Earth:Olson's Extinction

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Short description: Mass extinction 273 million years ago

Olson's Extinction was a mass extinction that occurred 273 million years ago in the late Cisuralian or early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event.[1][2][3] It is named after Everett C. Olson. There was a sudden change between the early Permian and middle/late Permian faunas. Some authors also place a hiatus in the continental fossil record around that time,[4][2] but others disagree.[5][6][7][8][9] This event has been argued by some authors to have affected many taxa, including embryophytes, marine metazoans, and tetrapods.


The first evidence of extinction came when Everett C. Olson noted a hiatus between early Permian faunas dominated by pelycosaurs and therapsid-dominated faunas of the middle and late Permian. First considered to be a preservational gap in the fossil record, the event was originally dubbed 'Olson's Gap'.[4][10] To compound the difficulty in identifying the cause of the 'gap', researchers were having difficulty in resolving the uncertainty which exists regarding the duration of the overall extinction and about the timing and duration of various groups' extinctions within the greater process. Theories emerged which suggested the extinction was prolonged, spread out over several million years[11] or that multiple extinction pulses preceded the Permian–Triassic extinction event.[1][12][13] The impact of Olson's Extinction amplified the effects of the Permian–Triassic extinction event and the final extinction killed off only about 80% of species alive at that time while the other losses occurred during the first pulse or the interval between pulses.

During the 1990s and 2000s researchers gathered evidence on the biodiversity of plants, marine organisms and tetrapods that indicated an extinction pulse preceding the Permian–Triassic extinction event had a profound impact on life on land. On land Sahney and Benton showed that even discounting the sparse fossil assemblages from the extinction period, the event can be confirmed by the stages of time bracketing the event since well preserved sections of the fossil record from both before and after the event have been found and they referred to the event as 'Olson's Extinction'.[1] The 'Gap' was finally closed in 2012 when Michael Benton confirmed that the terrestrial fossil record of the Middle Permian is well represented by fossil localities in the American Southwest and European Russia and that the gap is not an artifact of a poor rock record since there is no correlation between geological and biological records of the Middle Permian.[6]

Despite the closure of Olson's Gap, the presence of an extinction event at the KungurianRoadian boundary was still disputed. It was argued that the observed decrease in diversity might be due to the shift in the location of greatest sample size from the palaeo-equatorial to the palaeo-temperate regions: equatorial regions tend to have a higher diversity in most modern groups.[14] However, a thorough review of the tetrapod-bearing formations during the Kungurian and the Roadian found evidence that the faunal turnover at this time is not a result of the shift in sampling locality; the early Permian temperate faunas are more similar to the early Permian equatorial faunas than the middle Permian temperate faunas.[7][15] It was also shown that throughout the Permian, the highest diversity was found in temperate regions rather than equatorial regions, and therefore the fall in diversity could not be due to increased sampling of temperate latitudes.[7]

Possible causes

There is no widely accepted theory for the cause of Olson's Extinction. Recent research has indicated that climate change may be a possible cause: extreme environments were observed from the Permian of Kansas which resulted from a combination of hot climate and acidic waters particularly coincident with Olson's Extinction.[16]

Extinction patterns

On land


Plants showed large turnover in the mid-to-late Permian and into the Triassic. The duration of higher extinction rates (>60%) in land plants was about 23.4 Myr, starting from Olson's Extinction and into the early Middle Triassic.[17] Olson's Extinction represents the third highest peak of extinction rates seen in plants throughout the Paleozoic, and the number of genera fell by 25%.[18] The extinction was particularly severe among free-sporing plants; seed plants seem to have been largely unaffected.[18]


The Permian was a time of rapid change for tetrapods; in particular there was a major changeover from faunas dominated by basal synapsids ("pelycosaurs”) and reptiliomorphs (Diadectes) to faunas dominated by therapsids (Dinocephalia, Anomodontia, Gorgonopsia, and Cynodontia) the lattermost subgroup of which were direct ancestors of mammals.[6] In 2008 Sahney and Benton[1] confirmed that this was not just a turnover (gradual replacement of one faunal complex by another) but a real extinction event in which a significant drop in the biodiversity of tetrapods on a global scale and community level occurred. The extinction may have taken place in two phases: Edaphosauridae and Ophiacodontidae died out around the Kungurian–Roadian boundary, while Caseidae and Therapsida diversified; later in the Roadian or slightly later Sphenacodontidae died out[3] and Caseidae went into decline.[19] Olson's extinction appears to have been the highest Paleozoic peak in extinction rate observed in Eureptilia, exceeding even the Permian–Triassic mass extinction.[20] Amphibians were also particularly hard-hit.[14]

In December 2011, the fossilized remains of the 'youngest' pelycosaur was described by Modesto et al. as from 260 million years ago in South Africa. This, and slightly older remains of varanopids, documents the fact that this clade, like some caseids,[21] survived Olson's Extinction.[22] This type of animal is called a disaster taxon, an organism that survives a major environmental disruption, perhaps forming the basis for a new adaptive radiation.

In the water


Extinction rates in fish increased noticeably between the Cisuralian and the Guadalupian, the time of Olson's extinction.[23] However, origination rates also rose, and so there does not appear to have been any substantial decrease in species richness.[23] Using data on chondrichthyan diversity, Koot showed that there was little substantial decline in diversity until the middle of the Guadalupian.[24]


Fauna did not recover fully from Olson's Extinction before the impact of the Permian-Triassic extinction event. Estimates of recovery time vary, where some authors indicated recovery was prolonged, lasting 30 million years into the Triassic.[1]

Several important events took place during Olson's Extinction, most notably the origin of therapsids, a group that includes the evolutionary ancestors of mammals. Further research on the recently identified primitive therapsid of the Xidagou Formation (Dashankou locality) in China of Roadian age may provide more information on this topic.[25]


  1. 1.0 1.1 1.2 1.3 1.4 Sahney, S.; Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time". Proceedings of the Royal Society B: Biological Sciences 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMID 18198148. 
  2. 2.0 2.1 Lucas, S. G. (1 July 2017). "Permian tetrapod extinction events" (in en). Earth-Science Reviews 170: 31–60. doi:10.1016/j.earscirev.2017.04.008. ISSN 0012-8252. 
  3. 3.0 3.1 Didier, Gilles; Laurin, Michel (9 December 2021). "Distributions of extinction times from fossil ages and tree topologies: the example of mid-Permian synapsid extinctions". PeerJ 9: e12577. doi:10.7717/peerj.12577. PMID 34966586. 
  4. 4.0 4.1 Lucas, S. G. (2004). "A global hiatus in the Middle Permian tetrapod fossil record". Stratigraphy 1: 47–64. 
  5. Reisz, Robert R.; Laurin, Michel (1 September 2001). <1229:TRMFVE>2.0.CO;2 "The reptile Macroleter: First vertebrate evidence for correlation of Upper Permian continental strata of North America and Russia". GSA Bulletin 113 (9): 1229–1233. doi:10.1130/0016-7606(2001)113<1229:TRMFVE>2.0.CO;2. ISSN 0016-7606.<1229:TRMFVE>2.0.CO;2. 
  6. 6.0 6.1 6.2 Benton, Michael James (2012). "No gap in the Middle Permian record of terrestrial vertebrates". Geology 40 (4): 339–342. doi:10.1130/g32669.1. Bibcode2012Geo....40..339B. Retrieved 21 March 2023. 
  7. 7.0 7.1 7.2 Brocklehurst, Neil; Day, Michael O.; Rubidge, Bruce S.; Frobisch, Jörg (5 April 2017). "Olson's Extinction and the Latitudinal Biodiversity Gradient". Proceedings of the Royal Society B 284 (1852): 20170231. doi:10.1098/rspb.2017.0231. PMID 28381616. PMC 5394676. Retrieved 21 March 2023. 
  8. Brocklehurst, Neil (10 June 2020). "Olson's Gap or Olson's Extinction? A Bayesian tip-dating approach to resolving stratigraphic uncertainty". Proceedings of the Royal Society B: Biological Sciences 287 (1928): 20200154. doi:10.1098/rspb.2020.0154. 
  9. Laurin, Michel; Hook, Robert W. (2022). "The age of North America’s youngest Paleozoic continental vertebrates: a review of data from the Middle Permian Pease River (Texas) and El Reno (Oklahoma) Groups". BSGF - Earth Sciences Bulletin 193: 10. doi:10.1051/bsgf/2022007. ISSN 1777-5817. 
  10. Ivakhnenko, M. F. (2005). "Comparative survey of Lower Permian tetrapod faunas of eastern Europe and South Africa". Paleontological Journal 39 (1): 66–71. 
  11. "Abrupt and Gradual Extinction Among Late Permian Land Vertebrates in the Karoo Basin, South Africa". Science 307 (5710): 709–714. 2005. doi:10.1126/science.1107068. PMID 15661973. Bibcode2005Sci...307..709W. Retrieved 21 March 2023. 
  12. Retallack, G.J.; Metzger, C.A.; Greaver, T.; Jahren, A.H.; Smith, R.M.H.; Sheldon, N.D. (2006). "Middle-Late Permian mass extinction on land". Bulletin of the Geological Society of America 118 (11–12): 1398–1411. doi:10.1130/B26011.1. Bibcode2006GSAB..118.1398R. Retrieved 21 March 2023. 
  13. Rampino, Michael R.; Prokoph, Andreas; Adler, Andre (2000). "Tempo of the end-Permian event: High-resolution cyclostratigraphy at the Permian–Triassic boundary". Geology 28 (7): 643–646. doi:10.1130/0091-7613(2000)28<643:TOTEEH>2.0.CO;2. ISSN 0091-7613. Bibcode2000Geo....28..643R. Retrieved 21 March 2023. 
  14. 14.0 14.1 Benson, R.; Upchurch, P. (2013). "Diversity trends in the establishment of terrestrial vertebrate ecosystems:Interactions between spatial and temporal sampling biases". Geology 41 (1): 43–46. doi:10.1130/g33543.1. Bibcode2013Geo....41...43B. Retrieved 21 March 2023. 
  15. Brocklehurst, Neil (15 May 2018). "An examination of the impact of Olson’s extinction on tetrapods from Texas". PeerJ 6. doi:10.7717/peerj.4767. Retrieved 21 March 2023. 
  16. Zambito J.J. IV.; Benison K.C (2013). "Extreme high temperatures and paleoclimate trends recorded in Permian ephemeral lake halite". Geology 41 (5): 587–590. doi:10.1130/G34078.1. Bibcode2013Geo....41..587Z. 
  17. Xiong, C.; Wang, Q. (2011). "Permian–Triassic land-plant diversity in South China: Was there a mass extinction at the Permian/Triassic boundary?". Paleobiology 37 (1): 157–167. doi:10.1666/09029.1. 
  18. 18.0 18.1 Cascales-Minana, B.; Diez, J.B.; Gerrienne, P.; Cleal, C.J. (2015). "A palaeobotanical perspective on the great end-Permian biotic crisis". Historical Biology 28 (8): 1066–1074. doi:10.1080/08912963.2015.1103237. 
  19. Brocklehurst, N.; Kammerer, C. F.; Fröbisch, J. (2013). "The early evolution of synapsids, and the influence of sampling on their fossil record". Paleobiology 39 (3): 470–490. doi:10.1666/12049. 
  20. Brocklehurst, N.; Ruta, M.; Muller; Fröbisch, J. (2015). "Elevated Extinction Rates as a Trigger for Diversification Rate Shifts: Early Amniotes as a Case Study". Scientific Reports 41: 43–46. doi:10.1038/srep17104. PMID 26592209. Bibcode2015NatSR...517104B. 
  21. Romano, Marco; Brocklehurst, Neil; Fröbisch, Jörg (21 October 2018). "The postcranial skeleton of Ennatosaurus tecton (Synapsida, Caseidae)". Journal of Systematic Palaeontology 16 (13): 1097–1122. doi:10.1080/14772019.2017.1367729. ISSN 1477-2019. 
  22. Sean P. Modesto; Roger M. H. Smith; Nicolás E. Campione; Robert R. Reisz (2011). "The last "pelycosaur": a varanopid synapsid from the Pristerognathus Assemblage Zone, Middle Permian of South Africa". Naturwissenschaften 98 (12): 1027–34. doi:10.1007/s00114-011-0856-2. PMID 22009069. Bibcode2011NW.....98.1027M. 
  23. 23.0 23.1 Friedman, M.; Sallan, L. (2012). "Five hundred million years of extinction and recovery: A phanerozoic survey of large-scale diversity patterns in fishes". Palaeontology 55 (4): 707–742. doi:10.1111/j.1475-4983.2012.01165.x. 
  24. Koot, M.B. 2013. Effects of the late Permian mass extinction on chondrichthyan palaeobiodiversity and distribution patterns
  25. Liu, J.; Rubidge, B; Li, J. (2009). "New basal synapsid supports Laurasian origin for therapsids". Acta Palaeontologica Polonica 54 (3): 393–400. doi:10.4202/app.2008.0071. 

Further reading