103252 |doi=10.1016/j.gloplacha.2020.103252 |bibcode=2020GPC...19203252L }} Many big, active animals returned to the tropics, and plants recolonised on land, only when temperatures returned to normal.

There is evidence that life had recovered rapidly, at least locally. This is indicated by sites that show exceptionally high biodiversity (e.g. the earliest Spathian Paris Biota), which suggest that food webs were complex and comprised several trophic levels.

• Middle Buntsandstein (Germany)
• Jialingjiang Formation (South China)
• Nanlinghu Formation (Anhui, China)
• Sulphur Mountain Formation (British Columbia, Canada)
• Thaynes Group/Limestone (western USA)
• Virgin Formation (Utah, USA)
• Vikinghøgda Formation (Lusitaniadalen and Vendomdalen members) (Svalbard, Norway)

{{reflist}}

• {{cite journal |last1=Brack |first1=Peter |last2=Rieber |first2=Hans |last3=Nicora |first3=Alda |last4=Mundil |first4=Roland |title=The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale |journal=Episodes |date=1 December 2005 |volume=28 |issue=4 |pages=233–244 |doi=10.18814/epiiugs/2005/v28i4/001 |doi-access=free }}
• {{aut|Gradstein, F.M.; Ogg, J.G. & Smith, A.G.}}; 2004: A Geologic Time Scale 2004, Cambridge University Press.
• {{aut|Kiparisova, L.D. & Popov, J.N.}}; 1956: Расчленение нижнего отдела триасовой системы на ярусы (Subdivision of the lower series of the Triassic System into stages), Doklady Akademii Nauk SSSR 109(4), pp 842–845 {{in lang|ru}}.

• [http://www.stratigraphy.org/bak/geowhen/stages/Olenekian.html GeoWhen Database - Olenekian]
• [http://stratigraphy.science.purdue.edu/charts/Timeslices/8_Lower_Triassic.pdf Lower Triassic timescale] at the website of the subcommission for stratigraphic information of the ICS
• [https://web.archive.org/web/20060518101406/http://norges.uio.no/timescale/Fig16.1_Tri_colB.pdf Lower Triassic timescale] at the website of Norges Network of offshore records of geology and stratigraphy.

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{{Geological history|p|m}}

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Category:Geological ages

Category:Triassic geochronology

Category:Geology of Siberia

Category:Olenyok basin