Olson's Extinction

Olson's Extinction was a mass extinction that occurred 273 million years ago in the early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event.[1] It is named after Everett C. Olson. There was a hiatus and a sudden change in between the early Permian and middle/late Permian faunas. Since then this event has been realized across many groups, including plants, marine invertebrates, and tetrapods.

Identification

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'.[2][3] 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[4] or that multiple extinction pulses preceded the Permian–Triassic extinction event.[1][5][6] 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.[7]

Despite the closure of Olson's Gap, the presence of an extinction event at the Kungurian–Roadian 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.[8] 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.[9] 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.[9]

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.[10] Whether this climate change was a result of Earth's natural processes or exacerbated by another event is unknown.

Extinction patterns

On land

Plants

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.[11] 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%.[12] The extinction was particularly severe among free-sporing plants; seed plants seem to have been largely unaffected.[12]

Tetrapods

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) some of which were direct ancestors of mammals.[7] 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 appears to have taken place in two phases: Edaphosauridae and Ophiacodontidae died out across the Kungurian–Roadian boundary, while Caseidae and Therapsida diversified; later in the Roadian Sphenacodontidae died out and Caseidae went into decline.[13] Olson's extinction appears to have been the highest Paleozoic peak in extinction rate observed in Eureptilia, exceeding even the Permian–Triassic mass extinction.[14] Amphibians were also particularly hard-hit.[8]

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, the first evidence that one of these animals survived Olson's Extinction.[15] 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

Fish

Extinction rates in fish increased noticeably between the Cisuralian and the Guadalupian, the time of Olson's extinction.[16] However, origination rates also rose, and so there does not appear to have been any substantial decrease in species richness.[16] Using data on chondrichthyan diversity, Koot showed that there was little substantial decline in diversity until the middle of the Guadalupian.[17]

Recovery

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.[18]

References
  1. 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. PMC 2596898. PMID 18198148.CS1 maint: ref=harv (link)
  2. Lucas, S. G. (2004). "A global hiatus in the Middle Permian tetrapod fossil record" (PDF). Stratigraphy. 1: 47–64.CS1 maint: ref=harv (link)
  3. Ivakhnenko, M. F. (2005). "Comparative survey of Lower Permian tetrapod faunas of eastern Europe and South Africa". Paleontological Journal. 39 (1): 66–71.CS1 maint: ref=harv (link)
  4. Ward PD, Botha J, Buick R, De Kock MO, Erwin DH, Garrison GH, Kirschvink JL, Smith R (2005). "Abrupt and Gradual Extinction Among Late Permian Land Vertebrates in the Karoo Basin, South Africa". Science. 307 (5710): 709–714. Bibcode:2005Sci...307..709W. CiteSeerX 10.1.1.503.2065. doi:10.1126/science.1107068. PMID 15661973.
  5. 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. Bibcode:2006GSAB..118.1398R. doi:10.1130/B26011.1.
  6. Rampino MR, Prokoph A, Adler A (2000). "Tempo of the end-Permian event: High-resolution cyclostratigraphy at the Permian–Triassic boundary". Geology. 28 (7): 643–646. Bibcode:2000Geo....28..643R. doi:10.1130/0091-7613(2000)28<643:TOTEEH>2.0.CO;2. ISSN 0091-7613.
  7. Benton, M.J. (2012). "No gap in the Middle Permian record of terrestrial vertebrates". Geology. 40 (4): 339–342. Bibcode:2012Geo....40..339B. doi:10.1130/g32669.1.
  8. 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. Bibcode:2013Geo....41...43B. doi:10.1130/g33543.1.
  9. Brocklehurst, N.; Day, M.; Rubidge, B.; Frobisch, F. (2017). "Olson's Extinction and the Latitudinal Biodiversity Gradient". Proceedings of the Royal Society B. 284 (1852): 20170231. doi:10.1098/rspb.2017.0231. PMC 5394676. PMID 28381616.
  10. 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. Bibcode:2013Geo....41..587Z. doi:10.1130/G34078.1.
  11. 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.
  12. 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.
  13. 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.
  14. 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. Bibcode:2015NatSR...517104B. doi:10.1038/srep17104. PMC 4655484. PMID 26592209.
  15. 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. Bibcode:2011NW.....98.1027M. doi:10.1007/s00114-011-0856-2. PMID 22009069.CS1 maint: ref=harv (link)
  16. 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.
  17. Koot, M.B. 2013. Effects of the late Permian mass extinction on chondrichthyan palaeobiodiversity and distribution patterns
  18. Liu, J.; Rubidge, B; Li, J. (2009). "New basal synapsid supports Laurasian origin for therapsids" (PDF). Acta Palaeontologica Polonica. 54 (3): 393–400. doi:10.4202/app.2008.0071.CS1 maint: ref=harv (link)

Further reading
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