View source for Cretaceous–Paleogene extinction event

{{Short description|Mass extinction event about 66 million years ago}}
{{Redirect|Extinction of the non-avian dinosaurs|text=For other uses, see [[Extinction event]].}}
{{Featured article}}
{{use dmy dates|date=July 2023}}
{{Multiple image
| perrow            = 1/2/2
| total_width       = 300
| image1            = Impact event.jpg
| alt1              = Meteoroid entering the atmosphere with fireball
| image2            = Bali Khila Rajgad Maharashtra.jpg
| alt2              = dark rocky hill sourrounded by a small semi-desert plateau and deep cliffs
| image3            = KT boundary 054.jpg
| alt3              = rock hillside with rock striations
| image4            = K-T-boundary.JPG
| alt4              = rock in museum with layering
| image5            = Cretaceous Paleogene clay at Geulhemmergroeve.jpg
| alt5              = Cretaceous Paleogene clay layer with finger just below the boundary
| footer            = '''Clockwise from the top:'''
* Artist's rendering of an [[asteroid]] a few kilometers across colliding with the Earth. Such an impact can release the equivalent energy of several million nuclear weapons detonating simultaneously; 
* [[Badlands]] near [[Drumheller]], [[Alberta]], where erosion has exposed the [[K–Pg boundary]];
* Complex Cretaceous–Paleogene clay layer (gray) in the Geulhemmergroeve tunnels near [[Geulhem]], The Netherlands (finger is just below the actual Cretaceous–Paleogene boundary);
* [[Wyoming]] rock with an intermediate claystone layer that contains 1,000&nbsp;times more [[iridium]] than the upper and lower layers. Picture taken at the San Diego Natural History Museum;
* [[Rajgad Fort]]'s Citadel, an eroded hill from the [[Deccan Traps]], which are another hypothesized cause of the K{{ndash}}Pg extinction event.
}}
The '''Cretaceous–Paleogene''' ('''K–Pg''') '''extinction event''',{{efn|The abbreviation is derived from the juxtaposition of '''K''', the common abbreviation for the [[Cretaceous]], which in turn originates from the correspondent German term ''Kreide''; and '''Pg''', which is the abbreviation for the [[Paleogene]].}} also known as the '''K–T extinction''',{{efn|The former designation includes the term '[[Tertiary]]' (abbreviated as '''T'''), which is now discouraged as a formal geochronological unit by the [[International Commission on Stratigraphy]].<ref>{{cite book |author1=Ogg, James G. |author2= Gradstein, F. M. |author3=Gradstein, Felix M. |title=A geologic time scale 2004 |publisher=Cambridge University Press |location=Cambridge, UK |year=2004 |isbn=978-0-521-78142-8}}</ref>}} was the [[extinction event|mass extinction]] of three-quarters of the plant and animal [[species]] on Earth<ref>{{cite web |url= http://www.stratigraphy.org/index.php/ics-chart-timescale |title=International Chronostratigraphic Chart | website= stratigraphy.org |publisher=International Commission on Stratigraphy |year= 2015 |access-date=29 April 2015  |archive-url= https://web.archive.org/web/20140530005940/http://www.stratigraphy.org/index.php/ics-chart-timescale |archive-date=May 30, 2014}}</ref><ref name="Fortey">{{cite book |last=Fortey |first=Richard |author-link=Richard Fortey |title=Life: A natural history of the first four billion years of life on Earth |publisher=Vintage |year=1999 |pages=238–260 |isbn=978-0-375-70261-7 |title-link=Life: A Natural History of the First Four Billion Years of Life on Earth}}</ref> approximately 66&nbsp;million years ago. The event caused the extinction of all non-avian [[dinosaur]]s. Most other [[tetrapods]] weighing more than {{cvt|25|kg|lb}} also became extinct, with the exception of some [[ectothermic]] species such as [[sea turtles]] and [[crocodilians]].<ref name="PrimalF">{{cite book |title=Primal Forces |publisher=Graphic Arts Center Publishing |last1= Muench |first1=David | last2=Muench |first2=Marc |last3=Gilders |first3= Michelle A. |year=2000 |location=Portland, Oregon |page=20 |isbn=978-1-55868-522-2}}</ref> It marked the end of the Cretaceous period, and with it the [[Mesozoic]] era, while heralding the beginning of the current era, the [[Cenozoic]]. In the [[geologic record]], the K–Pg event is marked by a thin layer of [[sediment]] called the [[Cretaceous–Paleogene boundary|K–Pg boundary, Fatkito boundary or K–T boundary]], which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal [[iridium]],<ref name=":3">{{cite journal |last1=Jones |first1=Heather L. |last2=Westerhold |first2=Thomas |last3=Birch |first3=Heather |last4=Hull |first4=Pincelli |last5=Negra |first5=M. Hédi |last6=Röhl |first6=Ursula |last7=Sepúlveda |first7=Julio |last8=Vellekoop |first8=Johan |last9= Whiteside |first9=Jessica H. |last10=Alegret |first10=Laia |last11=Henehan |first11=Michael |last12=Robinson |first12=Libby |last13=Van Dijk |first13=Joep |last14=Bralower |first14=Timothy| display-authors= 3 |date=18 January 2023 |title=Stratigraphy of the Cretaceous/Paleogene (K/Pg) boundary at the Global Stratotype Section and Point (GSSP) in El Kef, Tunisia: New insights from the El Kef Coring Project |journal=[[Geological Society of America Bulletin]] |volume=135 |issue=9–10 |page=2451 |doi=10.1130/B36487.1 |bibcode=2023GSAB..135.2451J |s2cid=256021543|url=https://biblio.vub.ac.be/vubirfiles/105270956/Manuscript_text_revised.docx }}</ref><ref name=":4">{{cite journal |last1=Irizarry |first1= Kayla M. |last2=Witts |first2=James T. |last3=Garb |first3=Matthew P. |last4= Rashkova |first4=Anastasia |last5=Landman |first5=Neil H. |last6=Patzkowsky |first6=Mark E.| display-authors= 3 |date=15 January 2023 |title=Faunal and stratigraphic analysis of the basal Cretaceous-Paleogene (K-Pg) boundary event deposits, Brazos River, Texas, USA |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=610 |page=111334 |doi=10.1016/j.palaeo.2022.111334 |bibcode=2023PPP...61011334I |s2cid=254345541}}</ref><ref name=":5">{{cite journal |last1=Ferreira da Silva |first1=Luiza Carine |last2=Santos |first2=Alessandra |last3=Fauth |first3=Gerson |last4=Manríquez |first4=Leslie Marcela Elizabeth |last5=Kochhann |first5=Karlos Guilherme Diemer |last6=Do Monte Guerra |first6=Rodrigo |last7=Horodyski |first7=Rodrigo Scalise |last8=Villegas-Martín |first8=Jorge |last9=Ribeiro da Silva |first9=Rafael| display-authors= 3 |date=April 2023 |title=High-latitude Cretaceous–Paleogene transition: New paleoenvironmental and paleoclimatic insights from Seymour Island, Antarctica |journal= Marine Micropaleontology |volume=180 |page=102214 |doi= 10.1016/j.marmicro.2023.102214 |bibcode=2023MarMP.180j2214F |s2cid=256834649}}</ref> which is more common in [[asteroid]]s than in the [[Earth's crust]].<ref name="Schulte10" />

As originally proposed in 1980<ref name="The Asteroid and the Dinosaur (1981)">{{cite web |last1=Alvarez |first1=Luis |title=The Asteroid and the Dinosaur (Nova S08E08, 1981) |url=https://www.imdb.com/title/tt1435167/ |website=IMDB |date=10 March 1981 |publisher=PBS-WGBH/Nova |access-date=12 June 2020}}</ref> by a team of scientists led by [[Luis Walter Alvarez|Luis Alvarez]] and his son [[Walter Alvarez|Walter]], it is now generally thought that the K–Pg extinction was caused by the impact of a [[Chicxulub impactor|massive asteroid]] {{convert|10|to|15|km|mi|abbr=on|0}} wide,<ref name="AGU-20140409">{{cite press release |last1= Sleep |first1=Norman H. |last2=Lowe |first2=Donald R. |title=Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast |url= https://news.agu.org/press-release/scientists-reconstruct-ancient-impact-that-dwarfs-dinosaur-extinction-blast/ |date=9 April 2014| website= agu.org |publisher=[[American Geophysical Union]] |access-date=30 December 2016 |archive-url= https://web.archive.org/web/20170101045924/https://news.agu.org/press-release/scientists-reconstruct-ancient-impact-that-dwarfs-dinosaur-extinction-blast/ |archive-date=1 January 2017 |url-status=live}}</ref><ref>{{cite web |title=Dinosaur asteroid hit 'worst possible place' |last=Amos |first=Jonathan |date=15 May 2017 |url=https://www.bbc.com/news/science-environment-39922998 |access-date=16 March 2018 |website=[[BBC News Online]] |archive-url=https://web.archive.org/web/20180318162335/http://www.bbc.com/news/science-environment-39922998 |archive-date=18 March 2018 |url-status=live}}</ref> 66&nbsp;million years ago, which devastated the global environment, mainly through a lingering [[impact winter]] which halted [[photosynthesis]] in [[plant]]s and [[plankton]].<ref name="Alvarez" /><ref name=":11">{{cite journal |last1=Vellekoop |first1=J. |last2=Sluijs |first2=A. |last3=Smit |first3=J. |last4=Schouten |first4=S. |last5=Weijers |first5=J. W. H. |last6=Sinninghe Damste |first6=J. S. |last7=Brinkhuis |first7=H. |display-authors=3 |title=Rapid short-term cooling following the Chicxulub impact at the Cretaceous-Paleogene boundary |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=111 |issue=21 |pages=7537–7541 |date=May 2014 |pmid=24821785 |pmc=4040585 |doi=10.1073/pnas.1319253111 |bibcode=2014PNAS..111.7537V |doi-access=free}}</ref> The impact hypothesis, also known as the [[Alvarez hypothesis]], was bolstered by the discovery of the {{convert|180|km|mi|abbr=on|0}} [[Chicxulub crater]] in the [[Gulf of Mexico]]'s [[Yucatán Peninsula]] in the early 1990s,<ref name="Hildebrand, A. R. 1991">{{cite journal |last1=Hildebrand |first1=A. R. |last2=Penfield |first2=G. T. |last3=Kring |first3=David A. |last4=Pilkington |first4=Mark |last5=Camargo Z. |first5= Antonio |last6=Jacobsen |first6=Stein B. |last7=Boynton |first7=William V.| display-authors= 3 |year=1991 |title=Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatán peninsula, Mexico |journal=[[Geology (journal)|Geology]] |volume=19 |issue=9 |pages=867–871 |doi=10.1130/0091-7613(1991)019<0867:ccapct>2.3.co;2 |bibcode=1991Geo....19..867H}}</ref> which provided conclusive evidence that the K–Pg boundary clay represented debris from an [[asteroid impact]].<ref name="Schulte10">{{cite journal |last1=Schulte |first1=Peter |title=The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary |last31=Ravizza |first31=Greg |last32=Rebolledo-Vieyra |first32=Mario |last33=Reimold |first33=Wolf Uwe |last34=Robin |first34=Eric |last35=Salge |first35=Tobias |last36=Speijer |first36=Robert B. |last37=Sweet |first37=Arthur R. |last38=Urrutia-Fucugauchi |first38=Jaime |last39=Vajda |first39=Vivi |last40=Whalen |first40=Michael T. |last41=Willumsen |first41=Pi S. |first30=Elisabetta |last30=Pierazzo |first29=Richard D. |last29=Norris |first28=Douglas J. |last28=Nichols |first27=Clive R. |last27=Neal |first26=Joanna V. |last26=Morgan|author26-link= Joanna Morgan |first25=Alessandro |last25=Montanari |first24=Jay |last24=Melosh |first23=Takafumi |last23=Matsui |first22=Kenneth G. |last22=MacLeod |first21=David A. |last21=Kring |first20=Christian |last20=Koeberl |first19=Wolfgang |last19=Kiessling |first18=Kirk R. |last18=Johnson |first17=Sean P. S. |last17=Gulick |first16=Richard A. F. |last16=Grieve |first15=José M. |last15=Grajales-Nishimura |first14=Kazuhisa |last14=Goto |first13= Tamara J. |last13=Goldin |first12=Alexander |last12=Deutsch |journal=[[Science (journal)|Science]] |first11=Gareth S. |volume=327 |issue=5970 |last11= Collins |pages=1214–1218 |date=5 March 2010 |doi=10.1126/science.1177265 |first10=Charles S. |pmid=20203042 |bibcode=2010Sci...327.1214S |last2=Alegret |first2=L. |last3= Arenillas |first3=I. |last10=Cockell |last4=Arz |first4=José A. |last5=Barton |first5=Penny J. |last6=Bown |first6=Paul R. |last7=Bralower |first7= Timothy J. |last8=Christeson |first8= Gail L. |last9=Claeys |first9=Philippe |s2cid=2659741 |display-authors=3 |url= http://doc.rero.ch/record/210367/files/PAL_E4389.pdf }}</ref> The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid.<ref name="Schulte10" /> A 2016 drilling project into the Chicxulub [[peak ring]] confirmed that the peak ring comprised [[granite]] ejected within minutes from deep in the earth, but contained hardly any [[gypsum]], the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an [[aerosol]] into the atmosphere, causing longer-term effects on the climate and [[food chain]]. In October 2019, researchers asserted that the event rapidly [[Ocean acidification|acidified the oceans]] and produced long-lasting effects on the climate, detailing the mechanisms of the mass extinction.<ref name="NYT-20191021">{{cite news |last=Joel |first=Lucas |title=The dinosaur-killing asteroid acidified the ocean in a flash: the Chicxulub event was as damaging to life in the oceans as it was to creatures on land, a study shows. |url=https://www.nytimes.com/2019/10/21/science/chicxulub-asteroid-ocean-acid.html |date=21 October 2019 |work=[[The New York Times]] |access-date=24 October 2019 |archive-url= https://web.archive.org/web/20191024040435/https://www.nytimes.com/2019/10/21/science/chicxulub-asteroid-ocean-acid.html |archive-date=24 October 2019 |url-status=live}}</ref><ref name="PNAS-20191021">{{cite journal |last=Henehan |first= Michael J. |title=Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact |date=21 October 2019 |journal= Proceedings of the National Academy of Sciences of the United States of America |volume=116 |issue=45 |pages=22500–22504 |doi=10.1073/pnas.1905989116 |pmid= 31636204 |pmc=6842625|bibcode=2019PNAS..11622500H|doi-access=free }}</ref>

Other causal or contributing factors to the extinction may have been the [[Deccan Traps]] and other volcanic eruptions,<ref>{{cite book |editor-first=John|editor-last= Talent|title=Earth and Life: Global Biodiversity, Extinction Intervals and Biogeographic Perturbations Through Time |url= https://archive.org/details/earthlifeglobalb00tale |url-access=limited |year=2012 |isbn= 978-90-481-3427-4 |first=Gerta|last=Keller |author-link=Gerta Keller| chapter=The Cretaceous–Tertiary mass extinction, Chicxulub impact, and Deccan volcanism. Earth and life |pages=[https://archive.org/details/earthlifeglobalb00tale/page/n774 759]–793 |publisher=[[Springer (publisher)|Springer]]}}</ref><ref>{{cite magazine |first=Bianca |last=Bosker |title=The nastiest feud in science: A Princeton geologist has endured decades of ridicule for arguing that the fifth extinction was caused not by an asteroid but by a series of colossal volcanic eruptions. But she's reopened that debate |magazine=[[The Atlantic Monthly]] |date=September 2018 |url= https://www.theatlantic.com/magazine/archive/2018/09/dinosaur-extinction-debate/565769/ |access-date=2019-01-30 |archive-url= https://web.archive.org/web/20190221073809/https://www.theatlantic.com/magazine/archive/2018/09/dinosaur-extinction-debate/565769/ |archive-date=February 21, 2019 |url-status=live}}</ref> [[climate change (general concept)|climate change]], and sea level change. However, in January 2020, scientists reported that climate-modeling of the extinction event favored the asteroid impact and not [[volcanism]].<ref name= "NYT-20200116">{{cite news |last=Joel |first=Lucas |title=Asteroid or Volcano? New Clues to the Dinosaurs' Demise |url= https://www.nytimes.com/2020/01/16/science/dinosaurs-extinction-meteorite-volcano.html |date=16 January 2020 |work= The New York Times |access-date=17 January 2020}}</ref><ref name="SCI-2020017">{{cite journal |last1=Hull |first1=Pincelli M.|last2=Bornemann |first2=André |last3=Penman |first3=Donald E.|s2cid=210698721 |title=On impact and volcanism across the Cretaceous-Paleogene boundary |date=17 January 2020 |journal=[[Science (journal)|Science]] |volume=367 |issue=6475 |pages=266–272 |doi= 10.1126/science.aay5055 |doi-access=free |pmid=31949074 |bibcode=2020Sci...367..266H |hdl=20.500.11820/483a2e77-318f-476a-8fec-33a45fbdc90b| hdl-access=free}}</ref><ref name=":6">{{Cite journal |last1=Chiarenza |first1=Alfio Alessandro |last2=Farnsworth |first2= Alexander| last3= Mannion |first3=Philip D. |last4=Lunt |first4=Daniel J.|last5=Valdes |first5= Paul J.|last6=Morgan |first6=Joanna V. |last7=Allison |first7=Peter A. | display-authors= 3| date= 2020-07-21 |title=Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction |journal= Proceedings of the National Academy of Sciences of the United States of America |volume=117 |issue=29 |pages=17084–17093 |doi=10.1073/pnas.2006087117 |issn= 0027-8424 |pmid=32601204 |pmc=7382232 |bibcode=2020PNAS..11717084C |doi-access=free}}</ref>

A wide range of terrestrial species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs, along with many mammals, birds,<ref name= "longrichetal2011">{{cite journal |last1=Longrich |first1=Nicholas R. |last2=Tokaryk |first2=Tim |last3=Field |first3=Daniel J. |year=2011 |title=Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=108 |issue=37 |pages= 15253–15257 |bibcode=2011PNAS..10815253L |doi=10.1073/pnas.1110395108 |pmc= 3174646 |pmid=21914849 |doi-access=free}}</ref> lizards,<ref name="Longrich, N. R. 2012">{{cite journal |last1=Longrich |first1=N. R. |last2=Bhullar |first2=B.-A. S. |last3= Gauthier |first3=J. A. |title=Mass extinction of lizards and snakes at the Cretaceous-Paleogene boundary |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=52 |pages=21396–401 |date=December 2012 |pmid=23236177 |pmc=3535637 |doi=10.1073/pnas.1211526110 |doi-access=free |bibcode=2012PNAS..10921396L}}</ref> [[insect]]s,<ref>{{cite book |editor1=Hartman, J.H. |editor2=Johnson, K.R. |editor3=Nichols, D.J. |author1=Labandeira, C. C. |author2=Johnson, K. R. |author3=Lang, P. |date=2002 |chapter=Preliminary assessment of insect herbivory across the Cretaceous-Tertiary boundary: Major extinction and minimum rebound |title=The Hell Creek formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An integrated continental record of the end of the Cretaceous |pages=297–327 |publisher=Geological Society of America |isbn=978-0-8137-2361-7 |url=https://books.google.com/books?id=cHvcIeh2f84C}}</ref><ref name="Rehan2013">{{cite journal |last1=Rehan |first1=Sandra M. |last2=Leys |first2=Remko |last3=Schwarz |first3= Michael P. |title=First evidence for a massive extinction event affecting bees close to the K-T boundary |journal=[[PLOS ONE]] |volume=8 |issue=10 |year=2013 |pages= e76683 |doi=10.1371/journal.pone.0076683 |pmid=24194843 |pmc=3806776 |bibcode=2013PLoSO...876683R|doi-access=free }}</ref> plants, and all the [[pterosaur]]s.<ref name="Nichols, D. J 2008">{{cite book |author1=Nichols, D. J. |author2=Johnson, K. R. |year=2008 |title=Plants and the K–T Boundary |publisher=[[Cambridge University Press]] |location=Cambridge, UK}}</ref> In the oceans, the K–Pg extinction killed off [[Plesiosauria|plesiosaurs]] and [[mosasaur]]s and devastated [[teleost]] fish,<ref>{{cite journal | last=Friedman| first= M. |year=2009 |title= Ecomorphological selectivity among marine teleost fishes during the end-Cretaceous extinction |journal=[[Proceedings of the National Academy of Sciences]] |location= Washington, DC |volume=106 |issue=13 |pages=5218–5223 |pmid=19276106 |doi= 10.1073/pnas.0808468106 |pmc=2664034 |bibcode=2009PNAS..106.5218F|doi-access= free }}</ref> [[shark]]s, [[mollusk]]s (especially [[ammonites]], which became extinct), and many species of plankton. It is estimated that 75% or more of all species on Earth vanished.<ref name="Jablonski1994" /> However, the extinction also provided [[evolution]]ary opportunities: in its wake, many groups underwent remarkable [[adaptive radiation]]—sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the [[Paleogene]],<ref name="Alroy, J. 1999">{{cite journal |first=John|last=Alroy |author-link=John Alroy |year=1999 |title=The fossil record of North American Mammals: evidence for a Palaeocene evolutionary radiation |journal=[[Systematic Biology]] |volume=48 |issue=1 |pages=107–118 |pmid=12078635 |doi= 10.1080/106351599260472|doi-access=free}}</ref> evolving new forms such as [[equidae|horse]]s, [[cetacea|whale]]s, [[bat]]s, and [[primate]]s. The surviving group of dinosaurs were avians, a few species of ground and water fowl, which radiated into all modern species of birds.<ref name="Feduccia, A. 1995">{{cite journal |first=Alan |last=Feduccia |author-link=Alan Feduccia |year=1995 |title=Explosive evolution in Tertiary birds and mammals |journal=[[Science (journal)|Science]] |volume=267 |issue=5198 |pages=637–638 |s2cid=42829066 |pmid=17745839 |doi=10.1126/science.267.5198.637 |bibcode=1995Sci...267..637F}}</ref> Among other groups, teleost fish<ref name="Friedman, M. 2010">{{cite journal |author=Friedman, M. |year=2010 |title=Explosive morphological diversification of spiny-finned teleost fishes in the aftermath of the end-Cretaceous extinction |journal=[[Proceedings of the Royal Society B]] |volume=277 |issue=1688 |pages=1675–1683 |pmid=20133356 |doi= 10.1098/rspb.2009.2177 |pmc=2871855}}</ref> and perhaps lizards<ref name= "Longrich, N. R. 2012" /> also radiated.

==Extinction patterns==
{{annotated image/Extinction|float=left}} The K–Pg extinction event was severe, global, rapid, and selective, eliminating a vast number of species. Based on marine fossils, it is estimated that 75% or more of all species became extinct.<ref name="Jablonski1994">{{cite journal |author=Jablonski, D. |year=1994 |title=Extinctions in the fossil record (and discussion) |journal=Philosophical Transactions of the Royal Society of London B |volume=344 |issue=1307 |pages=11–17 |doi=10.1098/rstb.1994.0045 |last2=Chaloner |first2=W. G.}}</ref>

The event appears to have affected all continents at the same time. Non-avian [[dinosaur]]s, for example, are known from the [[Maastrichtian]] of North America, [[Europe]], Asia, [[Africa]], South America, and [[Antarctica]], but are unknown from the Cenozoic anywhere in the world.<ref>{{cite book |author1=Weishampel, D. B. |author2=Barrett, P. M. |year=2004 |contribution=Dinosaur distribution |title=The Dinosauria |publisher=University of California Press |isbn=978-0-520-24209-8 |editor1=Weishampel, David B. |location=Berkeley, CA |pages=[https://archive.org/details/dinosauriandedit00weis/page/n535 517]–606 |url=https://archive.org/details/dinosauriandedit00weis |oclc=441742117 |edition=2nd |editor2=Dodson, Peter |editor3=Osmólska, Halszka |url-access=limited}}</ref> Similarly, fossil pollen shows devastation of the plant communities in areas as far apart as [[New Mexico]], [[Alaska]], [[China]], and [[New Zealand]].<ref name="Nichols, D. J 2008" /> Nevertheless, high latitudes appear to have been less strongly affected than low latitudes.<ref>{{Cite journal |last1=Barrera |first1=Enriqueta |last2=Keller |first2=Gerta |date=1 October 1994 |title=Productivity across the Cretaceous/Tertiary boundary in high latitudes |journal=[[Geological Society of America Bulletin]] |volume=106 |issue=10 |pages=1254–1266 |doi=10.1130/0016-7606(1994)106<1254:PATCTB>2.3.CO;2}}</ref>

Despite the event's severity, there was significant variability in the rate of extinction between and within different [[clade]]s. Species that depended on [[photosynthesis]] declined or became extinct as atmospheric particles blocked sunlight and reduced the [[solar energy]] reaching the ground. This plant extinction caused a major reshuffling of the dominant plant groups.<ref name="autogenerated347">{{cite journal |author1=Wilf, P. |author2=Johnson, K.R. |year=2004 |title=Land plant extinction at the end of the Cretaceous: A quantitative analysis of the North Dakota megafloral record |journal=[[Paleobiology (journal)|Paleobiology]] |volume=30 |issue=3 |pages=347–368 |doi=10.1666/0094-8373(2004)030<0347:LPEATE>2.0.CO;2 |s2cid=33880578 }}</ref> [[Omnivores]], [[insectivores]], and [[carrion]]-eaters survived the extinction event, perhaps because of the increased availability of their food sources. Neither strictly [[herbivorous]] nor strictly [[carnivorous]] [[mammal]]s seem to have survived. Rather, the surviving mammals and birds fed on [[insect]]s, [[worm]]s, and [[snail]]s, which in turn fed on [[detritus (biology)|detritus]] (dead plant and animal matter).<ref name="MacLeod">{{cite journal |year=1997 |title=The Cretaceous–Tertiary biotic transition |journal=[[Journal of the Geological Society]] |volume=154 |issue=2 |pages=265–292 |doi=10.1144/gsjgs.154.2.0265 |author1=MacLeod, N. |author2=Rawson, P.F. |author3=Forey, P.L. |author4=Banner, F.T. |author5=Boudagher-Fadel, M.K. |author6=Bown, P.R. |author7=Burnett, J.A. |author8=Chambers, P. |author9=Culver, S. |author10=Evans, S.E. |author11=Jeffery, C. |author12=Kaminski, M.A. |author13=Lord, A.R. |author14=Milner, A.C. |author15=Milner, A.R. |author16=Morris, N. |author17=Owen, E. |author18=Rosen, B.R. |author19=Smith, A.B. |author20=Taylor, P.D. |author21=Urquhart, E. |author22=Young, J.R. |s2cid=129654916 |bibcode=1997JGSoc.154..265M }}</ref><ref name="SheehanHansen">{{cite journal |last1=Sheehan |first1=Peter M. |last2=Hansen |first2=Thor A. |year=1986 |title=Detritus feeding as a buffer to extinction at the end of the Cretaceous |journal=[[Geology (journal)|Geology]] |volume=14 |issue=10 |pages=868–870 |doi=10.1130/0091-7613(1986)14<868:DFAABT>2.0.CO;2 |bibcode=1986Geo....14..868S |s2cid=54860261 |url=http://pdfs.semanticscholar.org/83c8/1affaceb4d7da17e5f8ec0fd91c033adb08f.pdf |archive-url=https://web.archive.org/web/20190227164831/http://pdfs.semanticscholar.org/83c8/1affaceb4d7da17e5f8ec0fd91c033adb08f.pdf  |archive-date=2019-02-27 }}</ref><ref>{{cite journal |title=Faunal evidence for reduced productivity and uncoordinated recovery in Southern Hemisphere Cretaceous-Paleogene boundary sections |author1=Aberhan, M. |author2=Weidemeyer, S. |author3=Kieesling, W. |author4=Scasso, R.A. |author5=Medina, F.A. |year=2007 |journal=[[Geology (journal)|Geology]] |volume=35 |issue=3 |pages=227–230 |doi=10.1130/G23197A.1 |bibcode=2007Geo....35..227A}}</ref>

In [[stream]] [[Biocoenosis|communities]] and [[lake ecosystem]]s, few animal groups became extinct, including large forms like [[crocodyliform]]s and [[Choristodera|champsosaurs]], because such communities rely less directly on food from living plants, and more on detritus washed in from the land, protecting them from extinction.<ref name =major>{{cite journal |title=Major extinctions of land-dwelling vertebrates at the Cretaceous-Tertiary boundary, eastern Montana |author1=Sheehan, Peter M. |author2=Fastovsky, D. E. |year=1992 |journal=[[Geology (journal)|Geology]] |volume=20 |issue=6 |pages= 556–560 |doi=10.1130/0091-7613(1992)020<0556:MEOLDV>2.3.CO;2 |bibcode=1992Geo....20..556S }}</ref><ref>{{Cite journal |last1=García-Girón |first1=Jorge |last2=Chiarenza |first2=Alfio Alessandro |last3=Alahuhta |first3=Janne |last4=DeMar |first4=David G. |last5=Heino |first5=Jani |last6=Mannion |first6=Philip D. |last7=Williamson |first7=Thomas E. |last8=Wilson Mantilla |first8=Gregory P. |last9=Brusatte |first9=Stephen L. |date=2022-12-09 |title=Shifts in food webs and niche stability shaped survivorship and extinction at the end-Cretaceous |journal=Science Advances |volume=8 |issue=49 |pages=eadd5040 |doi=10.1126/sciadv.add5040 |pmc=9728968 |pmid=36475805}}</ref> Modern crocodilians can live as scavengers and survive for months without food, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous. Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the [[Pelagic zone|water column]] than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on [[primary production]] from living [[phytoplankton]], while animals on the [[ocean floor]] always or sometimes feed on detritus.<ref name="MacLeod" /> [[Coccolithophorids]] and [[mollusk]]s (including [[ammonite]]s, [[rudist]]s, [[freshwater snail]]s, and [[mussel]]s), and those organisms whose [[food chain]] included these shell builders, became extinct or suffered heavy losses. For example, it is thought that [[Ammonoidea|ammonites]] were the principal food of [[mosasaur]]s, a group of giant marine [[reptiles]] that became extinct at the boundary.<ref name="Kauffman">{{cite journal |author=Kauffman, E. |title=Mosasaur predation on upper Cretaceous nautiloids and ammonites from the United States Pacific Coast |journal=[[PALAIOS]] |volume=19 |issue=1 |pages=96–100 |doi=10.1669/0883-1351(2004)019<0096:MPOUCN>2.0.CO;2 |year=2004 |bibcode=2004Palai..19...96K |s2cid=130690035 |url=http://doc.rero.ch/record/14992/files/PAL_E2143.pdf }}</ref>

The K–Pg extinction had a profound effect on the [[Timeline of the evolutionary history of life|evolution of life on Earth]]. The elimination of dominant Cretaceous groups allowed other organisms to take their place, causing a remarkable amount of [[adaptive radiation|species diversification]] during the Paleogene Period.<ref name="Alroy, J. 1999" /> After the K–Pg extinction event, biodiversity required substantial time to recover, despite the existence of abundant vacant [[ecological niche]]s.<ref name="MacLeod" /> Evidence from the [[Salamanca Formation]] suggests that biotic recovery was more rapid in the Southern Hemisphere than in the Northern Hemisphere.<ref>{{cite journal |last1=Clyde |first1=William C. |last2=Wilf |first2=Peter |last3=Iglesias |first3=Ari |last4=Slingerland |first4=Rudy L. |last5=Barnum |first5=Timothy |last6=Bijl |first6=Peter K. |last7=Bralower |first7=Timothy J. |last8=Brinkhuis |first8=Henk |last9=Comer |first9=Emily E. |last10=Huber |first10=Brian T. |last11=Ibañez-Mejia |first11=Mauricio |last12=Jicha |first12=Brian R. |last13=Krause |first13=J. Marcelo |last14=Schueth |first14=Jonathan D. |last15=Singer |first15=Bradley S. |date=1 March 2014 |title=New age constraints for the Salamanca Formation and lower Río Chico Group in the western San Jorge Basin, Patagonia, Argentina: Implications for Cretaceous-Paleogene extinction recovery and land mammal age correlations |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article/126/3-4/289/125989/New-age-constraints-for-the-Salamanca-Formation |journal=[[Geological Society of America Bulletin]] |volume=126 |issue=3–4 |pages=289–306 |bibcode=2014GSAB..126..289C |doi=10.1130/B30915.1 |s2cid=129962470 |access-date=21 December 2022 |last16=Raigemborn |first16=María Sol |last17=Schmitz |first17=Mark D. |last18=Sluijs |first18=Appy |last19=Zamaloa |first19=María del Carmen|hdl=11336/80135 |hdl-access=free }}</ref>

===Microbiota===
The [[K–Pg boundary]] represents one of the most dramatic turnovers in the [[fossil record]] for various [[calcareous]] [[nanoplankton]] that formed the [[calcium]] deposits for which the Cretaceous is named. The turnover in this group is clearly marked at the species level.<ref>{{cite journal |author=Pospichal, J. J. |title=Calcareous nannofossils and clastic sediments at the Cretaceous–Tertiary boundary, northeastern Mexico |year=1996 |journal=[[Geology (journal)|Geology]] |volume=24 |issue=3 |pages=255–258 |doi=10.1130/0091-7613(1996)024<0255:CNACSA>2.3.CO;2 |bibcode=1996Geo....24..255P }}</ref><ref>{{cite journal |author=Bown, P. |year=2005 |title=Selective calcareous nannoplankton survivorship at the Cretaceous–Tertiary boundary |journal=[[Geology (journal)|Geology]] |volume=33 |issue=8 |pages=653–656 |doi=10.1130/G21566.1 |bibcode=2005Geo....33..653B }}</ref> Statistical analysis of [[marine (ocean)|marine]] losses at this time suggests that the decrease in diversity was caused more by a sharp increase in extinctions than by a decrease in [[speciation]].<ref>{{cite journal |author1=Bambach, R. K. |author2=Knoll, A. H. |author3=Wang, S. C. |year=2004 |title=Origination, extinction, and mass depletions of marine diversity |journal=[[Paleobiology (journal)|Paleobiology]] |volume=30 |issue=4 |pages=522–542 |doi= 10.1666/0094-8373(2004)030<0522:OEAMDO>2.0.CO;2 |s2cid=17279135 |url=http://biology.kenyon.edu/courses/biol241/extinction%20and%20marine%20diversity%20banbach%202004.pdf }}</ref> Major spatial differences existed in calcareous nannoplankton diversity patterns; in the Southern Hemisphere, the extinction was less severe and recovery occurred much faster than in the Northern Hemisphere.<ref>{{Cite journal |last1=Jiang |first1=Shijun |last2=Bralower |first2=Timothy J. |last3=Patzkowsky |first3=Mark E. |last4=Kump |first4=Lee R. |last5=Schueth |first5=Jonathan D. |date=28 February 2010 |title=Geographic controls on nannoplankton extinction across the Cretaceous/Palaeogene boundary |url=https://www.nature.com/articles/ngeo775 |journal=[[Nature Geoscience]] |language=en |volume=3 |issue=4 |pages=280–285 |doi=10.1038/ngeo775 |issn=1752-0908 |access-date=22 August 2024}}</ref> Following the extinction, survivor communities dominated for several hundred thousand years. The North Pacific acted as a diversity hotspot from which later nannoplankton communities radiated as they replaced survivor faunas across the globe.<ref>{{Cite journal |last1=Schueth |first1=Jonathan D. |last2=Bralower |first2=Timothy J. |last3=Jiang |first3=Shijun |last4=Patzkowsky |first4=Mark E. |date=September 2015 |title=The role of regional survivor incumbency in the evolutionary recovery of calcareous nannoplankton from the Cretaceous/Paleogene (K/Pg) mass extinction |journal=[[Paleobiology (journal)|Paleobiology]] |language=en |volume=41 |issue=4 |pages=661–679 |doi=10.1017/pab.2015.28 |issn=0094-8373}}</ref>

The K–Pg boundary record of [[dinoflagellate]]s is not so well understood, mainly because only [[microbial cyst]]s provide a fossil record, and not all dinoflagellate species have cyst-forming stages, which likely causes diversity to be underestimated.<ref name="MacLeod" /> Recent studies indicate that there were no major shifts in dinoflagellates through the boundary layer.<ref>{{cite journal |author=Gedl, P. |s2cid=128771186 |title=Dinoflagellate cyst record of the deep-sea Cretaceous-Tertiary boundary at Uzgru, Carpathian Mountains, Czech Republic |journal=Special Publications of the Geological Society of London |year=2004 |volume=230 |issue=1 |pages=257–273 |doi=10.1144/GSL.SP.2004.230.01.13 |bibcode=2004GSLSP.230..257G}}</ref> There were blooms of the taxa ''Thoracosphaera operculata'' and ''Braarudosphaera bigelowii'' at the boundary.<ref>{{cite book |last1=Tantawy |first1=Abdel Aziz |editor-last1=Keller |editor-first1=Gerta |editor-last2=Adatte |editor-first2=Thierry |date=2011 |title=The End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas |chapter=Calcareous Nannofossils Across the Cretaceous–Tertiary Boundary at Brazos, Texas, U.S.A.: Extinction and Survivorship, Biostratigraphy, and Paleoecology |url=https://pubs.geoscienceworld.org/sepm/books/edited-volume/1197/The-End-Cretaceous-Mass-Extinction-and-the |chapter-url=https://pubs.geoscienceworld.org/sepm/books/edited-volume/1197/chapter-abstract/10721260/Calcareous-Nannofossils-Across-the-Cretaceous?redirectedFrom=fulltext |publisher=Society of Sedimentary Geology |pages=157–178 |doi=10.2110/sepmsp.100.157 |isbn=9781565763098}}</ref>

[[Radiolaria]] have left a geological record since at least the [[Ordovician]] times, and their mineral fossil skeletons can be tracked across the K–Pg boundary. There is no evidence of mass extinction of these organisms, and there is support for high productivity of these species in [[Antarctic Circle|southern high latitudes]] as a result of cooling temperatures in the early [[Paleocene]].<ref name="MacLeod" /> Approximately 46% of [[diatom]] species survived the transition from the [[Cretaceous]] to the Upper Paleocene, a significant turnover in species but not a catastrophic extinction.<ref name="MacLeod" /><ref>{{cite journal |author=MacLeod, N. |s2cid=129875020 |title=Impacts and marine invertebrate extinctions |year=1998 |journal=Special Publications of the Geological Society of London |volume=140 |pages=217–246 |doi=10.1144/GSL.SP.1998.140.01.16 |issue=1 |bibcode=1998GSLSP.140..217M }}</ref>

The occurrence of [[plankton]]ic [[foraminifera]] across the K–Pg boundary has been studied since the 1930s.<ref>{{cite book |last=Courtillot |first=V. |title=Evolutionary Catastrophes: The science of mass extinction |publisher=Cambridge University Press |year=1999 |location=Cambridge, UK |page=2 |url=https://books.google.com/books?id=qiegJbafYkUC&pg=PA23 |isbn=978-0-521-58392-3}}</ref> Research spurred by the possibility of an impact event at the K–Pg boundary resulted in numerous publications detailing planktonic foraminiferal extinction at the boundary;<ref name="MacLeod" /> there is ongoing debate between groups which think the evidence indicates substantial extinction of these species at the K–Pg boundary,<ref>{{Cite journal |last1=Hansen |first1=T. |last2=Farrand |first2=R.B. |last3=Montgomery |first3=H.A. |last4=Billman |first4=H.G. |last5=Blechschmidt |first5=G. |date=September 1987 |title=Sedimentology and extinction patterns across the Cretaceous-Tertiary boundary interval in east Texas |journal=[[Cretaceous Research]] |language=en |volume=8 |issue=3 |pages=229–252 |doi=10.1016/0195-6671(87)90023-1}}</ref><ref>{{cite journal |author1=Arenillas, I. |author2=Arz, J. A. |author3=Molina, E. |author4=Dupuis, C. |title=An independent test of planktic foraminiferal turnover across the Cretaceous/Paleogene (K/P) boundary at El&nbsp;Kef, Tunisia: Catastrophic mass extinction and possible survivorship |journal=Micropaleontology |year=2000 |volume=46 |issue=1 |pages=31–49 |jstor=1486024}}</ref> and those who think the evidence supports a gradual extinction through the boundary.<ref>{{Cite journal |last=Keller |first=Gerta |date=April 1993 |title=The Cretaceous-Tertiary boundary transition in the Antarctic Ocean and its global implications |journal=Marine Micropaleontology |language=en |volume=21 |issue=1–3 |pages=1–45 |doi=10.1016/0377-8398(93)90010-U}}</ref><ref>{{Cite journal |last1=Macleod |first1=Norman |last2=Keller |first2=Gerta |date=1 November 1991 |title=How complete are Cretaceous /Tertiary boundary sections? A chronostratigraphic estimate based on graphic correlation |journal=[[Geological Society of America Bulletin]] |language=en |volume=103 |issue=11 |pages=1439 |doi=10.1130/0016-7606(1991)103<1439:HCACTB>2.3.CO;2 |issn=0016-7606}}</ref><ref name="MacLeod2">{{cite book |last=MacLeod |first=N. |year=1996 |article=Nature of the Cretaceous-Tertiary (K–T) planktonic foraminiferal record: Stratigraphic confidence intervals, Signor–Lipps effect, and patterns of survivorship |title=Cretaceous–Tertiary Mass Extinctions: Biotic and environmental changes |editor1=MacLeod, N. |editor2=Keller, G. |publisher=W.W. Norton |pages=85–138 |isbn=978-0-393-96657-2}}</ref> There is strong evidence that local conditions heavily influenced diversity changes in planktonic foraminifera.<ref>{{Cite journal |last1=Keller |first1=G. |last2=Li |first2=L. |last3=MacLeod |first3=N. |date=1 January 1996 |title=The Cretaceous/Tertiary boundary stratotype section at El Kef, Tunisia: how catastrophic was the mass extinction? |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=119 |issue=3 |pages=221–254 |doi=10.1016/0031-0182(95)00009-7 |issn=0031-0182}}</ref> Low and mid-latitude communities of planktonic foraminifera experienced high extinction rates, while high latitude faunas were relatively unaffected.<ref>{{Cite journal |last1=MacLeod |first1=Norman |last2=Keller |first2=Gerta |date=Spring 1994 |title=Comparative biogeographic analysis of planktic foraminiferal survivorship across the Cretaceous/Tertiary (K/T) boundary |journal=[[Paleobiology (journal)|Paleobiology]] |language=en |volume=20 |issue=2 |pages=143–177 |doi=10.1017/S0094837300012653 |issn=0094-8373}}</ref>

Numerous species of [[benthic]] foraminifera became extinct during the event, presumably because they depend on organic debris for nutrients, while [[biomass (ecology)|biomass]] in the ocean is thought to have decreased. As the marine microbiota recovered, it is thought that increased speciation of benthic foraminifera resulted from the increase in food sources.<ref name=MacLeod/> In some areas, such as Texas, benthic foraminifera show no sign of any major extinction event, however.<ref>{{Cite journal |last1=Schulte |first1=Peter |last2=Speijer |first2=Robert |last3=Mai |first3=Hartmut |last4=Kontny |first4=Agnes |date=1 February 2006 |title=The Cretaceous–Paleogene (K–P) boundary at Brazos, Texas: Sequence stratigraphy, depositional events and the Chicxulub impact |journal=[[Sedimentary Geology (journal)|Sedimentary Geology]] |language=en |volume=184 |issue=1–2 |pages=77–109 |doi=10.1016/j.sedgeo.2005.09.021|url=https://lirias.kuleuven.be/handle/123456789/77377 }}</ref> Phytoplankton recovery in the early Paleocene provided the food source to support large benthic foraminiferal assemblages, which are mainly detritus-feeding. Ultimate recovery of the benthic populations occurred over several stages lasting several hundred thousand years into the early Paleocene.<ref>{{cite journal |title=Deep-sea benthic foraminiferal recolonisation following a volcaniclastic event in the lower Campanian of the Scaglia Rossa Formation (Umbria-Marche Basin, central Italy) |author1=Galeotti, S. |author2=Bellagamba, M. |author3=Kaminski, M. A. |author4=Montanari, A. |year=2002 |journal=Marine Micropaleontology |volume=44 |issue=1–2 |pages=57–76 |doi=10.1016/s0377-8398(01)00037-8 |bibcode=2002MarMP..44...57G}}</ref><ref>{{cite journal |title=8. Cretaceous to Paleogene benthic foraminifers from the Iberia abyssal plain |author1=Kuhnt, W. |author2=Collins, E. S. |year=1996 |journal=Proceedings of the Ocean Drilling Program, Scientific Results |volume=149 |pages=203–216 |doi=10.2973/odp.proc.sr.149.254.1996 |series=Proceedings of the Ocean Drilling Program }}</ref>

=== Marine invertebrates ===
[[File:DiscoscaphitesirisCretaceous.jpg|thumb|alt=spiral shell with embedded rock two centimeters across|''Discoscaphites iris'' [[ammonite]] from the [[Owl Creek Formation]] (Upper Cretaceous), Owl Creek, Ripley, Mississippi]]
There is significant variation in the fossil record as to the extinction rate of [[marine invertebrates]] across the K–Pg boundary. The apparent rate is influenced by a lack of fossil records, rather than extinctions.<ref name="MacLeod" />

[[Ostracod]]s, a class of small [[crustacean]]s that were prevalent in the upper Maastrichtian, left fossil deposits in a variety of locations. A review of these fossils shows that ostracod diversity was lower in the Paleocene than any other time in the [[Cenozoic]]. Current research cannot ascertain whether the extinctions occurred prior to, or during, the boundary interval.<ref>{{cite book |author1=Coles, G. P. |author2=Ayress, M. A. |author3=Whatley, R. C. |year=1990 |contribution=A comparison of North Atlantic and 20 Pacific deep-sea Ostracoda |title=Ostracoda and Global Events |pages=287–305 |editor1=Whatley, R. C. |editor2=Maybury, C. |publisher=Chapman & Hall |isbn=978-0-442-31167-4}}</ref><ref>{{cite journal |title=Late Maastrichtian and Danian Ostracode Faunas from Northern Alaska: Reconstructions of Environment and Paleogeography |author1=Brouwers, E. M. |author2=de Deckker, P. |year=1993 |journal=[[PALAIOS]] |volume=8 |issue=2 |pages=140–154 |doi=10.2307/3515168 |jstor=3515168 |bibcode=1993Palai...8..140B}}</ref> Ostracods that were heavily sexually selected were more vulnerable to extinction,<ref>{{Cite journal |last1=Martins |first1=Maria João Fernandes |last2=Hunt |first2=Gene |last3=Thompson |first3=Carmi Milagros |last4=Lockwood |first4=Rowan |last5=Swaddle |first5=John P. |last6=Puckett |first6=T. Markham |date=26 August 2020 |title=Shifts in sexual dimorphism across a mass extinction in ostracods: implications for sexual selection as a factor in extinction risk |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=287 |issue=1933 |doi=10.1098/rspb.2020.0730 |issn=0962-8452 |pmc=7482269 |pmid=32811315 }}</ref> and ostracod sexual dimorphism was significantly rarer following the mass extinction.<ref>{{Cite journal |last1=Samuels-Fair |first1=Maya |last2=Martins |first2=Maria João Fernandes |last3=Lockwood |first3=Rowan |last4=Swaddle |first4=John P. |last5=Hunt |first5=Gene |date=June 2022 |title=Temporal shifts in ostracode sexual dimorphism from the Late Cretaceous to the late Eocene of the U.S. Coastal Plain |journal=Marine Micropaleontology |language=en |volume=174 |pages=101959 |doi=10.1016/j.marmicro.2020.101959 |doi-access=free |hdl=10400.1/18610 |hdl-access=free }}</ref>

Among [[Decapoda|decapods]], extinction patterns were highly heterogeneous and cannot be neatly attributed to any particular factor. Decapods that inhabited the Western Interior Seaway were especially hard-hit, while other regions of the world's oceans were refugia that increased chances of survival into the Palaeocene.<ref>{{Cite journal |last1=Schweitzer |first1=Carrie E. |last2=Feldmann |first2=Rodney M. |date=June 2023 |title=Selective extinction at the end-Cretaceous and appearance of the modern Decapoda |journal=[[Journal of Crustacean Biology]] |language=en |volume=43 |issue=2 |doi=10.1093/jcbiol/ruad018 |issn=0278-0372}}</ref> Among retroplumid crabs, the genus ''Costacopluma'' was a notable survivor.<ref>{{Cite journal |last1=Hyžný |first1=Matúš |last2=Perrier |first2=Vincent |last3=Robin |first3=Ninon |last4=Martin |first4=Jeremy E. |last5=Sarr |first5=Raphaël |date=January 2016 |title=Costacopluma (Decapoda: Brachyura: Retroplumidae) from the Maastrichtian and Paleocene of Senegal: A survivor of K/Pg events |journal=[[Cretaceous Research]] |language=en |volume=57 |pages=142–156 |doi=10.1016/j.cretres.2015.08.010}}</ref>

Approximately 60% of late-Cretaceous [[Scleractinia|scleractinian]] [[coral]] genera failed to cross the K–Pg boundary into the Paleocene. Further analysis of the coral extinctions shows that approximately 98% of colonial species, ones that inhabit warm, shallow [[Tropics|tropical]] waters, became extinct. The solitary corals, which generally do not form reefs and inhabit colder and deeper (below the [[photic zone]]) areas of the ocean were less impacted by the K–Pg boundary. Colonial coral species rely upon [[symbiosis]] with photosynthetic [[algae]], which collapsed due to the events surrounding the K–Pg boundary,<ref>{{cite journal |author1=Vescsei, A. |author2=Moussavian, E. |s2cid=129296658 |title=Paleocene reefs on the Maiella Platform margin, Italy: An example of the effects of the cretaceous/tertiary boundary events on reefs and carbonate platforms |year=1997 |journal=Facies |volume=36 |issue=1 |pages=123–139 |doi=10.1007/BF02536880 |bibcode=1997Faci...36..123V}}</ref><ref>{{cite journal |author1=Rosen, B. R. |author2=Turnšek, D. |year=1989 |title=Extinction patterns and biogeography of scleractinian corals across the Cretaceous/Tertiary boundary |series=Proceedings of the Fifth International Symposium on Fossil Cnidaria including Archaeocyatha and Spongiomorphs |journal=Memoir of the Association of Australasian Paleontology |location=Brisbane, Queensland |issue=8 |editor1=Jell A |editor2=Pickett JW |pages=355–370}}</ref> but the use of data from coral fossils to support K–Pg extinction and subsequent Paleocene recovery, must be weighed against the changes that occurred in coral ecosystems through the K–Pg boundary.<ref name="MacLeod" />

Most species of [[brachiopods]], a small [[phylum]] of marine invertebrates, survived the K–Pg extinction event and diversified during the early Paleocene.<ref name="MacLeod" />

The numbers [[Bivalvia|bivalve]] genera exhibited significant diminution after the K–Pg boundary. Entire groups of bivalves, including [[rudists]] (reef-building clams) and [[Inoceramidae|inoceramids]] (giant relatives of modern [[scallop]]s), became extinct at the K–Pg boundary,<ref>{{cite journal |author1=Raup, D. M. |author2=Jablonski, D. |year=1993 |title=Geography of end-Cretaceous marine bivalve extinctions |journal=[[Science (journal)|Science]] |volume=260 |issue=5110 |pages=971–973 |bibcode=1993Sci...260..971R |doi=10.1126/science.11537491 |pmid=11537491}}</ref><ref>{{cite journal |author=MacLeod, K. G. |year=1994 |title=Extinction of Inoceramid Bivalves in Maastrichtian Strata of the Bay of Biscay Region of France and Spain |journal=[[Journal of Paleontology]] |volume=68 |issue=5 |pages=1048–1066 |bibcode=1994JPal...68.1048M |doi=10.1017/S0022336000026652 |s2cid=132641572}}</ref> with the gradual extinction of most inoceramid bivalves beginning well before the K–Pg boundary.<ref name="Marshall">{{cite journal |author1=Marshall, C. R. |author2=Ward, P. D. |year=1996 |title=Sudden and Gradual Molluscan Extinctions in the Latest Cretaceous of Western European Tethys |journal=[[Science (journal)|Science]] |volume=274 |issue=5291 |pages=1360–1363 |bibcode=1996Sci...274.1360M |doi=10.1126/science.274.5291.1360 |pmid=8910273 |s2cid=1837900}}</ref> Deposit feeders were the most common bivalves in the catastrophe's aftermath.<ref>{{Cite journal |last1=Hansen |first1=Thor A. |last2=Farrell |first2=Benjamin R. |last3=Upshaw |first3=Banks |date=Spring 1993 |title=The first 2 million years after the Cretaceous-Tertiary boundary in east Texas: rate and paleoecology of the molluscan recovery |journal=[[Paleobiology (journal)|Paleobiology]] |language=en |volume=19 |issue=2 |pages=251–265 |doi=10.1017/S0094837300015906 |issn=0094-8373}}</ref> Abundance was not a factor that affected whether a bivalve taxon went extinct, according to evidence from North America.<ref>{{Cite journal |last=Lockwood |first=Rowan |date=4 March 2003 |title=Abundance not linked to survival across the end-Cretaceous mass extinction: Patterns in North American bivalves |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |language=en |volume=100 |issue=5 |pages=2478–2482 |doi=10.1073/pnas.0535132100 |doi-access=free |issn=0027-8424 |pmc=151366 |pmid=12601147 }}</ref> Veneroid bivalves developed deeper burrowing habitats as the recovery from the crisis ensued.<ref>{{Cite journal |last=Lockwood |first=Rowan |date=Fall 2004 |title=The K/T event and infaunality: morphological and ecological patterns of extinction and recovery in veneroid bivalves |journal=[[Paleobiology (journal)|Paleobiology]] |language=en |volume=30 |issue=4 |pages=507–521 |doi=10.1666/0094-8373(2004)030<0507:TTEAIM>2.0.CO;2 |issn=0094-8373}}</ref>

[[Image:RudistCretaceousUAE.jpg|thumb|left|alt=bivalve shells seven centimeters across|[[Rudist]] bivalves from the Late Cretaceous of the Omani Mountains, United Arab Emirates. Scale bar is 10&nbsp;mm.]]
Except for [[nautiloid]]s (represented by the modern order [[Nautilida]]) and [[Coleoidea|coleoids]] (which had already [[Genetic divergence|diverged]] into modern [[octopus|octopodes]], [[squid]]s, and [[cuttlefish]]) all other species of the [[mollusca]]n class Cephalopoda became extinct at the K–Pg boundary. These included the ecologically significant [[belemnoidea|belemnoids]], as well as the [[Ammonoidea|ammonoids]], a group of highly diverse, numerous, and widely distributed shelled cephalopods.<ref name=":7" /><ref name=":8" /> The extinction of belemnites enabled surviving cephalopod clades to fill their niches.<ref>{{Cite journal |last1=Iba |first1=Yasuhiro |last2=Mutterlose |first2=Jörg |last3=Tanabe |first3=Kazushige |last4=Sano |first4=Shin-ichi |last5=Misaki |first5=Akihiro |last6=Terabe |first6=Kazunobu |date=1 May 2011 |title=Belemnite extinction and the origin of modern cephalopods 35 m.y. prior to the Cretaceous−Paleogene event |url=http://pubs.geoscienceworld.org/geology/article/39/5/483/130552/Belemnite-extinction-and-the-origin-of-modern |journal=[[Geology (journal)|Geology]] |language=en |volume=39 |issue=5 |pages=483–486 |doi=10.1130/G31724.1 |bibcode=2011Geo....39..483I |issn=1943-2682 |access-date=18 November 2023}}</ref> Ammonite genera became extinct at or near the K–Pg boundary; there was a smaller and slower extinction of ammonite genera prior to the boundary associated with a late Cretaceous marine regression, and a small, gradual reduction in ammonite diversity occurred throughout the very late Cretaceous.<ref name="Marshall" /> Researchers have pointed out that the reproductive strategy of the surviving nautiloids, which rely upon few and larger eggs, played a role in outsurviving their ammonoid counterparts through the extinction event. The ammonoids utilized a planktonic strategy of reproduction (numerous eggs and planktonic larvae), which would have been devastated by the K–Pg extinction event. Additional research has shown that subsequent to this elimination of ammonoids from the global biota, nautiloids began an evolutionary radiation into shell shapes and complexities theretofore known only from ammonoids.<ref name=":7">{{cite journal |author1=Ward, P. D. |author2=Kennedy, W. J. |author3=MacLeod, K. G. |author4=Mount, J. F. |year=1991 |title=Ammonite and inoceramid bivalve extinction patterns in Cretaceous/Tertiary boundary sections of the Biscay region (southwestern France, northern Spain) |journal=[[Geology (journal)|Geology]] |volume=19 |issue=12 |pages=1181–1184 |doi=10.1130/0091-7613(1991)019<1181:AAIBEP>2.3.CO;2 |bibcode=1991Geo....19.1181W }}</ref><ref name=":8">{{cite journal |author1=Harries, P. J. |author2=Johnson, K. R. |author3=Cobban, W. A. |author4=Nichols, D.J. |year=2002 |title=Marine Cretaceous-Tertiary boundary section in southwestern South Dakota: Comment and reply |journal=[[Geology (journal)|Geology]] |volume=30 |issue=10 |pages=954–955 |doi=10.1130/0091-7613(2002)030<0955:MCTBSI>2.0.CO;2 |bibcode=2002Geo....30..954H}}</ref>

Approximately 35% of echinoderm genera became extinct at the K–Pg boundary, although [[taxon|taxa]] that thrived in low-latitude, shallow-water environments during the late Cretaceous had the highest extinction rate. Mid-latitude, deep-water echinoderms were much less affected at the K–Pg boundary. The pattern of extinction points to habitat loss, specifically the drowning of [[carbonate platform]]s, the shallow-water reefs in existence at that time, by the extinction event.<ref>{{cite journal |last1=Neraudeau |first1=Didier |last2=Thierry |first2=Jacques |last3=Moreau |first3=Pierre |title=Variation in echinoid biodiversity during the Cenomanian-early Turonian transgressive episode in Charentes (France) |journal=Bulletin de la Société Géologique de France |date=1 January 1997 |volume=168 |issue=1 |pages=51–61 |url=https://pubs.geoscienceworld.org/sgf/bsgf/article-abstract/168/1/51/122879/Variation-in-echinoid-biodiversity-during-the }}</ref> Atelostomatans were affected by the Lilliput effect.<ref>{{Cite journal |last1=Wiese |first1=Frank |last2=Schlüter |first2=Nils |last3=Zirkel |first3=Jessica |last4=Herrle |first4=Jens O. |last5=Friedrich |first5=Oliver |date=9 August 2023 |editor-last=Carnevale |editor-first=Giorgio |title=A 104-Ma record of deep-sea Atelostomata (Holasterioda, Spatangoida, irregular echinoids) – a story of persistence, food availability and a big bang |journal=[[PLOS ONE]] |language=en |volume=18 |issue=8 |pages=e0288046 |doi=10.1371/journal.pone.0288046 |doi-access=free |issn=1932-6203 |pmc=10411753 |pmid=37556403 }}</ref>

===Terrestrial invertebrates===
Insect damage to the fossilized leaves of [[flowering plant]]s from fourteen sites in North America was used as a proxy for insect diversity across the K–Pg boundary and analyzed to determine the rate of extinction. Researchers found that Cretaceous sites, prior to the extinction event, had rich plant and insect-feeding diversity. During the early Paleocene, flora were relatively diverse with little predation from insects, even 1.7&nbsp;million years after the extinction event.<ref name="Labandieraetal">{{cite journal |author1=Labandeira, Conrad C. |author2=Johnson, Kirk R. |author3=Wilf, Peter |title=Impact of the terminal Cretaceous event on plant–insect associations |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=99 |issue=4 |pages=2061–2066 |year=2002 |doi=10.1073/pnas.042492999 |pmid=11854501 |pmc=122319 |bibcode=2002PNAS...99.2061L |doi-access=free }}</ref><ref>{{cite journal |title=Decoupled plant and insect diversity after the end-Cretaceous extinction |author1=Wilf, P. |author2=Labandeira, C. C. |author3=Johnson, K. R. |author4=Ellis, B. |s2cid=52801127 |year=2006 |journal=[[Science (journal)|Science]] |volume=313 |issue=5790 |pages=1112–1115 |doi=10.1126/science.1129569 |pmid=16931760 |bibcode=2006Sci...313.1112W }}</ref> Studies of the size of the [[ichnotaxon]] ''Naktodemasis bowni'', produced by either cicada nymphs or beetle larvae, over the course of the K-Pg transition show that the [[Lilliput effect]] occurred in terrestrial invertebrates thanks to the extinction event.<ref>{{Cite journal |last1=Wiest |first1=Logan A. |last2=Lukens |first2=William E. |last3=Peppe |first3=Daniel J. |last4=Driese |first4=Steven G. |last5=Tubbs |first5=Jack |date=1 February 2018 |title=Terrestrial evidence for the Lilliput effect across the Cretaceous-Paleogene (K-Pg) boundary |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=491 |pages=161–169 |doi=10.1016/j.palaeo.2017.12.005 |bibcode=2018PPP...491..161W |issn=0031-0182|url=http://paleorxiv.org/9x7du/ }}</ref>

The extinction event produced major changes in Paleogene insect communities. Many groups of ants were present in the Cretaceous, but in the Eocene ants became dominant and diverse, with larger colonies. Butterflies diversified as well, perhaps to take the place of leaf-eating insects wiped out by the extinction. The advanced mound-building termites, [[Termitidae]], also appear to have risen in importance.<ref>{{cite book |author=Grimaldi, David A. |title=Evolution of the Insects |publisher=Cambridge Univ Pr (E) |year=2007 |isbn=978-0-511-12388-7}}</ref>

===Fish===
There are fossil records of [[Gnathostomata|jawed fishes]] across the K–Pg boundary, which provide good evidence of extinction patterns of these classes of marine vertebrates. While the deep-sea realm was able to remain seemingly unaffected, there was an equal loss between the open marine [[apex predator]]s and the [[durophagous]] [[demersal]] feeders on the continental shelf. Within [[Chondrichthyes|cartilaginous fish]], approximately 7 out of the 41&nbsp;families of [[Neoselachii|neoselachians]] (modern [[sharks]], skates, and rays) disappeared after this event and [[Batoidea|batoids]] (skates and rays) lost nearly all the identifiable species, while more than 90% of [[teleostei|teleost fish]] (bony fish) families survived.<ref name=":0">{{cite journal |last1=Kriwet |first1=Jürgen |last2=Benton |first2=Michael J. |date=2004 |title=Neoselachian (Chondrichthyes, Elasmobranchii) Diversity across the Cretaceous–Tertiary Boundary |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=214 |issue=3 |pages=181–194 |bibcode=2004PPP...214..181K |doi=10.1016/j.palaeo.2004.02.049}}</ref><ref>{{cite book |last=Patterson |first=C. |title=The Fossil Record |publisher=Springer |year=1993 |isbn=978-0-412-39380-8 |editor=Benton, M. J. |volume=2 |pages=621–656 |contribution=Osteichthyes: Teleostei}}</ref>

In the Maastrichtian age, 28&nbsp;[[shark]] families and 13&nbsp;batoid families thrived, of which 25 and 9, respectively, survived the K–T boundary event. Forty-seven of all neoselachian genera cross the K–T boundary, with 85% being sharks. Batoids display with 15%, a comparably low survival rate.<ref name=":0" /><ref>{{cite journal |last=Noubhani |first=Abdelmajid |date=2010 |title=The Selachians' faunas of the Moroccan phosphate deposits and the K-T mass extinctions |journal=[[Historical Biology]] |volume=22 |issue=1–3 |pages=71–77 |bibcode=2010HBio...22...71N |doi=10.1080/08912961003707349 |s2cid=129579498}}</ref> Among elasmobranchs, those species that inhabited higher latitudes and lived pelagic lifestyles were more likely to survive, whereas epibenthic lifestyles and durophagy were strongly associated with the likelihood of perishing during the extinction event.<ref>{{cite journal |last1=Guinot |first1=Guillaume |last2=Condamine |first2=Fabien L. |date=23 February 2023 |title=Global impact and selectivity of the Cretaceous-Paleogene mass extinction among sharks, skates, and rays |journal=[[Science (journal)|Science]] |volume=379 |issue=6634 |pages=802–806 |bibcode=2023Sci...379..802G |doi=10.1126/science.abn2080 |pmid=36821692 |s2cid=257103123|url=https://hal.science/hal-04262391/file/Manuscrit%20Guinot%20%26%20Condamine%202023.pdf }}</ref>

There is evidence of a mass extinction of [[Osteichthyes|bony fishes]] at a fossil site immediately above the K–Pg boundary layer on [[Seymour Island]] near [[Antarctica]], apparently precipitated by the K–Pg extinction event;<ref>{{cite journal |author=Zinsmeister, W. J. |date=1 May 1998 |title=Discovery of fish mortality horizon at the K–T boundary on Seymour Island: Re-evaluation of events at the end of the Cretaceous |journal=[[Journal of Paleontology]] |volume=72 |issue=3 |pages=556–571 |bibcode=1998JPal...72..556Z |doi=10.1017/S0022336000024331 |s2cid=132206016}}</ref><ref>{{Cite journal |last1=Cione |first1=Alberto L. |last2=Santillana |first2=Sergio |last3=Gouiric-Cavalli |first3=Soledad |last4=Acosta Hospitaleche |first4=Carolina |last5=Gelfo |first5=Javier N. |last6=López |first6=Guillermo M. |last7=Reguero |first7=Marcelo |date=May 2018 |title=Before and after the K/Pg extinction in West Antarctica: New marine fish records from Marambio (Seymour) Island |journal=[[Cretaceous Research]] |language=en |volume=85 |pages=250–265 |doi=10.1016/j.cretres.2018.01.004 |hdl=11336/99687 |url=http://sedici.unlp.edu.ar/handle/10915/147537 |hdl-access=free }}</ref> the marine and freshwater environments of fishes mitigated the environmental effects of the extinction event.<ref name="Robertson" /> The result was Patterson's Gap, a period in the earliest part of the Cenozoic of decreased acanthomorph diversity,<ref>{{Cite journal |last1=Friedman |first1=Matt |last2=V. Andrews |first2=James |last3=Saad |first3=Hadeel |last4=El-Sayed |first4=Sanaa |date=16 June 2023 |title=The Cretaceous–Paleogene transition in spiny-rayed fishes: surveying "Patterson's Gap" in the acanthomorph skeletal record André Dumont medalist lecture 2018 |url=https://popups.uliege.be/1374-8505/index.php?id=7048 |journal=Geologica Belgica |language=en |doi=10.20341/gb.2023.002 |issn=1374-8505 |access-date=22 August 2024|doi-access=free }}</ref> although acanthomorphs diversified rapidly after the extinction.<ref>{{Cite journal |last1=Alfaro |first1=Michael E. |last2=Faircloth |first2=Brant C. |last3=Harrington |first3=Richard C. |last4=Sorenson |first4=Laurie |last5=Friedman |first5=Matt |last6=Thacker |first6=Christine E. |last7=Oliveros |first7=Carl H. |last8=Černý |first8=David |last9=Near |first9=Thomas J. |date=12 March 2018 |title=Explosive diversification of marine fishes at the Cretaceous–Palaeogene boundary |url=https://www.nature.com/articles/s41559-018-0494-6 |journal=[[Nature Ecology & Evolution]] |language=en |volume=2 |issue=4 |pages=688–696 |doi=10.1038/s41559-018-0494-6 |pmid=29531346 |issn=2397-334X |access-date=22 August 2024}}</ref> Teleost fish diversified explosively after the mass extinction, filling the niches left vacant by the extinction. Groups appearing in the Paleocene and Eocene epochs include billfish, tunas, eels, and flatfish.<ref name="Friedman, M. 2010" />

=== Amphibians ===
There is limited evidence for extinction of amphibians at the K–Pg boundary. A study of fossil vertebrates across the K–Pg boundary in [[Montana]] concluded that no species of amphibian became extinct.<ref name="Archibald">{{cite book |author1=Archibald, J. D. |author2=Bryant, L. J. |year=1990 |chapter=Differential Cretaceous–Tertiary extinction of nonmarine vertebrates; evidence from northeastern Montana |title=Global Catastrophes in Earth History: an Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality |editor1=Sharpton, V.L. |editor2=Ward, P.D. |publisher=Geological Society of America |series=Special Paper |volume= 247 |pages=549–562 |doi=10.1130/spe247-p549 |isbn=978-0-8137-2247-4}}</ref> Yet there are several species of Maastrichtian amphibian, not included as part of this study, which are unknown from the Paleocene. These include the frog ''[[Theatonius|Theatonius lancensis]]''<ref>{{cite journal |last1=Estes |first1= R. |year= 1964 |title=Fossil vertebrates from the late Cretaceous Lance formation, eastern Wyoming |journal=University of California Publications, Department of Geological Sciences |volume=49 |pages=1–180}}</ref> and the [[Albanerpetontidae|albanerpetontid]] ''[[Albanerpeton|Albanerpeton galaktion]]'';<ref>{{cite journal |author= Gardner, J. D. |year=2000 |title=Albanerpetontid amphibians from the upper Cretaceous (Campanian and Maastrichtian) of North America |journal=[[Geodiversitas]] |volume=22 |issue=3 |pages=349–388}}</ref> therefore, some amphibians do seem to have become extinct at the boundary. The relatively low levels of extinction seen among amphibians probably reflect the low extinction rates seen in freshwater animals.<ref name="major" /> Following the mass extinction, frogs radiated substantially, with 88% of modern anuran diversity being traced back to three lineages of frogs that evolved after the cataclysm.<ref>{{Cite journal |last1=Feng |first1=Yan-Jie |last2=Blackburn |first2=David C. |last3=Liang |first3=Dan |last4=Hillis |first4=David M. |last5=Wake |first5=David B. |last6=Cannatella |first6=David C. |last7=Zhang |first7=Peng |date=18 July 2017 |title=Phylogenomics reveals rapid, simultaneous diversification of three major clades of Gondwanan frogs at the Cretaceous–Paleogene boundary |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |language=en |volume=114 |issue=29 |pages=E5864–E5870 |doi=10.1073/pnas.1704632114 |doi-access=free |issn=0027-8424 |pmc=5530686 |pmid=28673970 }}</ref>

=== Reptiles ===

==== Choristoderes ====
The [[Choristodera|choristoderes]] (a group of semi-aquatic diapsids of uncertain position) survived across the K–Pg boundary<ref name="MacLeod" /> subsequently becoming extinct in the [[Miocene]].<ref name="EK05">{{cite journal |last1=Evans |first1=Susan E. |last2=Klembara |first2=Jozef |year=2005 |title=A choristoderan reptile (Reptilia: Diapsida) from the Lower Miocene of northwest Bohemia (Czech Republic) |journal=[[Journal of Vertebrate Paleontology]] |volume=25 |issue=1 |pages=171–184 |doi=10.1671/0272-4634(2005)025[0171:ACRRDF]2.0.CO;2 |s2cid=84097919}}</ref> The gharial-like choristodere genus ''[[Champsosaurus]]''{{'}} palatal teeth suggest that there were dietary changes among the various species across the K–Pg event.<ref>{{cite journal |last1=Matsumoto |first1=Ryoko |last2=Evans |first2=Susan E. |date=November 2015 |title=Morphology and function of the palatal dentition in Choristodera |journal=[[Journal of Anatomy]] |volume=228 |issue=3 |pages=414–429 |doi=10.1111/joa.12414 |pmc=5341546 |pmid=26573112}}</ref>

==== Turtles ====
More than 80% of Cretaceous [[turtle]] species passed through the K–Pg boundary. All six turtle families in existence at the end of the Cretaceous survived into the [[Paleogene]] and are represented by living species.<ref name="Novacek">{{cite journal |title=100&nbsp;million years of land vertebrate evolution: The Cretaceous-early Tertiary transition |author=Novacek, M. J. |journal=[[Annals of the Missouri Botanical Garden]] |volume=86 |issue=2 |year=1999 |pages=230–258 |doi=10.2307/2666178 |jstor=2666178|url=https://www.biodiversitylibrary.org/part/28619 }}</ref> Analysis of turtle survivorship in the Hell Creek Formation shows a minimum of 75% of turtle species survived.<ref>{{cite book |last1=Holroyd |first1=Patricia A. |last2=Wilson |first2=Gregory P. |last3=Hutchinson |first3=J. Howard |editor-last1=Wilson |editor-first1=Gregory P. |editor-last2=Clemens |editor-first2=William A. |editor-last3=Horner |editor-first3=John R. |editor-last4=Hartman |editor-first4=Joseph H. |date=2013 |title=Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas |chapter=Temporal changes within the latest Cretaceous and early Paleogene turtle faunas of northeastern Montana |chapter-url=https://books.google.com/books?id=chKDAgAAQBAJ&dq=cretaceous+paleogene+extinction+turtles&pg=PA299 |location=Boulder, CO |publisher=Geological Society of America |pages=299–312 |isbn=978-0-8137-2503-1}}</ref> Following the extinction event, turtle diversity exceeded pre-extinction levels in the Danian of North America, although in South America it remained diminished.<ref>{{Cite journal |last1=Cleary |first1=Terri J. |last2=Benson |first2=Roger B. J. |last3=Holroyd |first3=Patricia A. |last4=Barrett |first4=Paul M. |date=10 May 2020 |editor-last=Mannion |editor-first=Philip |title=Tracing the patterns of non-marine turtle richness from the Triassic to the Palaeogene: from origin to global spread |journal=[[Palaeontology (journal)|Palaeontology]] |language=en |volume=63 |issue=5 |pages=753–774 |doi=10.1111/pala.12486 |doi-access=free |issn=0031-0239}}</ref> European turtles likewise recovered rapidly following the mass extinction.<ref>{{Cite journal |last=Pérez-García |first=Adán |date=30 January 2020 |title=Surviving the Cretaceous-Paleogene mass extinction event: A terrestrial stem turtle in the Cenozoic of Laurasia |journal=[[Scientific Reports]] |language=en |volume=10 |issue=1 |pages=1489 |doi=10.1038/s41598-020-58511-8 |pmid=32001765 |issn=2045-2322|pmc=6992736 }}</ref>

====Lepidosauria====
The [[rhynchocephalia]]ns which were a globally distributed and diverse group of lepidosaurians during the early [[Mesozoic]], had begun to decline by the mid-Cretaceous, although they remained successful in the Late Cretaceous of southern [[South America]].<ref>{{cite journal |author1=Apesteguía, Sebastián |author2=Novas, Fernando E. |s2cid=4425130 |year=2003 |title=Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana |journal=Nature |volume=425 |issue=6958 |pages=609–612 |doi=10.1038/nature01995 |pmid=14534584 |bibcode=2003Natur.425..609A}}</ref> They are represented today by a single species, the [[tuatara]] (''Sphenodon punctatus'') found in [[Biodiversity of New Zealand|New Zealand]].<ref>{{cite book |last=Lutz |first=D. |year=2005 |title=Tuatara: A living fossil |publisher=DIMI Press |isbn=978-0-931625-43-5}}</ref> Outside of New Zealand, one rhynchocephalian is known to have crossed the K-Pg boundary, ''[[Kawasphenodon|Kawasphenodon peligrensis]],'' known from the earliest Paleocene (Danian) of Patagonia.<ref name=":12">{{Cite journal |last1=Apesteguía |first1=Sebastián |last2=Gómez |first2=Raúl O. |last3=Rougier |first3=Guillermo W. |date=2014-10-07 |title=The youngest South American rhynchocephalian, a survivor of the K/Pg extinction |url= |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=281 |issue=1792 |pages=20140811 |doi=10.1098/rspb.2014.0811 |issn=0962-8452 |pmc=4150314 |pmid=25143041}}</ref>

The order [[Squamata]] comprising lizards and snakes first diversified during the Jurassic and continued to diversify throughout the Cretaceous.<ref>{{Cite journal |last1=Herrera-Flores |first1=Jorge A. |last2=Stubbs |first2=Thomas L. |last3=Benton |first3=Michael J. |date=March 2021 |title=Ecomorphological diversification of squamates in the Cretaceous |journal=Royal Society Open Science |language=en |volume=8 |issue=3 |pages=rsos.201961, 201961 |doi=10.1098/rsos.201961 |issn=2054-5703 |pmc=8074880 |pmid=33959350|bibcode=2021RSOS....801961H }}</ref> They are currently the most successful and diverse group of living reptiles, with more than 10,000&nbsp;extant species. The only major group of terrestrial lizards to go extinct at the end of the Cretaceous were the [[Polyglyphanodontia|polyglyphanodontians]], a diverse group of mainly herbivorous lizards known predominantly from the Northern Hemisphere<ref>{{Cite journal |last1=Xing |first1=Lida |last2=Niu |first2=Kecheng |last3=Evans |first3=Susan E. |date=January 2023 |title=A new polyglyphanodontian lizard with a complete lower temporal bar from the Upper Cretaceous of southern China |journal=Journal of Systematic Palaeontology |language=en |volume=21 |issue=1 |doi=10.1080/14772019.2023.2281494 |issn=1477-2019|doi-access=free |bibcode=2023JSPal..2181494X }}</ref> The [[mosasaur]]s, a diverse group of large predatory marine reptiles, also became extinct. Fossil evidence indicates that squamates generally suffered very heavy losses in the K–Pg event, only recovering 10&nbsp;million years after it. The extinction of Cretaceous lizards and snakes may have led to the evolution of modern groups such as iguanas, monitor lizards, and boas.<ref name="Longrich, N. R. 2012" /> The diversification of crown group snakes has been linked to the biotic recovery in the aftermath of the K-Pg extinction event.<ref>{{cite journal |last1=Klein |first1=Catherine G. |last2=Pisani |first2=Davide |last3=Field |first3=Daniel J. |last4=Lakin |first4=Rebecca |last5=Wills |first5=Matthew A. |last6=Longrich |first6=Nicholas R. |date=14 September 2021 |title=Evolution and dispersal of snakes across the Cretaceous-Paleogene mass extinction |journal=[[Nature Communications]] |volume=12 |issue=1 |page=5335 |bibcode=2021NatCo..12.5335K |doi=10.1038/s41467-021-25136-y |pmc=8440539 |pmid=34521829}}</ref> Pan-Gekkotans weathered the extinction event well, with multiple lineages likely surviving.<ref>{{Cite journal |last1=Čerňanský |first1=Andrej |last2=Daza |first2=Juan |last3=Tabuce |first3=Rodolphe |last4=Saxton |first4=Elizabeth |last5=Vidalenc |first5=Dominique |date=December 2023 |title=An early Eocene pan-gekkotan from France could represent an extra squamate group that survived the K-Pg extinction |url=https://www.app.pan.pl/article/item/app010832023.html |journal=[[Acta Palaeontologica Polonica]] |volume=68 |doi=10.4202/app.01083.2023 |access-date=22 August 2024}}</ref>

====Marine reptiles====
'''∆'''<sup>44/42</sup>Ca values indicate that prior to the mass extinction, marine reptiles at the top of food webs were feeding on only one source of calcium, suggesting their populations exhibited heightened vulnerability to extinctions at the terminus of the Cretaceous.<ref>{{Cite journal |last1=Martin |first1=Jeremy E. |last2=Vincent |first2=Peggy |last3=Tacail |first3=Théo |last4=Khaldoune |first4=Fatima |last5=Jourani |first5=Essaid |last6=Bardet |first6=Nathalie |last7=Balter |first7=Vincent |date=5 June 2017 |title=Calcium Isotopic Evidence for Vulnerable Marine Ecosystem Structure Prior to the K/Pg Extinction |journal=[[Current Biology]] |volume=27 |issue=11 |pages=1641–1644.e2 |doi=10.1016/j.cub.2017.04.043 |issn=0960-9822 |doi-access=free |pmid=28552352 }}</ref> Along with the aforementioned mosasaurs, [[Plesiosauria|plesiosaurs]], represented by the families [[Elasmosauridae]] and [[Polycotylidae]], became extinct during the event.<ref>{{cite journal |last1=D'Hondt |first1=Steven |date=17 August 2005 |title=Consequences of the Cretaceous/Paleogene Mass Extinction for Marine Ecosystems |journal=[[Annual Review of Ecology, Evolution, and Systematics]] |volume=36 |pages=295–317 |doi=10.1146/annurev.ecolsys.35.021103.105715 |s2cid=86073650}}</ref><ref name="ChatterjeeSmall">{{cite journal |author1=Chatterjee, S. |author2=Small, B. J. |s2cid=140639013 |title=New plesiosaurs from the Upper Cretaceous of Antarctica |journal=Geological Society of London |series=Special Publications |volume=47 |issue=1 |pages=197–215 |year=1989 |doi=10.1144/GSL.SP.1989.047.01.15 |bibcode=1989GSLSP..47..197C }}</ref><ref>{{cite journal |author=O'Keefe, F. R. |year=2001 |title=A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia) |journal=Acta Zoologica Fennica |volume=213 |pages=1–63}}</ref><ref>{{Cite journal |last=O'Gorman |first=José P. |date=December 2022 |title=Polycotylidae (Sauropterygia, Plesiosauria) from the La Colonia Formation, Patagonia, Argentina: Phylogenetic affinities of Sulcusuchus erraini and the Late Cretaceous circum-pacific polycotylid diversity |journal=[[Cretaceous Research]] |language=en |volume=140 |pages=105339 |s2cid=251749728 |bibcode=2022CrRes.14005339O |doi=10.1016/j.cretres.2022.105339}}</ref> The [[ichthyosaur]]s had disappeared from fossil record tens of millions of years prior to the K-Pg extinction event.<ref>{{cite journal |last1=Fischer |first1=Valentin |last2=Bardet |first2=Nathalie |last3=Benson |first3=Roger B. J. |last4=Arkhangelsky |first4=Maxim S. |last5=Friedman |first5=Matt |title=Extinction of fish-shaped marine reptiles associated with reduced evolutionary rates and global environmental volatility |journal=[[Nature Communications]] |date=2016 |volume=7 |issue=1 |page=10825 |doi=10.1038/ncomms10825 |pmid=26953824 |pmc=4786747 |bibcode=2016NatCo...710825F |doi-access=free }}</ref>

====Crocodyliforms====

Ten families of crocodilians or their close relatives are represented in the Maastrichtian fossil records, of which five died out prior to the K–Pg boundary.<ref>{{cite journal |title=Calibration age and quartet divergence date estimation |author=Brochu, C. A. |s2cid=198156470 |year=2004 |journal=[[Evolution (journal)|Evolution]] |volume=58 |issue=6 |pages=1375–1382 |doi=10.1554/03-509 |pmid=15266985}}</ref> Five families have both Maastrichtian and Paleocene fossil representatives. All of the surviving families of [[Crocodyliformes|crocodyliforms]] inhabited freshwater and terrestrial environments—except for the [[Dyrosauridae]], which lived in freshwater and marine locations. Approximately 50% of crocodyliform representatives survived across the K–Pg boundary, the only apparent trend being that no large crocodiles survived.<ref name="MacLeod" /> Crocodyliform survivability across the boundary may have resulted from their aquatic niche and ability to burrow, which reduced susceptibility to negative environmental effects at the boundary.<ref name="Robertson">{{cite journal |title=Survival in the first hours of the Cenozoic |author1=Robertson, D. S. |author2=McKenna, M. C. |author3=Toon, O. B. |author4=Hope, S. |author5=Lillegraven, J. A. |display-authors=3 |s2cid=44010682 |journal=[[Geological Society of America Bulletin]] |year=2004 |volume=116 |issue=5–6 |pages=760–768 |doi=10.1130/B25402.1 |bibcode=2004GSAB..116..760R |url=https://pdfs.semanticscholar.org/8d43/36c3d3e40d27390e37941e4affe0cff84bb2.pdf |archive-url=https://web.archive.org/web/20190507051856/https://pdfs.semanticscholar.org/8d43/36c3d3e40d27390e37941e4affe0cff84bb2.pdf  |archive-date=2019-05-07 }}</ref> Jouve and colleagues suggested in 2008 that juvenile marine crocodyliforms lived in freshwater environments as do modern marine [[crocodile]] juveniles, which would have helped them survive where other [[marine reptile]]s became extinct; freshwater environments were not so strongly affected by the K–Pg extinction event as marine environments were.<ref name="SJetal08">{{cite journal |author1=Jouve, S. |author2=Bardet, N. |author3=Jalil, N.-E. |author4=Suberbiola, X. P. |author5=Bouya, B. |author6=Amaghzaz, M. |year=2008 |title=The oldest African crocodylian: phylogeny, paleobiogeography, and differential survivorship of marine reptiles through the Cretaceous-Tertiary boundary |journal=[[Journal of Vertebrate Paleontology]] |volume=28 |issue=2 |pages=409–421 |doi=10.1671/0272-4634(2008)28[409:TOACPP]2.0.CO;2 |s2cid=86503283 |url=http://doc.rero.ch/record/16384/files/PAL_E3543.pdf }}</ref> Among the terrestrial clade [[Notosuchia]], only the family [[Sebecidae]] survived; the exact reasons for this pattern are not known.<ref>{{Cite journal |last1=Aubier |first1=Paul |last2=Jouve |first2=Stéphane |last3=Schnyder |first3=Johann |last4=Cubo |first4=Jorge |date=20 February 2023 |editor-last=Mannion |editor-first=Philip |title=Phylogenetic structure of the extinction and biotic factors explaining differential survival of terrestrial notosuchians at the Cretaceous–Palaeogene crisis |journal=[[Palaeontology (journal)|Palaeontology]] |language=en |volume=66 |issue=1 |page=12638 |doi=10.1111/pala.12638 |issn=0031-0239 |doi-access=free |bibcode=2023Palgy..6612638A }}</ref> Sebecids were large terrestrial predators, are known from the Eocene of Europe, and would survive in South America into the Miocene.<ref>{{Cite journal |last1=Martin |first1=Jeremy E. |last2=Pochat-Cottilloux |first2=Yohan |last3=Laurent |first3=Yves |last4=Perrier |first4=Vincent |last5=Robert |first5=Emmanuel |last6=Antoine |first6=Pierre-Olivier |date=2022-10-28 |title=Anatomy and phylogeny of an exceptionally large sebecid (Crocodylomorpha) from the middle Eocene of southern France |journal=Journal of Vertebrate Paleontology |language=en |volume=42 |issue=4 |doi=10.1080/02724634.2023.2193828 |bibcode=2022JVPal..42E3828M |s2cid=258361595 |issn=0272-4634}}</ref> Tethysuchians radiated explosively after the extinction event.<ref>{{Cite journal |last1=Forêt |first1=Tom |last2=Aubier |first2=Paul |last3=Jouve |first3=Stéphane |last4=Cubo |first4=Jorge |date=23 April 2024 |title=Biotic and abiotic factors and the phylogenetic structure of extinction in the evolution of Tethysuchia |journal=[[Paleobiology (journal)|Paleobiology]] |language=en |volume=50 |issue=2 |pages=285–307 |doi=10.1017/pab.2024.5 |issn=0094-8373}}</ref>

====Pterosaurs====
Two families of pterosaurs, [[Azhdarchidae]] and [[Nyctosauridae]], were definitely present in the Maastrichtian, and they likely became extinct at the K–Pg boundary. Several other pterosaur lineages may have been present during the Maastrichtian, such as the [[Eupterodactyloidea|ornithocheirids]], [[Pteranodontidae|pteranodontids]], a possible [[Tapejaridae|tapejarid]], a possible [[Thalassodrominae|thalassodromid]] and a basal toothed taxon of uncertain affinities, though they are represented by fragmentary remains that are difficult to assign to any given group.<ref>{{cite journal |author1=Company, J. |author2=Ruiz-Omeñaca, J. I. |author3=Pereda Suberbiola, X. |s2cid=73638590 |year=1999 |title=A long-necked pterosaur (Pterodactyloidea, Azhdarchidae) from the upper Cretaceous of Valencia, Spain |journal=Geologie en Mijnbouw |volume=78 |issue=3 |pages=319–333|doi=10.1023/A:1003851316054}}</ref><ref>{{cite journal |author1=Barrett, P. M. |author2=Butler, R. J. |author3=Edwards, N. P. |author4=Milner, A. R. |year=2008 |title=Pterosaur distribution in time and space: an atlas |url=http://epub.ub.uni-muenchen.de/12007/1/zitteliana_2008_b28_05.pdf |journal=Zitteliana |volume=28 |pages=61–107 |access-date=2015-08-31 |archive-url=https://web.archive.org/web/20170806150333/https://epub.ub.uni-muenchen.de/12007/1/zitteliana_2008_b28_05.pdf |archive-date=2017-08-06 |url-status=live}}</ref> While this was occurring, modern birds were undergoing diversification; traditionally it was thought that they replaced archaic birds and pterosaur groups, possibly due to direct competition, or they simply filled empty niches,<ref name="Robertson" /><ref>{{cite journal |last1=Slack|first1=K. E. |last2=Jones|first2=C. M. |last3=Ando|first3=T. |last4=Harrison|first4=G. L. |last5=Fordyce|first5=R. E. |last6=Arnason|first6=U. |last7=Penny|first7=D. |year=2006 |title=Early Penguin Fossils, Plus Mitochondrial Genomes, Calibrate Avian Evolution |journal=[[Molecular Biology and Evolution]] |volume=23 |issue=6 |pages=1144–1155 |doi=10.1093/molbev/msj124 |pmid=16533822|doi-access=free}}</ref><ref name="PennyPhillips">{{cite journal |author1=Penny, D. |author2=Phillips, M. J. |year=2004 |title=The rise of birds and mammals: Are microevolutionary processes sufficient for macroevolution? |journal=[[Trends in Ecology and Evolution]] |volume=19 |issue=10 |pages=516–522 |doi=10.1016/j.tree.2004.07.015 |pmid=16701316 |url=http://doc.rero.ch/record/14569/files/PAL_E1781.pdf }}</ref> but there is no correlation between pterosaur and avian diversities that are conclusive to a competition hypothesis,<ref>{{cite journal |author1=Butler, Richard J. |author2=Barrett, Paul M. |author3=Nowbath, Stephen |author4=Upchurch, Paul |year=2009 |s2cid=84324007 |title=Estimating the effects of sampling biases on pterosaur diversity patterns: Implications for hypotheses of bird / pterosaur competitive replacement |journal=[[Paleobiology (journal)|Paleobiology]] |volume=35 |issue=3 |pages=432–446 |doi=10.1666/0094-8373-35.3.432 |bibcode=2009Pbio...35..432B}}</ref> and small pterosaurs were present in the Late Cretaceous.<ref>{{cite journal |author1=Prondvai, E. |author2=Bodor, E. R. |author3=Ösi, A. |s2cid=85673254 |year=2014 |title=Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity |journal=[[Paleobiology (journal)|Paleobiology]] |volume=40 |issue=2 |pages=288–321 |doi=10.1666/13030 |bibcode=2014Pbio...40..288P |url=http://real.mtak.hu/21860/1/Prondvai_et_al.2014_reposit1_u_110445.946242.pdf }}</ref> At least some niches previously held by birds were reclaimed by pterosaurs prior to the K–Pg event.<ref>{{cite journal |last1=Longrich |first1=N. R. |last2=Martill |first2=D. M. |last3=Andres |first3=B. |year=2018 |title=Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary |journal=PLOS Biology |volume=16 |issue=3 |pages=e2001663 |doi=10.1371/journal.pbio.2001663 |pmid=29534059 |pmc=5849296 |doi-access=free }}</ref>

====Non-avian dinosaurs====
[[File:Tyrannosaurus Rex Holotype.jpg|thumb|alt=Tyrannosaurus skeleton in museum display|''[[Tyrannosaurus]]'' was among the dinosaurs living on Earth before the extinction.]]

Scientists agree that all non-avian dinosaurs became extinct at the K–Pg boundary. The dinosaur fossil record has been interpreted to show both a decline in diversity and no decline in diversity during the last few million years of the Cretaceous, and it may be that the quality of the dinosaur fossil record is simply not good enough to permit researchers to distinguish between the options.<ref name="AF04">{{cite book |first1=Archibald |last1=David |first2=David |last2=Fastovsky |editor=Weishampel, David B. |editor2=Dodson, Peter |editor3=Osmólska, Halszka |title=The Dinosauria |edition=2nd |year=2004 |publisher=University of California Press |location=Berkeley |isbn=978-0-520-24209-8 |pages=672–684 |chapter=Dinosaur extinction |chapter-url=http://www.bio.sdsu.edu/faculty/archibald/ArchFast.pdf}}</ref> There is no evidence that late Maastrichtian non-avian dinosaurs could burrow, swim, or dive, which suggests they were unable to shelter themselves from the worst parts of any environmental stress that occurred at the K–Pg boundary. It is possible that small dinosaurs (other than birds) did survive, but they would have been deprived of food, as herbivorous dinosaurs would have found plant material scarce and carnivores would have quickly found prey in short supply.<ref name="Robertson" />

The growing consensus about the endothermy of dinosaurs (see [[physiology of dinosaurs|dinosaur physiology]]) helps to understand their full extinction in contrast with their close relatives, the crocodilians. Ectothermic ("cold-blooded") crocodiles have very limited needs for food (they can survive several months without eating), while endothermic ("warm-blooded") animals of similar size need much more food to sustain their faster metabolism. Thus, under the circumstances of food chain disruption previously mentioned, non-avian dinosaurs died out,<ref name="autogenerated347" /> while some crocodiles survived. In this context, the survival of other endothermic animals, such as some birds and mammals, could be due, among other reasons, to their smaller needs for food, related to their small size at the extinction epoch.<ref name="springerlink.com">{{cite book |author1=Ocampo, A. |author2=Vajda, V. |author3=Buffetaut, E. |chapter=Unravelling the Cretaceous–Paleogene (K–T) turnover, evidence from flora, fauna and geology in biological processes associated with impact events |editor1=Cockell, C. |editor2=Gilmour, I. |editor3=Koeberl, C. |title=Biological Processes Associated with Impact Events |url=https://archive.org/details/biologicalproces00cock |url-access=limited |publisher=SpringerLink |year=2006 |pages=[https://archive.org/details/biologicalproces00cock/page/n211 197]–219 |doi=10.1007/3-540-25736-5_9 |isbn=978-3-540-25735-6}}</ref> Prolonged cold is unlikely to have been a reason for the extinction of non-avian dinosaurs given the adaptations of many dinosaurs to cold environments.<ref>{{Cite journal |last=Buffetaut |first=Eric |date=18 November 2004 |title=Polar dinosaurs and the question of dinosaur extinction: a brief review |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=214 |issue=3 |pages=225–231 |doi=10.1016/j.palaeo.2004.02.050}}</ref>

Whether the extinction occurred gradually or suddenly has been debated, as both views have support from the fossil record. A highly informative sequence of dinosaur-bearing rocks from the K–Pg boundary is found in western North America, particularly the late Maastrichtian-age [[Hell Creek Formation]] of [[Montana]].<ref>{{cite journal |last1=Fastovsky |first1=David E. |last2=Bercovici |first2=Antoine |date=January 2016 |title=The Hell Creek Formation and its contribution to the Cretaceous–Paleogene extinction: A short primer |journal=[[Cretaceous Research]] |volume=57 |pages=368–390 |bibcode=2016CrRes..57..368F |doi=10.1016/j.cretres.2015.07.007 |doi-access=free}}</ref> Comparison with the older [[Judith River Formation]] (Montana) and [[Dinosaur Park Formation]] ([[Alberta]]), which both date from approximately 75&nbsp;Ma, provides information on the changes in dinosaur populations over the last 10&nbsp;million years of the Cretaceous. These fossil beds are geographically limited, covering only part of one continent.<ref name="AF04" /> The middle–late Campanian formations show a greater diversity of dinosaurs than any other single group of rocks. The late Maastrichtian rocks contain the largest members of several major clades: ''[[Tyrannosaurus]]'', ''[[Ankylosaurus]]'', ''[[Pachycephalosaurus]]'', ''[[Triceratops]]'', and ''[[Torosaurus]]'',  which suggests food was plentiful immediately prior to the extinction.<ref name="Dodson">{{cite book |last=Dodson |first=Peter |title=The Horned Dinosaurs: A Natural History |publisher=Princeton University Press |year=1996 |isbn=978-0-691-05900-6 |location=Princeton, NJ |url=https://archive.org/details/horneddinosaursn00dods_0 |pages=[https://archive.org/details/horneddinosaursn00dods_0/page/279 279–281] |author-link=Peter Dodson |url-access=registration}}</ref> A study of 29&nbsp;fossil sites in Catalan [[Pyrenees]] of Europe in 2010 supports the view that dinosaurs there had great diversity until the asteroid impact, with more than 100&nbsp;living species.<ref>{{cite journal |author1=Rieraa, V. |author2=Marmib, J. |author3=Omsa, O. |author4=Gomez, B.
|title=Orientated plant fragments revealing tidal palaeocurrents in the Fumanya mudflat (Maastrichtian, southern Pyrenees): Insights in palaeogeographic reconstructions |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=288 |issue=1–4 |pages=82–92 |date=March 2010 |doi=10.1016/j.palaeo.2010.01.037|bibcode=2010PPP...288...82R}}</ref> More recent research indicates that this figure is obscured by [[Taphonomy|taphonomic]] biases and the sparsity of the continental fossil record. The results of this study, which were based on estimated real global biodiversity, showed that between 628 and 1,078&nbsp;non-avian dinosaur species were alive at the end of the Cretaceous and underwent sudden extinction after the Cretaceous–Paleogene extinction event.<ref>{{cite journal |author=le Loeuff, J. |year=2012 |title=Paleobiogeography and biodiversity of Late Maastrichtian dinosaurs: How many dinosaur species became extinct at the Cretaceous-Tertiary boundary? |journal=Bulletin de la Société Géologique de France |volume=183 |issue=6 |pages=547–559 |doi=10.2113/gssgfbull.183.6.547}}</ref> Alternatively, interpretation based on the fossil-bearing rocks along the [[Red Deer River]] in Alberta, Canada, supports the gradual extinction of non-avian dinosaurs; during the last 10&nbsp;million years of the Cretaceous layers there, the number of dinosaur species seems to have decreased from about 45 to approximately 12. Other scientists have made the same assessment following their research.<ref>{{cite journal |author1=Ryan, M. J. |author2=Russell, A. P. |author3=Eberth, D. A. |author4=Currie, P. J. |title=The taphonomy of a Centrosaurus (Ornithischia: Ceratopsidae) bone bed from the Dinosaur Park formation (Upper Campanian), Alberta, Canada, with comments on cranial ontogeny |journal=[[PALAIOS]] |volume=16 |issue=5 |pages=482–506 |year=2001 |doi=10.1669/0883-1351(2001)016<0482:ttoaco>2.0.co;2 |bibcode=2001Palai..16..482R |s2cid=130116586 }}</ref>

Several researchers support the existence of [[Paleocene dinosaurs|Paleocene non-avian dinosaurs]]. Evidence of this existence is based on the discovery of dinosaur remains in the [[Hell Creek Formation]] up to {{convert|1.3|m|ft|1|abbr=on}} above and 40,000&nbsp;years later than the K–Pg boundary.<ref name="Sloan">{{cite journal |author1=Sloan, R. E. |author2=Rigby, K. |author3=van&nbsp;Valen, L. M. |author4=Gabriel, Diane |s2cid=31638639 |year=1986 |title=Gradual dinosaur extinction and simultaneous ungulate radiation in the Hell Creek formation |journal=[[Science (journal)|Science]] |volume=232 |issue=4750 |pages=629–633 |doi=10.1126/science.232.4750.629 |pmid=17781415 |bibcode=1986Sci...232..629S }}</ref> Pollen samples recovered near a fossilized [[hadrosaur]] [[femur]] recovered in the [[Ojo Alamo Formation|Ojo Alamo Sandstone]] at the [[San Juan River (Colorado River tributary)|San Juan River]] in Colorado, indicate that the animal lived during the Cenozoic, approximately {{val|64.5|u=Ma}} (about 1&nbsp;million years after the K–Pg extinction event). If their existence past the K–Pg boundary can be confirmed, these hadrosaurids would be considered a [[Extinction debt|dead clade walking]].<ref name="Fassett">{{cite conference |title=Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone San Juan Basin, New Mexico and Colorado, USA |author1=Fassett, J. E. |author2=Lucas, S. G. |author3=Zielinski, R. A. |author4=Budahn, J. R. |year=2001 |conference=International Conference on Catastrophic Events and Mass Extinctions: Impacts and Beyond, 9–12 July 2000 |location=Vienna, Austria |volume=1053 |pages=45–46 |url=http://www.lpi.usra.edu/meetings/impact2000/pdf/3139.pdf |access-date=2007-05-18 |bibcode=2001caev.conf.3139F |archive-url=https://web.archive.org/web/20110605175701/http://www.lpi.usra.edu/meetings/impact2000/pdf/3139.pdf |archive-date=5 June 2011 |url-status=live}}</ref> The scientific consensus is that these fossils were eroded from their original locations and then re-buried in much later sediments (also known as [[Fossil#Derived, or reworked|reworked fossils]]).<ref name="Sullivan">{{cite journal |author=Sullivan, R. M. |year=2003 |title=No Paleocene dinosaurs in the San Juan Basin, New Mexico |url= http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm |journal=Geological Society of America Abstracts with Programs |volume=35 |issue=5 |page=15 |access-date=2007-07-02 |archive-url=https://web.archive.org/web/20110408155457/http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm |archive-date=2011-04-08}}</ref>

====Birds====
Most [[Paleontology|paleontologists]] regard birds as the only surviving dinosaurs (see [[Origin of birds]]). It is thought that all non-avian [[Theropoda|theropods]] became extinct, including then-flourishing groups such as [[enantiornithes|enantiornithines]] and [[hesperornithes|hesperornithiforms]].<ref>{{cite journal |author1=Hou, L. |author2=Martin, M. |author3=Zhou, Z. |author4=Feduccia, A. |year=1996 |title=Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China |journal=[[Science (journal)|Science]] |volume=274 |issue=5290 |pages=1164–1167 |bibcode=1996Sci...274.1164H |doi=10.1126/science.274.5290.1164 |pmid=8895459 |s2cid=30639866}}</ref> Several analyses of bird fossils show divergence of species prior to the K–Pg boundary, and that duck, chicken, and [[ratite]] bird relatives coexisted with non-avian dinosaurs.<ref>{{cite journal |author1=Clarke, J.A. |author2=Tambussi, C.P. |author3=Noriega, J.I. |author4=Erickson, G.M. |author5=Ketcham, R.A. |year=2005 |title=Definitive fossil evidence for the extant avian radiation in the Cretaceous |url=http://doc.rero.ch/record/15294/files/PAL_E2593.pdf |journal=[[Nature (journal)|Nature]] |volume=433 |issue=7023 |pages=305–308 |bibcode=2005Natur.433..305C |doi=10.1038/nature03150 |pmid=15662422 |s2cid=4354309 |hdl=11336/80763}}</ref> Large collections of bird fossils representing a range of different species provide definitive evidence for the persistence of archaic birds to within 300,000&nbsp;years of the K–Pg boundary. The absence of these birds in the Paleogene is evidence that a mass extinction of archaic birds took place there.<ref name="longrichetal2011" />

The most successful and dominant group of [[avialan]]s, [[enantiornithes]], were wiped out. Only a small fraction of ground and water-dwelling Cretaceous bird species survived the impact, giving rise to today's birds.<ref name="longrichetal2011" /><ref>{{cite web |date=20 September 2011 |title=Primitive birds shared dinosaurs' fate |publisher=Science Daily |url= https://www.sciencedaily.com/releases/2011/09/110919151315.htm |url-status=live |archive-url=https://web.archive.org/web/20110924053712/http://www.sciencedaily.com/releases/2011/09/110919151315.htm |archive-date=24 September 2011 |access-date=20 September 2011}}</ref> The only bird group known for certain to have survived the K–Pg boundary is the Aves.<ref name="longrichetal2011" /> Avians may have been able to survive the extinction as a result of their abilities to dive, swim, or seek shelter in water and marshlands. Many species of avians can build burrows, or nest in tree holes, or termite nests, all of which provided shelter from the environmental effects at the K–Pg boundary. Long-term survival past the boundary was assured as a result of filling ecological niches left empty by extinction of non-avian dinosaurs.<ref name="Robertson" /> Based on molecular sequencing and fossil dating, many species of birds (the [[Neoaves]] group in particular) appeared to radiate after the K–Pg boundary.<ref name="Feduccia, A. 1995" /><ref>{{cite journal |author1=Ericson, P. G. |author2=Anderson, C. L. |author3=Britton, T. |display-authors=etal |date=December 2006 |title=Diversification of Neoaves: integration of molecular sequence data and fossils |journal=[[Biology Letters]] |volume=2 |issue=4 |pages=543–7 |doi=10.1098/rsbl.2006.0523 |pmc=1834003 |pmid=17148284}}</ref> The open niche space and relative scarcity of predators following the K-Pg extinction allowed for adaptive radiation of various avian groups. [[Ratite]]s, for example, rapidly diversified in the early Paleogene and are believed to have convergently developed flightlessness at least three to six times, often fulfilling the niche space for large herbivores once occupied by non-avian dinosaurs.<ref name="Feduccia, A. 1995" /><ref>{{Cite journal |last1=Mitchell |first1=K.J. |last2=Llamas |first2=B. |last3=Soubrier |first3=J. |last4=Rawlence |first4=N. J. |last5=Worthy |first5=T. H. |last6=Wood |first6=J. |last7=Lee |first7=M. S. Y. |last8=Cooper |first8=A. |date=2014 |title=Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution |journal=[[Science (journal)|Science]] |volume=344 |issue=6186 |pages=989–900 |bibcode=2014Sci...344..898M |doi=10.1126/science.1251981 |pmid=24855267 |s2cid=206555952 |hdl-access=free |hdl=2328/35953}}</ref><ref>{{Cite journal |last1=Yonezawa |first1=Takahiro |last2=Segawa |first2=Takahiro |last3=Mori |first3=Hiroshi |last4=Campos |first4=Paula F. |last5=Hongoh |first5=Yuichi |last6=Endo |first6=Hideki |last7=Akiyoshi |first7=Ayumi |last8=Kohno |first8=Naoki |last9=Nishida |first9=Shin |last10=Wu |first10=Jiaqi |last11=Jin |first11=Haofei |date=2017 |title=Phylogenomics and Morphology of Extinct Paleognaths Reveal the Origin and Evolution of the Ratites |journal=[[Current Biology]] |volume=27 |issue=1 |pages=68–77 |pmid=27989673 |doi=10.1016/j.cub.2016.10.029 |doi-access=free}}</ref>

=== Mammals ===
Mammalian species began diversifying approximately 30&nbsp;million years prior to the K–Pg boundary. Diversification of mammals stalled across the boundary.<ref name="Bininda-Emonds">{{cite journal |author1=Bininda-Emonds, O. R. |author2=Cardillo M. |author3=Jones, K. E. |author4=MacPhee, R. D. |author5=Beck, R. M. |author6=Grenyer, R. |author7=Price, S. A. |author8=Vos, R. A. |author9=Gittleman, J. L. |author10=Purvis, A. |year=2007 |title=The delayed rise of present-day mammals |journal=[[Nature (journal)|Nature]] |volume=446 |issue=7135 |pages=507–512 |bibcode=2007Natur.446..507B |doi=10.1038/nature05634 |pmid=17392779 |s2cid=4314965}}</ref> All major Late Cretaceous mammalian lineages, including [[monotreme]]s (egg-laying mammals), [[multituberculata|multituberculates]], [[metatheria]]ns (which includes modern marsupials), [[eutheria]]ns (which includes modern placentals), [[Meridiolestida|meridiolestidans]],<ref>{{cite journal |author1=Gelfo, J. N. |author2=Pascual, R. |year=2001 |title=''Peligrotherium tropicalis'' (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation |journal=[[Geodiversitas]] |volume=23 |pages=369–379 |url=http://www.mnhn.fr/publication/geodiv/g01n3a4.pdf  |archive-url=https://web.archive.org/web/20120212193611/http://www.mnhn.fr/publication/geodiv/g01n3a4.pdf |archive-date=2012-02-12}}</ref> and [[gondwanatheria|gondwanatheres]]<ref>{{cite journal |author1=Goin, F. J. |author2=Reguero, M. A. |author3=Pascual, R. |author4=von Koenigswald, W. |author5=Woodburne, M. O. |author6=Case, J. A. |author7=Marenssi, S. A. |author8=Vieytes, C. |author9=Vizcaíno, S. F. |s2cid=129493664 |year=2006 |title=First gondwanatherian mammal from Antarctica |journal=Geological Society, London |series=Special Publications |volume=258 |issue=1 |pages=135–144 |doi=10.1144/GSL.SP.2006.258.01.10 |bibcode=2006GSLSP.258..135G}}</ref> survived the K–Pg extinction event, although they suffered losses. In particular, metatherians largely disappeared from North America, and the Asian [[deltatheroida]]ns became extinct (aside from the lineage leading to ''[[Gurbanodelta]]'').<ref name="classofmamm">{{cite book |author1=McKenna, M. C. |author2=Bell, S. K. |title=Classification of mammals: Above the species level |publisher=Columbia University Press |year=1997 |isbn=978-0-231-11012-9}}</ref><!--Only peradectids and herpetotheriids remained (and ''Esteslestes'', affinities unclear); stagodontids, pediomyoids and some other stuff became extinct. There are 17 Late Cretaceous (more have since been described) and 3 Paleocene North American metatherians in McKenna and Bell--> In the Hell Creek beds of North America, at least half of the ten known multituberculate species and all eleven metatherians species are not found above the boundary.<ref name="AF04"/> Multituberculates in Europe and North America survived relatively unscathed and quickly bounced back in the Paleocene, but Asian forms were devastated, never again to represent a significant component of mammalian fauna.<ref name="Wood 2010">{{cite thesis |last=Wood |first=D. Joseph |title=The Extinction of the Multituberculates Outside North America: a Global Approach to Testing the Competition Model |type=M.S. |year=2010 |publisher=The Ohio State University |url=https://etd.ohiolink.edu/!etd.send_file?accession=osu1275595604&disposition=inline |access-date=2015-04-03 |archive-url=https://web.archive.org/web/20150408104907/https://etd.ohiolink.edu/!etd.send_file?accession=osu1275595604&disposition=inline |archive-date=2015-04-08 |url-status=live}}</ref> A recent study indicates that metatherians suffered the heaviest losses at the K–Pg event, followed by multituberculates, while eutherians recovered the quickest.<ref>{{cite journal |first1=Mathias M. |last1=Pires |first2=Brian D. |last2=Rankin |first3=Daniele |last3=Silvestro |first4=Tiago B. |last4=Quental |year=2018 |title=Diversification dynamics of mammalian clades during the K–Pg mass extinction |journal=[[Biology Letters]] |volume=14 |issue=9 |page=20180458 |pmc=6170748 |pmid=30258031 |doi=10.1098/rsbl.2018.0458}}</ref> K–Pg boundary mammalian species were generally small, comparable in size to [[rat]]s; this small size would have helped them find shelter in protected environments. It is postulated that some early monotremes, marsupials, and placentals were semiaquatic or burrowing, as there are multiple mammalian lineages with such habits today. Any burrowing or semiaquatic mammal would have had additional protection from K–Pg boundary environmental stresses.<ref name="Robertson" />

After the K–Pg extinction, mammals evolved to fill the niches left vacant by the dinosaurs.<ref>{{Cite journal |last1=Springer |first1=Mark S. |last2=Foley |first2=Nicole M. |last3=Brady |first3=Peggy L. |last4=Gatesy |first4=John |last5=Murphy |first5=William J. |date=29 November 2019 |title=Evolutionary Models for the Diversification of Placental Mammals Across the KPg Boundary |journal=[[Frontiers in Genetics]] |volume=10 |page=1241 |doi=10.3389/fgene.2019.01241 |issn=1664-8021 |pmc=6896846 |pmid=31850081 |doi-access=free }}</ref><ref>{{Cite journal |last1=Shupinski |first1=Alex B. |last2=Wagner |first2=Peter J. |last3=Smith |first3=Felisa A. |last4=Lyons |first4=S. Kathleen |date=3 July 2024 |title=Unique functional diversity during early Cenozoic mammal radiation of North America |journal=[[Proceedings of the Royal Society B: Biological Sciences]] |language=en |volume=291 |issue=2026 |doi=10.1098/rspb.2024.0778 |issn=1471-2954 |pmc=11286128 |pmid=38955231 |pmc-embargo-date=July 3, 2025 }}</ref> Some research indicates that mammals did not explosively diversify across the K–Pg boundary, despite the ecological niches made available by the extinction of dinosaurs.<ref name="Springer">{{cite journal |title=Placental mammal diversification and the Cretaceous–Tertiary boundary |year=2003 |author1=Springer, M. S. |author2=Murphy, W. J. |author3=Eizirik, E. |author4=O'Brien, S. J. |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=100 |issue=3 |pages=1056–1061 |doi=10.1073/pnas.0334222100 |pmid=12552136 |pmc=298725 |bibcode=2003PNAS..100.1056S |doi-access=free}}</ref> Several mammalian orders have been interpreted as diversifying immediately after the K–Pg boundary, including Chiroptera ([[bat]]s) and Cetartiodactyla (a diverse group that today includes [[cetaceans|whales and dolphins]] and [[even-toed ungulate]]s),<ref name="Springer"/> although recent research concludes that only [[marsupial]] orders diversified soon after the K–Pg boundary.<ref name="Bininda-Emonds"/> However, morphological diversification rates among eutherians after the extinction event were thrice those of before it.<ref>{{Cite journal |last1=Halliday |first1=Thomas John Dixon |last2=Upchurch |first2=Paul |last3=Goswami |first3=Anjali |date=29 June 2016 |title=Eutherians experienced elevated evolutionary rates in the immediate aftermath of the Cretaceous–Palaeogene mass extinction |journal=[[Proceedings of the Royal Society B: Biological Sciences]] |language=en |volume=283 |issue=1833 |pages=20153026 |doi=10.1098/rspb.2015.3026 |issn=0962-8452 |pmc=4936024 |pmid=27358361 }}</ref> Also significant, within the mammalian genera, new species were approximately 9.1% larger after the K–Pg boundary.<ref>{{cite journal |author=Alroy, J. |date=May 1998 |title=Cope's rule and the dynamics of body mass evolution in North American fossil mammals |url=http://doc.rero.ch/record/20309/files/PAL_E4068.pdf |journal=[[Science (journal)|Science]] |volume=280 |issue=5364 |pages=731–4 |bibcode=1998Sci...280..731A |doi=10.1126/science.280.5364.731 |pmid=9563948}}</ref> After about 700,000 years, some mammals had reached 50 kilos (110 pounds), a 100-fold increase over the weight of those which survived the extinction.<ref>[https://www.science.org/content/article/how-life-blossomed-after-dinosaurs-died How life blossomed after the dinosaurs died | Science | AAAS]</ref> It is thought that body sizes of placental mammalian survivors [[Evolutionary radiation#Examples|evolutionarily]] increased first, allowing them to fill niches after the extinctions, with [[brain size]]s increasing <!--only (mostly)-->later in the [[Eocene]].<ref>{{cite news |date=31 March 2022 |title=Mammals' bodies outpaced their brains right after the dinosaurs died |work=[[Science News]] |url=https://www.sciencenews.org/article/mammal-big-bodies-small-brains-dinosaur-extinction-fossils |access-date=14 May 2022}}</ref><ref>{{cite journal |last1=Bertrand |first1=Ornella C. |last2=Shelley |first2=Sarah L. |last3=Williamson |first3=Thomas E. |last4=Wible |first4=John R. |last5=Chester |first5=Stephen G. B. |last6=Flynn |first6=John J. |last7=Holbrook |first7=Luke T. |last8=Lyson |first8=Tyler R. |last9=Meng |first9=Jin |last10=Miller |first10=Ian M. |last11=Püschel |first11=Hans P. |last12=Smith |first12=Thierry |last13=Spaulding |first13=Michelle |last14=Tseng |first14=Z. Jack |last15=Brusatte |first15=Stephen L. |date=April 2022 |title=Brawn before brains in placental mammals after the end-Cretaceous extinction |journal=[[Science (journal)|Science]] |language=en |volume=376 |issue=6588 |pages=80–85 |bibcode=2022Sci...376...80B |doi=10.1126/science.abl5584 |pmid=35357913 |s2cid=247853831 |hdl=20.500.11820/d7fb8c6e-886e-4c1d-9977-0cd6406fda20 |hdl-access=free |issn=0036-8075|url=https://www.pure.ed.ac.uk/ws/files/251642227/Bertrand_et_al._Science.pdf }}</ref>

===Terrestrial plants===
Plant fossils illustrate the reduction in plant species across the K–Pg boundary. There is overwhelming evidence of global disruption of plant communities at the K–Pg boundary.<ref name="Vajdaetal">{{cite journal |last1=Vajda |first1=Vivi |last2=Raine |first2=J. Ian |last3=Hollis |first3=Christopher J. |year=2001 |title=Indication of global deforestation at the Cretaceous–Tertiary boundary by New Zealand fern spike |journal=[[Science (journal)|Science]] |volume=294 |issue=5547 |pages=1700–1702 |bibcode=2001Sci...294.1700V |doi=10.1126/science.1064706 |pmid=11721051 |s2cid=40364945}}</ref><ref name="autogenerated347" /> Extinctions are seen both in studies of fossil pollen, and fossil leaves.<ref name="Nichols, D. J 2008" /> In North America, the data suggests massive devastation and mass extinction of plants at the K–Pg boundary sections, although there were substantial megafloral changes before the boundary.<ref>{{cite book |author1=Johnson, K.R. |title=Global Catastrophes in Earth History: An interdisciplinary conference on impacts, volcanism, and mass mortality |author2=Hickey, L.J. |publisher=Geological Society of America |year=1991 |isbn=978-0-8137-2247-4 |editor1=Sharpton, V.I. |article=Megafloral change across the Cretaceous Tertiary boundary in the northern Great Plains and Rocky Mountains |editor2=Ward, P.D.}}</ref> In North America, approximately 57% of plant species became extinct. In high southern hemisphere latitudes, such as New Zealand and Antarctica, the mass die-off of flora caused no significant turnover in species, but dramatic and short-term changes in the relative abundance of plant groups.<ref name="Labandieraetal" /><ref>{{cite book |last1=Askin |first1=R.A. |title=Cretaceous–Tertiary Mass Extinctions: Biotic and Environmental Changes |last2=Jacobson |first2=S.R. |publisher=W W Norton |year=1996 |isbn=978-0-393-96657-2 |editor1=Keller, G. |article=Palynological change across the Cretaceous–Tertiary boundary on Seymour Island, Antarctica: environmental and depositional factors |editor2=MacLeod, N.}}</ref> European flora was also less affected, most likely due to its distance from the site of the Chicxulub impact.<ref>{{Cite journal |last1=Wappler |first1=Torsten |last2=Currano |first2=Ellen D. |last3=Wilf |first3=Peter |last4=Rust |first4=Jes |last5=Labandeira |first5=Conrad C. |date=22 December 2009 |title=No post-Cretaceous ecosystem depression in European forests? Rich insect-feeding damage on diverse middle Palaeocene plants, Menat, France |journal=[[Proceedings of the Royal Society B: Biological Sciences]] |language=en |volume=276 |issue=1677 |pages=4271–4277 |doi=10.1098/rspb.2009.1255 |issn=0962-8452 |pmc=2817104 |pmid=19776074}}</ref> In northern Alaska and the Anadyr-Koryak region of Russia, the flora was minimally impacted.<ref>{{Cite journal |last1=Herman |first1=A. B. |last2=Akhmetiev |first2=M. A. |last3=Kodrul |first3=T. M. |last4=Moiseeva |first4=M. G. |last5=Iakovleva |first5=A. I. |date=24 February 2009 |title=Flora development in Northeastern Asia and Northern Alaska during the Cretaceous-Paleogene transitional epoch |journal=[[Stratigraphy and Geological Correlation]] |language=en |volume=17 |issue=1 |pages=79–97 |doi=10.1134/S0869593809010079 |issn=0869-5938}}</ref><ref>{{Cite journal |last=Herman |first=A. B. |date=10 December 2013 |title=Albian-Paleocene flora of the north pacific: Systematic composition, palaeofloristics and phytostratigraphy |journal=[[Stratigraphy and Geological Correlation]] |language=en |volume=21 |issue=7 |pages=689–747 |doi=10.1134/S0869593813070034 |issn=0869-5938}}</ref> Another line of evidence of a major floral extinction is that the divergence rate of subviral pathogens of angiosperms sharply decreased, which indicates an enormous reduction in the number of flowering plants.<ref>{{cite journal |last1=Bajdek |first1=Piotr |date=10 May 2019 |title=Divergence rates of subviral pathogens of angiosperms abruptly decreased at the Cretaceous-Paleogene boundary |url=https://rethinkingecology.pensoft.net/article/33014/ |journal=Rethinking Ecology |volume=4 |pages=89–101 |doi=10.3897/rethinkingecology.4.33014 |s2cid=196664424 |access-date=23 March 2023 |doi-access=free}}</ref> However, phylogenetic evidence shows no mass angiosperm extinction.<ref>{{Cite journal |last1=Thompson |first1=Jamie B. |last2=Ramírez-Barahona |first2=Santiago |date=September 2023 |title=No phylogenetic evidence for angiosperm mass extinction at the Cretaceous–Palaeogene (K-Pg) boundary |journal=Biology Letters |language=en |volume=19 |issue=9 |doi=10.1098/rsbl.2023.0314 |issn=1744-957X |pmc=10498348 |pmid=37700701}}</ref>

Due to the wholesale destruction of plants at the K–Pg boundary, there was a proliferation of [[Saprotrophic nutrition|saprotrophic]] organisms, such as [[fungus|fungi]], that do not require photosynthesis and use nutrients from decaying vegetation. The dominance of fungal species lasted only a few years while the atmosphere cleared and plenty of organic matter to feed on was present. Once the atmosphere cleared photosynthetic organisms returned – initially ferns and other ground-level plants.<ref name="Vajda-McLoughlin-2004">{{cite journal |last1=Vajda |first1=Vivi |last2=McLoughlin |first2=Stephen |date=5 March 2004 |title=Fungal Proliferation at the Cretaceous-Tertiary Boundary |url=http://nrm.diva-portal.org/smash/get/diva2:719366/FULLTEXT01 |journal=[[Science (journal)|Science]] |volume=303 |issue=5663 |page=1489 |doi=10.1126/science.1093807 |pmid=15001770 |s2cid=44720346}}</ref>

In some regions, the Paleocene recovery of plants began with recolonizations by fern species, represented as a [[fern spike]] in the geologic record; this same pattern of fern recolonization was observed after the [[1980 eruption of Mount St. Helens|1980 Mount St.&nbsp;Helens eruption]].<ref name="SchultzDhondt">{{cite journal |last1=Schultz |first1=P. |last2=d'Hondt |first2=S. |year=1996 |title=Cretaceous–Tertiary (Chicxulub) impact angle and its consequences |journal=[[Geology (journal)|Geology]] |volume=24 |issue=11 |pages=963–967 |bibcode=1996Geo....24..963S |doi=10.1130/0091-7613(1996)024<0963:CTCIAA>2.3.CO;2}}</ref>
Just two species of fern appear to have dominated the landscape for centuries after the event.<ref>{{Cite journal |last1=Field |first1=Daniel J. |last2=Bercovici |first2=Antoine |last3=Berv |first3=Jacob S. |last4=Dunn |first4=Regan |last5=Fastovsky |first5=David E. |last6=Lyson |first6=Tyler R. |last7=Vajda |first7=Vivi |last8=Gauthier |first8=Jacques A. |display-authors=6 |date=24 May 2018 |title=Early evolution of modern birds structured by global forest collapse at the end-Cretaceous mass extinction |journal=[[Current Biology]] |volume=28 |issue=11 |pages=1825–1831.e2 |doi=10.1016/j.cub.2018.04.062 |pmid=29804807 |s2cid=44075214 |doi-access=free|bibcode=2018CBio...28E1825F }}</ref> In the sediments below the K–Pg boundary the dominant plant remains are [[angiosperm]] pollen grains, but the boundary layer contains little pollen and is dominated by fern spores.<ref name="USGS">{{cite web |year=2004 |title=Online guide to the continental Cretaceous–Tertiary boundary in the Raton basin, Colorado and New Mexico |url=http://esp.cr.usgs.gov/info/kt/stop2b.html |archive-url=https://web.archive.org/web/20060925223706/http://esp.cr.usgs.gov/info/kt/stop2b.html |archive-date=2006-09-25 |access-date=2007-07-08 |publisher=U.S. Geological Survey}}</ref> More usual pollen levels gradually resume above the boundary layer. This is reminiscent of areas blighted by modern volcanic eruptions, where the recovery is led by ferns, which are later replaced by larger angiosperm plants.<ref>{{cite book |last1=Smathers |first1=G.A. |url=http://www.nps.gov/history/history/online_books/science/5/contents.htm |title=Invasion and Recovery of Vegetation after a Volcanic Eruption in Hawaii |last2=Mueller-Dombois |first2=D. |publisher=United States National Park Service |year=1974 |series=Scientific Monograph |volume=5 |access-date=2007-07-09 |archive-url=https://web.archive.org/web/20140403124910/http://www.nps.gov/history/history/online_books/science/5/contents.htm |archive-date=2014-04-03 |url-status=live}}</ref> In North American terrestrial sequences, the extinction event is best represented by the marked discrepancy between the rich and relatively abundant late-Maastrichtian [[palynomorph|pollen]] record and the post-boundary fern spike.<ref name="Vajdaetal" />

[[Polyploidy]] appears to have enhanced the ability of flowering plants to survive the extinction, probably because the additional copies of the genome such plants possessed allowed them to more readily adapt to the rapidly changing environmental conditions that followed the impact.<ref name="Fawcett2009">{{cite journal |last1=Fawcett |first1=Jeffrey A. |last2=Maere |first2=Steven |last3=Van de Peer |first3=Yves |date=April 2009 |title=Plants with double genomes might have had a better chance to survive the Cretaceous-Tertiary extinction event |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=106 |issue=14 |pages=5737–5742 |bibcode=2009PNAS..106.5737F |doi=10.1073/pnas.0900906106 |pmc=2667025 |pmid=19325131 |doi-access=free}}</ref>

Beyond extinction impacts, the event also caused more general changes of flora such as giving rise to [[Neotropical realm|neotropical]] [[rainforest]] [[biome]]s like the [[Amazonia]], replacing species composition and structure of local forests [[Paleocene|during ~6&nbsp;million years of recovery]] to former levels of plant [[biodiversity|diversity]].<ref>{{cite news |date=2 April 2021 |title=Dinosaur-killing asteroid strike gave rise to Amazon rainforest |url=https://www.bbc.com/news/science-environment-56617409 |access-date=9 May 2021 |website=[[BBC News]]}}</ref><ref>{{cite journal |last1=Carvalho |first1=Mónica R. |last2=Jaramillo |first2=Carlos |last3=Parra |first3=Felipe de la |last4=Caballero-Rodríguez |first4=Dayenari |last5=Herrera |first5=Fabiany |last6=Wing |first6=Scott |last7=Turner |first7=Benjamin L. |last8=D'Apolito |first8=Carlos |last9=Romero-Báez |first9=Millerlandy |last10=Narváez |first10=Paula |last11=Martínez |first11=Camila |last12=Gutierrez |first12=Mauricio |last13=Labandeira |first13=Conrad |last14=Bayona |first14=German |last15=Rueda |first15=Milton |last16=Paez-Reyes |first16=Manuel |last17=Cárdenas |first17=Dairon |last18=Duque |first18=Álvaro |last19=Crowley |first19=James L. |last20=Santos |first20=Carlos |last21=Silvestro |first21=Daniele |display-authors=3 |date=2 April 2021 |title=Extinction at the end-Cretaceous and the origin of modern Neotropical rainforests |journal=[[Science (journal)|Science]] |language=en |volume=372 |issue=6537 |pages=63–68 |bibcode=2021Sci...372...63C |doi=10.1126/science.abf1969 |doi-access=free |issn=0036-8075 |pmid=33795451 |s2cid=232484243 |url=https://www.researchgate.net/publication/350569900 |access-date=9 May 2021}}</ref>

===Fungi===
While it appears that many fungi were wiped out at the K-Pg boundary, there is some evidence that some fungal species thrived in the years after the extinction event. Microfossils from that period indicate a great increase in fungal spores, long before the resumption of plentiful fern spores in the recovery after the impact. Monoporisporites and [[hypha]] are almost exclusive microfossils for a short span during and after the iridium boundary. These [[Saprotrophic nutrition|saprophytes]] would not need sunlight, allowing them to survive during a period when the atmosphere was likely clogged with dust and sulfur aerosols.<ref name="Vajda-McLoughlin-2004" />

The proliferation of fungi has occurred after several extinction events, including the [[Permian–Triassic extinction event]], the largest known mass extinction in Earth's history, with up to 96% of all species suffering extinction.<ref>{{cite journal |last1=Visscher |first1=H. |last2=Brinkhuis |first2=H. |last3=Dilcher |first3=D. L. |last4=Elsik |first4=W. C. |last5=Eshet |first5=Y. |last6=Looy |first6=C. V. |last7=Rampino |first7=M. R. |last8=Traverse |first8=A. |date=5 March 1996 |title=The terminal Paleozoic fungal event: evidence of terrestrial ecosystem destabilization and collapse. |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=93 |issue=5 |pages=2155–2158 |bibcode=1996PNAS...93.2155V |doi=10.1073/pnas.93.5.2155 |pmc=39926 |pmid=11607638 |doi-access=free}}</ref>

== Dating ==
[[File: Hell Creek.jpg|thumb|alt=aerial view of the canyon with mesas and creek in background|[[Hell Creek Formation]]]]
A 1991 study of fossil leaves [[Chronological dating|dated]] the extinction-associated freezing to early June.<ref>{{cite journal| author=Jack Wolfe| title=Palaeobotanical evidence for a June 'impact winter' at the Cretaceous/Tertiary boundary| journal=Nature| url=https://www.nature.com/articles/352420a0.epdf?sharing_token=SZ2zIDwp4nwPzqW21MBRWdRgN0jAjWel9jnR3ZoTv0M7VLIKoE6x4ag0Nr_AUthe7MxQ_v5tDeeuXolxlXkVi1rOJ-QBzJ-jws0_6AgoDTZ1jGwfolUTVzyctXnuY6AmMFuTIS3OvXWg_NJMTFUMFjCyE1WglpNX1Vg16yxkSt4Mmjas8D9WIxl3VRQ66tWvEI3uj-BYCYv86RvbDAb7-Q%3D%3D| year =1991| volume=352| issue=6334| page=420| doi=10.1038/352420a0| bibcode=1991Natur.352..420W| s2cid=4242454}}</ref> A later study shifted the dating to spring season, based on the [[osteological]] evidence and [[stable isotope]] records of well-preserved bones of [[acipenseriform]] fishes. The study noted that "the [[Paleobotany|palaeobotanical]] identities, [[taphonomic]] inferences and [[stratigraphic]] assumptions" for the June dating have since all been refuted.<ref>{{cite journal | title =The Mesozoic terminated in boreal spring| journal =Nature| date =23 February 2022| doi =10.1038/s41586-022-04446-1| last1 =During| first1 =Melanie A. D.| last2 =Smit| first2 =Jan| last3 =Voeten| first3 =Dennis F. A. E.| last4 =Berruyer| first4 =Camille| last5 =Tafforeau| first5 =Paul| last6 =Sanchez| first6 =Sophie| last7 =Stein| first7 =Koen H. W.| last8 =Verdegaal-Warmerdam| first8 =Suzan J. A.| last9 =Van Der Lubbe| first9 =Jeroen H. J. L.| volume =603| issue =7899| pages =91–94| pmid =35197634| pmc =8891016| bibcode =2022Natur.603...91D}}</ref> Another modern study opted for the spring–summer range.<ref>{{cite journal | title =Seasonal calibration of the end-cretaceous Chicxulub impact event| journal =Nature| date =8 December 2021| doi =10.1038/s41598-021-03232-9| last1 =Depalma| first1 =Robert A.| last2 =Oleinik| first2 =Anton A.| last3 =Gurche| first3 =Loren P.| last4 =Burnham| first4 =David A.| last5 =Klingler| first5 =Jeremy J.| last6 =McKinney| first6 =Curtis J.| last7 =Cichocki| first7 =Frederick P.| last8 =Larson| first8 =Peter L.| last9 =Egerton| first9 =Victoria M.| last10 =Wogelius| first10 =Roy A.| last11 =Edwards| first11 =Nicholas P.| last12 =Bergmann| first12 =Uwe| last13 =Manning| first13 =Phillip L.| volume =11| issue =1| page =23704| pmid =34880389| pmc =8655067| bibcode =2021NatSR..1123704D}}</ref> A study of fossilized fish bones found at [[Tanis (fossil site)|Tanis]] in [[North Dakota]] suggests that the Cretaceous-Paleogene mass extinction happened during the Northern Hemisphere spring.<ref>{{Cite journal |last1=During |first1=Melanie A. D. |last2=Smit |first2=Jan |last3=Voeten |first3=Dennis F. A. E. |last4=Berruyer |first4=Camille |last5=Tafforeau |first5=Paul |last6=Sanchez |first6=Sophie |last7=Stein |first7=Koen H. W. |last8=Verdegaal-Warmerdam |first8=Suzan J. A. |last9=van der Lubbe |first9=Jeroen H. J. L. |display-authors=3 |date=February 23, 2022 |title=The Mesozoic terminated in boreal spring |journal=Nature |volume=603 |issue=7899 |pages=91–94 |bibcode=2022Natur.603...91D |doi=10.1038/s41586-022-04446-1 |pmc=8891016 |pmid=35197634}}</ref><ref>{{cite web |date=2022-02-23 |title=Springtime was the season the dinosaurs died, ancient fish fossils suggest |url=https://www.science.org/content/article/springtime-was-season-dinosaurs-died-ancient-fish-fossils-suggest |access-date=2022-02-24 |work=[[Science (journal)|Science]]}}</ref><ref>{{cite journal |last1=Barras |first1=Colin |date=2022-02-23 |title=Fossil fish reveal timing of asteroid that killed the dinosaurs |journal=[[Nature (journal)|Nature]] |volume=603 |issue=7899 |page=17 |bibcode=2022Natur.603...17B |doi=10.1038/d41586-022-00511-x |pmid=35197589 |s2cid=247083600 |doi-access=free}}</ref><ref name="AT-20220223">{{cite news |last=Ouellette |first=Jennifer |author-link=Jennifer Ouellette |date=23 February 2022 |title=An asteroid killed dinosaurs in spring—which might explain why mammals survived – New study sheds light on why species extinction was so selective after the K-Pg impact |work=[[Ars Technica]] |url=https://arstechnica.com/science/2022/02/fish-fossils-show-asteroid-that-wiped-out-the-dinosaurs-struck-in-the-spring/ |access-date=26 February 2022}}</ref>

== Duration ==
The extinction's rapidity is a controversial issue because some researchers think the extinction was the result of a sudden event, while others argue that it took place over a long period. The exact length of time is difficult to determine because of the [[Signor–Lipps effect]], where the fossil record is so incomplete that most extinct [[species]] probably died out long after the most recent fossil that has been found.<ref>{{cite book |title=Geological implications of impacts of large asteroids and comets on the Earth |publisher=Geological Society of America |year=1982 |contribution=Sampling bias, gradual extinction patterns, and catastrophes in the fossil record |id=Special Publication 190 |location=Boulder, CO |pages=291–296 |oclc=4434434112 |last2=Lipps |first2=Jere H. |last1=Signor |first1=Philip W. III |editor1-first=L.T. |editor1-last=Silver |editor2-first=Peter H.|editor2-last=Schultz|editor2-link=Peter H. Schultz|url=https://books.google.com/books?id=efz87W88HawC&pg=291 |isbn=978-0-8137-2190-3 |access-date=October 25, 2015}}</ref> Scientists have also found very few continuous beds of fossil-bearing rock that cover a time range from several million years before the K–Pg extinction to several million years after it.<ref name="MacLeod"/>

The sedimentation rate and thickness of K–Pg clay from three sites suggest rapid extinction, perhaps over a period of less than 10,000 years.<ref name=":1">{{cite journal |title=A Short Duration of the Cretaceous-Tertiary Boundary Event: Evidence from Extraterrestrial Helium-3 |last1=Mukhopadhyay |first1=Sujoy |date=2001 |journal=[[Science (journal)|Science]] |doi=10.1126/science.291.5510.1952 |pmid=11239153 |volume=291 |issue=5510 |pages=1952–1955 |bibcode=2001Sci...291.1952M |url=https://authors.library.caltech.edu/36545/7/Mukhopad3.sup.pdf }}</ref> At one site in the [[Denver Basin]] of [[Colorado]], after the K–Pg boundary layer was deposited, the [[fern spike]] lasted approximately 1,000 years, and no more than 71,000 years; at the same location, the earliest appearance of [[Cenozoic]] mammals occurred after approximately 185,000 years, and no more than 570,000 years, "indicating rapid rates of biotic extinction and initial recovery in the Denver Basin during this event."<ref>{{cite journal|last1=Clyde |first1=William C. |last2=Ramezani |first2=Jahandar |last3=Johnson |first3=Kirk R. |last4=Bowring |first4=Samuel A. |last5=Jones |first5=Matthew M. |title=Direct high-precision U–Pb geochronology of the end-Cretaceous extinction and calibration of Paleocene astronomical timescales |date=15 October 2016 |journal=[[Earth and Planetary Science Letters]] |volume=452 |pages=272–280 |doi=10.1016/j.epsl.2016.07.041 |bibcode=2016E&PSL.452..272C |doi-access=free}}</ref> Analysis of the carbon cycle disruptions caused by the impact constrains them to an interval of just 5,000 years.<ref>{{Cite journal |last1=Renne |first1=Paul R. |last2=Deino |first2=Alan L. |last3=Hilgen |first3=Frederik J. |last4=Kuiper |first4=Klaudia F. |last5=Mark |first5=Darren F. |last6=Mitchell |first6=William S. |last7=Morgan |first7=Leah E. |last8=Mundil |first8=Roland |last9=Smit |first9=Jan |date=8 February 2013 |title=Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary |journal=[[Science (journal)|Science]] |language=en |volume=339 |issue=6120 |pages=684–687 |doi=10.1126/science.1230492 |pmid=23393261 |bibcode=2013Sci...339..684R |issn=0036-8075}}</ref> Models presented at the annual meeting of the [[American Geophysical Union]] demonstrated that the period of global darkness following the [[Chicxulub impact]] would have persisted in the [[Hell Creek Formation]] nearly 2 years.<ref name=":2">{{Cite web |last=Weisberger |first=Mindy |date=2021-12-22 |title=Darkness caused by dino-killing asteroid snuffed out life on Earth in 9 months |url=https://www.livescience.com/cretaceous-extinction-darkness |access-date=2022-11-17 |website=livescience.com}}</ref>

== Causes ==

=== Chicxulub impact ===
{{Main|Cretaceous–Paleogene boundary|Alvarez hypothesis|Chicxulub crater}}

==== Evidence for impact ====
[[File:LWA with Walt.JPG|thumb|upright|[[Luis Walter Alvarez|Luis]], left, and his son [[Walter Alvarez]], right, at the [[Cretaceous–Paleogene boundary|K-T boundary]] in [[Gubbio]], Italy, 1981]]
[[File:LateCretaceousMap.jpg|thumb|upright=1.35|left|Late Cretaceous global map ([[Turonian]])]]
In 1980, a team of researchers consisting of [[Nobel Prize]]-winning physicist [[Luis Walter Alvarez|Luis Alvarez]], his son, geologist [[Walter Alvarez]], and chemists [[Frank Asaro]] and [[Helen Michel]] discovered that [[Sedimentary rock|sedimentary]] layers found all over the world at the Cretaceous–Paleogene boundary contain a [[concentration]] of [[iridium]] many times greater than normal (30, 160, and 20 times in three sections originally studied). Iridium is extremely rare in [[crust (geology)|Earth's crust]] because it is a [[Goldschmidt classification#Siderophile elements|siderophile element]] which mostly sank along with [[iron]] into [[Structure of the Earth#Core|Earth's core]] during [[planetary differentiation]].<ref name="Alvarez" /> Instead, iridium is more common in [[comet]]s and [[asteroid]]s.<ref name="Schulte10" /> Because of this, the Alvarez team suggested that an asteroid struck the Earth at the time of the K–Pg boundary.<ref name="Alvarez">{{cite journal |title=Extraterrestrial cause for the Cretaceous–Tertiary extinction |author1=Alvarez, Luis W. |author2=Alvarez, Walter |author3=Asaro, F. |author4=Michel, H. V. |s2cid=16017767 |year=1980 |journal=[[Science (journal)|Science]] |volume=208 |issue=4448 |pages=1095–1108 |doi=10.1126/science.208.4448.1095 |pmid=17783054 |bibcode=1980Sci...208.1095A |url=https://pdfs.semanticscholar.org/f23d/f624d2e7d945277a4c06d6d66008eb0f4242.pdf |archive-url=https://web.archive.org/web/20190824192051/https://pdfs.semanticscholar.org/f23d/f624d2e7d945277a4c06d6d66008eb0f4242.pdf  |archive-date=2019-08-24 }}</ref> There were earlier speculations on the possibility of an [[impact event]],<ref>{{cite journal |author=de Laubenfels, M. W. |title=Dinosaur extinction: One more hypothesis |journal=[[Journal of Paleontology]] |pages=207–218 |year=1956 |volume=30 |issue=1 |jstor=1300393}}</ref> but this was the first hard evidence,<ref name="Alvarez" /> and since then, studies have continued to demonstrate elevated iridium levels in association with the K-Pg boundary.<ref name=":5" /><ref name=":4" /><ref name=":3" /> This hypothesis was viewed as radical when first proposed, but additional evidence soon emerged. The boundary clay was found to be full of minute [[spherule]]s of rock, crystallized from droplets of molten rock formed by the impact.<ref>{{cite journal |author1=Smit, J. |author2=Klaver, J. |year=1981 |title=Sanidine spherules at the Cretaceous-Tertiary boundary indicate a large impact event |journal=[[Nature (journal)|Nature]] |volume=292 |issue=5818 |pages=47–49 |bibcode=1981Natur.292...47S |doi=10.1038/292047a0 |s2cid=4331801}}</ref><ref>{{Cite journal |last1=Olsson |first1=Richard K. |last2=Miller |first2=Kenneth G. |last3=Browning |first3=James V. |last4=Habib |first4=Daniel |last5=Sugarman |first5=Peter J. |date=1 August 1997 |title=Ejecta layer at the Cretaceous-Tertiary boundary, Bass River, New Jersey (Ocean Drilling Program Leg 174AX) |journal=[[Geology (journal)|Geology]] |language=en |volume=25 |issue=8 |pages=759 |doi=10.1130/0091-7613(1997)025<0759:ELATCT>2.3.CO;2 |issn=0091-7613}}</ref> [[Shocked quartz]]<ref group="lower-alpha">Shocked minerals have their internal structure deformed, and are created by intense pressures as in nuclear blasts and meteorite impacts.</ref> and other minerals were also identified in the K–Pg boundary.<ref>{{cite journal |author1=Bohor, B. F. |author2=Foord, E. E. |author3=Modreski, P. J. |author4=Triplehorn, D. M. |year=1984 |title=Mineralogic evidence for an impact event at the Cretaceous-Tertiary boundary |journal=[[Science (journal)|Science]] |volume=224 |issue=4651 |pages=867–9 |bibcode=1984Sci...224..867B |doi=10.1126/science.224.4651.867 |pmid=17743194 |s2cid=25887801}}</ref><ref>{{cite journal |author1=Bohor, B. F. |author2=Modreski, P. J. |author3=Foord, E. E. |year=1987 |title=Shocked quartz in the Cretaceous-Tertiary boundary clays: Evidence for a global distribution |url=https://zenodo.org/record/1230978 |journal=[[Science (journal)|Science]] |volume=236 |issue=4802 |pages=705–709 |bibcode=1987Sci...236..705B |doi=10.1126/science.236.4802.705 |pmid=17748309 |s2cid=31383614}}</ref> The identification of giant [[Tsunami deposit|tsunami beds]] along the Gulf Coast and the Caribbean provided more evidence,<ref>{{cite journal |author1=Bourgeois, J. |author2=Hansen, T. A. |author3=Wiberg, P. A. |author4=Kauffman, E. G. |year=1988 |title=A tsunami deposit at the Cretaceous-Tertiary boundary in Texas |journal=[[Science (journal)|Science]] |volume=241 |issue=4865 |pages=567–570 |bibcode=1988Sci...241..567B |doi=10.1126/science.241.4865.567 |pmid=17774578 |s2cid=7447635}}</ref> and suggested that the impact might have occurred nearby, as did the discovery that the K–Pg boundary became thicker in the southern United States, with meter-thick beds of debris occurring in northern New Mexico.<ref name="Nichols, D. J 2008" /> A K-Pg boundary "cocktail" of microfossils, lithic fragments, and impact-derived material deposited by gigantic sediment gravity flows was discovered in the Caribbean that served to demarcate the impact.<ref>{{Cite journal |last1=Bralower |first1=Timothy J. |last2=Paull |first2=Charles K. |last3=Mark Leckie |first3=R. |date=1 April 1998 |title=The Cretaceous-Tertiary boundary cocktail: Chicxulub impact triggers margin collapse and extensive sediment gravity flows |journal=[[Geology (journal)|Geology]] |language=en |volume=26 |issue=4 |pages=331 |doi=10.1130/0091-7613(1998)026<0331:TCTBCC>2.3.CO;2 |issn=0091-7613}}</ref> Further research identified the giant [[Chicxulub crater]], buried under [[Chicxulub Pueblo|Chicxulub]] on the coast of [[Yucatán Peninsula|Yucatán]], as the source of the K–Pg boundary clay. Identified in 1990<ref name="Hildebrand, A. R. 1991" /> based on work by geophysicist Glen Penfield in 1978, the crater is oval, with an average diameter of roughly {{convert|180|km|abbr=on}}, about the size calculated by the Alvarez team.<ref>{{cite journal |author1=Pope, K. O. |author2=Ocampo, A. C. |author3=Kinsland, G. L. |author4=Smith, R. |year=1996 |title=Surface expression of the Chicxulub crater |journal=[[Geology (journal)|Geology]] |volume=24 |issue=6 |pages=527–530 |bibcode=1996Geo....24..527P |doi=10.1130/0091-7613(1996)024<0527:SEOTCC>2.3.CO;2 |pmid=11539331}}</ref><ref>{{Cite journal |last1=Stöffler |first1=Dieter |last2=Artemieva |first2=Natalya A. |last3=Ivanov |first3=Boris A. |last4=Hecht |first4=Lutz |last5=Kenkmann |first5=Thomas |last6=Schmitt |first6=Ralf Thomas |last7=Tagle |first7=Roald Alberto |last8=Wittmann |first8=Axel |date=26 January 2010 |title=Origin and emplacement of the impact formations at Chicxulub, Mexico, as revealed by the ICDP deep drilling at Yaxcopoil-1 and by numerical modeling |journal=[[Meteoritics & Planetary Science]] |language=en |volume=39 |issue=7 |pages=1035–1067 |doi=10.1111/j.1945-5100.2004.tb01128.x |doi-access=free |issn=1086-9379}}</ref> In March 2010, an international panel of 41 scientists reviewed 20 years of scientific literature and endorsed the asteroid hypothesis, specifically the Chicxulub impact, as the cause of the extinction, ruling out other theories such as massive [[volcanism]]. They had determined that a {{convert|10|to|15|km|mi|0|adj=mid|-wide|sp=us}} asteroid hurtled into Earth at Chicxulub on Mexico's Yucatán Peninsula.<ref name="Schulte10" /> Additional evidence for the impact event is found at the [[Tanis (fossil site)|Tanis site]] in southwestern [[North Dakota]], [[United States]].<ref name="pnas1">{{Cite journal |last1=Depalma |first1=Robert A. |last2=Smit |first2=Jan |last3=Burnham |first3=David A. |last4=Kuiper |first4=Klaudia |last5=Manning |first5=Phillip L. |last6=Oleinik |first6=Anton |last7=Larson |first7=Peter |last8=Maurrasse |first8=Florentin J. |last9=Vellekoop |first9=Johan |last10=Richards |first10=Mark A. |last11=Gurche |first11=Loren |last12=Alvarez |first12=Walter |year=2019 |title=A seismically induced onshore surge deposit at the KPG boundary, North Dakota |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=116 |issue=17 |pages=8190–8199 |bibcode=2019PNAS..116.8190D |doi=10.1073/pnas.1817407116 |pmc=6486721 |pmid=30936306 |doi-access=free}}</ref> Tanis is part of the heavily studied [[Hell Creek Formation]], a group of rocks spanning four states in North America renowned for many significant [[fossil]] discoveries from the [[Upper Cretaceous]] and lower [[Paleocene]].<ref>{{cite web |title=National Natural Landmarks – National Natural Landmarks (U.S. National Park Service) |url=https://www.nps.gov/subjects/nnlandmarks/site.htm?Site=HECR-MT |access-date=2019-03-22 |website=www.nps.gov |quote=Year designated: 1966}}</ref> Tanis is an extraordinary and unique site because it appears to record the events from the first minutes until a few hours after the impact of the giant [[Chicxulub crater|Chicxulub asteroid]] in extreme detail.<ref name="smit 2017">Smit, J., ''et al.'' (2017) [https://gsa.confex.com/gsa/2017AM/webprogram/Paper305713.html Tanis, a mixed marine-continental event deposit at the KPG Boundary in North Dakota caused by a seiche triggered by seismic waves of the Chicxulub Impact] Paper No. 113–15, presented 23 October 2017 at the GSA Annual Meeting, Seattle, Washington, USA.</ref><ref name="DePalma2017">DePalma, R. ''et al.'' (2017) [https://gsa.confex.com/gsa/2017AM/webprogram/Paper305627.html Life after impact: A remarkable mammal burrow from the Chicxulub aftermath in the Hell Creek Formation, North Dakota] Paper No. 113–16, presented 23 October 2017 at the GSA Annual Meeting, Seattle, Washington, USA.</ref> Amber from the site has been reported to contain [[Tektite|microtektites]] matching those of the Chicxulub impact event.<ref>{{cite book |last1=Kaskes |first1=P. |url=https://cris.vub.be/ws/portalfiles/portal/48767201/5090_Kaskes_et_al._2019_Abstract_Tanis_spherules_FINAL.pdf |title=Large Meteorite Impacts VI 2019 (LPI Contrib. No. 2136) |last2=Goderis |first2=S. |last3=Belza |first3=J. |last4=Tack |first4=P. |last5=DePalma |first5=R. A. |last6=Smit |first6=J. |last7=Vincze |first7=Laszlo |last8=Vabgaecje |first8=F. |last9=Claeys |first9=P. |publisher=Houston, TX: Lunar and Planetary Institute |year=2019 |volume=6 |pages=1–2 |chapter=Caught in amber: Geochemistry and petrography of uniquely preserved Chicxulub microtektites from the Tanis K-Pg site from North Dakota (USA) |access-date=11 April 2021 |number=Abstract 5085}}</ref>  Some researchers question the interpretation of the findings at the site or are skeptical of the team leader, Robert DePalma, who had not yet received his Ph.D. in geology at the time of the discovery and whose commercial activities have been regarded with suspicion.<ref>{{cite journal |last1=Barras |first1=Colin |date=5 April 2019 |title=Does fossil site record dino-killing impact? |journal=[[Science (journal)|Science]] |volume=364 |issue=6435 |pages=10–11 |bibcode=2019Sci...364...10B |doi=10.1126/science.364.6435.10 |pmid=30948530 |s2cid=96434764}}</ref> Furthermore, indirect evidence of an asteroid impact as the cause of the mass extinction comes from patterns of turnover in marine plankton.<ref>{{Cite journal |last1=Alegret |first1=Laia |last2=Molina |first2=Eustoquio |last3=Thomas |first3=Ellen |date=July 2003 |title=Benthic foraminiferal turnover across the Cretaceous/Paleogene boundary at Agost (southeastern Spain): paleoenvironmental inferences |journal=Marine Micropaleontology |language=en |volume=48 |issue=3–4 |pages=251–279 |doi=10.1016/S0377-8398(03)00022-7 |bibcode=2003MarMP..48..251A}}</ref>

[[File:Trinlake2.JPG|thumb|alt=rock striations with dark light boundary and surveying rod|The K–Pg boundary exposure in [[Trinidad Lake State Park]], in the [[Raton Basin]] of [[Colorado]], shows an abrupt change from dark- to light-colored rock.]]

{{location map| North America|relief=1|float=right|upright=1.8|caption=Location of Chicxulub crater, Mexico| lat=21.4|long=-89.5}}
[[File:Chicxulub radar topography.jpg|thumb|alt=topographic diagram showing round geographic features|Radar topography reveals the {{convert|180|km|0|abbr=on|adj=mid}}-wide ring of the [[Chicxulub crater]].]]Some critics of the impact theory have put forward that the impact precedes the mass extinction by about 300,000 years and thus was not its cause.<ref name="Keller">{{cite journal |author1=Keller, G. |author2=Adatte, T. |author3=Stinnesbeck, W. |author4=Rebolledo-Vieyra, M. |author5=Fucugauchi, J. U. |author6=Kramar, U. |author7=Stüben, D. |year=2004 |title=Chicxulub impact predates the K–T boundary mass extinction |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=101 |issue=11 |pages=3753–3758 |doi=10.1073/pnas.0400396101 |doi-access=free |pmc=374316 |pmid=15004276 |bibcode=2004PNAS..101.3753K}}</ref><ref>{{Cite journal |last1=Keller |first1=Gerta |last2=Adatte |first2=Thierry |last3=Stinnesbeck |first3=Wolfgang |last4=STüBEN |first4=Doris |last5=Berner |first5=Zsolt |last6=Kramar |first6=Utz |last7=Harting |first7=Markus |date=26 January 2010 |title=More evidence that the Chicxulub impact predates the K/T mass extinction |journal=[[Meteoritics & Planetary Science]] |language=en |volume=39 |issue=7 |pages=1127–1144 |doi=10.1111/j.1945-5100.2004.tb01133.x |doi-access=free |issn=1086-9379}}</ref> However, in a 2013 paper, [[Paul Renne]] of the [[Berkeley Geochronology Center]] dated the impact at {{nowrap|{{val|66.043|0.011}} million}} years ago, based on [[argon–argon dating]]. He further posits that the mass extinction occurred within 32,000&nbsp;years of this date.<ref>{{cite news |first=David |last=Perlman |website=sfgate.com |url=http://www.sfgate.com/science/article/Dinosaur-extinction-battle-flares-4261978.php |title=Dinosaur extinction battle flares |access-date=2013-02-08 |archive-url=https://web.archive.org/web/20130208122400/http://www.sfgate.com/science/article/Dinosaur-extinction-battle-flares-4261978.php |archive-date=2013-02-08 |url-status=live}}</ref> The dating of hydrothermally altered structures around the crater is consistent with this timeline.<ref>{{Cite journal |last1=Timms |first1=Nicholas E. |last2=Kirkland |first2=Christopher L. |last3=Cavosie |first3=Aaron J. |last4=Rae |first4=Auriol S.P. |last5=Rickard |first5=William D.A. |last6=Evans |first6=Noreen J. |last7=Erickson |first7=Timmons M. |last8=Wittmann |first8=Axel |last9=Ferrière |first9=Ludovic |last10=Collins |first10=Gareth S. |last11=Gulick |first11=Sean P.S. |date=15 July 2020 |title=Shocked titanite records Chicxulub hydrothermal alteration and impact age |journal=[[Geochimica et Cosmochimica Acta]] |language=en |volume=281 |pages=12–30 |doi=10.1016/j.gca.2020.04.031 |doi-access=free}}</ref>

In 2007, it was proposed that the impactor belonged to the [[Baptistina family]] of asteroids.<ref name="bottke2007">{{cite journal |author1=Bottke, W. F. |author2=Vokrouhlický, D. |author3=Nesvorný, D. |s2cid=4322622 |date=September 2007 |title=An asteroid breakup 160 Myr ago as the probable source of the K/T impactor |journal=[[Nature (journal)|Nature]] |volume=449 |issue=7158 |pages=48–53 |pmid=17805288 |doi=10.1038/nature06070 |bibcode=2007Natur.449...48B}}</ref> This link has been doubted, though not disproved, in part because of a lack of observations of the asteroid and its family.<ref name="majaess2008">{{cite journal |author1=Majaess, D. J. |author2=Higgins, D. |author3=Molnar, L. A. |author4=Haegert, M. J. |author5=Lane, D. J. |author6=Turner, D. G. |author7=Nielsen, I. |title=New constraints on the asteroid 298 Baptistina, the alleged family member of the K/T impactor |journal=[[The Journal of the Royal Astronomical Society of Canada]] |date=February 2009 |volume=103 |issue=1 |pages=7–10 |bibcode=2009JRASC.103....7M |arxiv=0811.0171 }}</ref> It was reported in 2009 that 298 Baptistina does not share the chemical signature of the K–Pg impactor.<ref name="reddy2008">{{cite journal |author1=Reddy, V. |author2=Emery, J. P. |author3=Gaffey, M. J. |author4=Bottke, W. F. |author5=Cramer, A. |author6=Kelley, M. S. |title=Composition of 298 Baptistina: Implications for the K/T impactor link |journal=[[Meteoritics & Planetary Science]] |volume=44 |issue=12 |pages=1917–1927 |date=December 2009 |doi=10.1111/j.1945-5100.2009.tb02001.x |doi-access=free |bibcode=2009M&PS...44.1917R|citeseerx=10.1.1.712.8165 |s2cid=39644763}}</ref> Further, a 2011 [[Wide-field Infrared Survey Explorer]] (WISE) study of reflected light from the asteroids of the family estimated their break-up at 80 Ma, giving them insufficient time to shift orbits and impact Earth by 66 Ma.<ref>{{cite news |title=NASA's WISE raises doubt about asteroid family believed responsible for dinosaur extinction |date=20 September 2011 |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2011/09/110919144042.htm |access-date=21 September 2011 |archive-url=https://web.archive.org/web/20110923215602/http://www.sciencedaily.com/releases/2011/09/110919144042.htm |archive-date=23 September 2011 |url-status=live}}</ref>

==== Effects of impact ====
[[File:Chicxulub impact - artist impression.jpg|thumb|right|Artistic impression of the asteroid slamming into tropical, shallow seas of the sulfur-rich [[Yucatán Peninsula]] in what is today [[Geography of Mexico|Southeast Mexico]].<ref name="nhm.ac.uk">{{cite web |last=Osterloff |first=Emily |date=2018 |title=How an asteroid ended the age of the dinosaurs |url=https://www.nhm.ac.uk/discover/how-an-asteroid-caused-extinction-of-dinosaurs.html |url-status=live |location=[[London]] |publisher=[[Natural History Museum, London|Natural History Museum]] |archive-url=https://web.archive.org/web/20220426174952/https://www.nhm.ac.uk/discover/how-an-asteroid-caused-extinction-of-dinosaurs.html |archive-date=26 April 2022 |access-date=18 May 2022}}</ref> The aftermath of this immense asteroid collision, which occurred approximately 66 million years ago, is believed to have caused the [[Extinction event|mass extinction]] of non-avian dinosaurs and many other species on Earth.<ref name="nhm.ac.uk"/> The impact spewed hundreds of billions of tons of sulfur into the atmosphere, producing a worldwide blackout and freezing temperatures which persisted for at least a decade.<ref name="nhm.ac.uk"/>]]

The collision would have released the same energy as {{convert|100|TtTNT|J|lk=on|abbr=off}}—more than a billion times the energy of the [[atomic bombings of Hiroshima and Nagasaki]].<ref name="Schulte10" /> The Chicxulub impact caused a global catastrophe. Some of the phenomena were brief occurrences immediately following the impact, but there were also long-term geochemical and climatic disruptions that devastated the ecology.<ref name="Robertson Lewis Sheehan 2013"/><ref name="Pope">{{cite journal |author1=Pope, K. O. |author2=d'Hondt, S. L. |author3=Marshall. C. R. |year=1998 |title=Meteorite impact and the mass extinction of species at the Cretaceous/Tertiary boundary |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=95 |issue=19 |pages=11028–11029 |bibcode=1998PNAS...9511028P |doi=10.1073/pnas.95.19.11028 |pmc=33889 |pmid=9736679 |doi-access=free}}</ref><ref name="Brugger Feulner Petri 2016"/>

The scientific consensus is that the asteroid impact at the K–Pg boundary left [[megatsunami]] deposits and sediments around the area of the Caribbean Sea and Gulf of Mexico, from the colossal waves created by the impact.<ref>{{cite book |author=Bourgeois, J. |series=The Sea (Ideas and Observations on Progress in the Study of the Seas) |publisher=Harvard University |year=2009 |isbn=978-0-674-03173-9 |editor1=Robinson, A.R. |volume=15 |title=Tsunamis |location=Boston, MA |chapter=Chapter&nbsp;3. Geologic effects and records of tsunamis |access-date=2012-03-29 |editor2=Bernard, E.N. |chapter-url=http://faculty.washington.edu/jbourgeo/BourgeoisTheSeaCh3.pdf}}</ref> These deposits have been identified in the La Popa basin in northeastern Mexico,<ref>{{cite journal |author1=Lawton, T. F. |author2=Shipley, K. W. |author3=Aschoff, J. L. |author4=Giles, K. A. |author5=Vega, F. J. |year=2005 |title=Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, northeastern Mexico, and its implications for distribution of impact-related deposits flanking the Gulf of Mexico |journal=Geology |volume=33 |issue=2 |pages=81–84 |bibcode=2005Geo....33...81L |doi=10.1130/G21057.1}}</ref> platform carbonates in northeastern Brazil,<ref>{{cite journal |author1=Albertão, G. A. |author2=P. P. Martins Jr. |year=1996 |title=A possible tsunami deposit at the Cretaceous-Tertiary boundary in Pernambuco, northeastern Brazil |url=http://www.repositorio.ufop.br/handle/123456789/4089 |journal=Sed. Geol. |volume=104 |issue=1–4 |pages=189–201 |bibcode=1996SedG..104..189A |doi=10.1016/0037-0738(95)00128-X}}</ref> in [[Atlantic Ocean|Atlantic]] deep-sea sediments,<ref>{{cite journal |author1=Norris, R. D. |author2=Firth, J. |author3=Blusztajn, J. S. |author4=Ravizza, G. |name-list-style=amp |year=2000 |title=Mass failure of the North Atlantic margin triggered by the Cretaceous-Paleogene bolide impact |journal=[[Geology (journal)|Geology]] |volume=28 |issue=12 |pages=1119–1122 |bibcode=2000Geo....28.1119N |doi=10.1130/0091-7613(2000)28<1119:MFOTNA>2.0.CO;2}}</ref> and in the form of the thickest-known layer of graded sand deposits, around {{cvt|100|m||||}}, in the Chicxulub crater itself, directly above the shocked granite ejecta. The [[megatsunami]] has been estimated at more than {{cvt|100|m||||}} tall, as the asteroid fell into relatively shallow seas; in deep seas it would have been {{convert|4.6|km|abbr=on}} tall.<ref>{{cite book |last=Bryant |first=Edward |url=https://books.google.com/books?id=tOkpBAAAQBAJ&pg=PA178 |title=Tsunami: The Underrated Hazard |date=June 2014 |publisher=Springer |isbn=978-3-319-06133-7 |page=178 |access-date=2017-08-30 |archive-url=https://web.archive.org/web/20190901055132/https://books.google.com/books?id=tOkpBAAAQBAJ&pg=PA178&lpg=PA17 |archive-date=2019-09-01 |url-status=live}}</ref> Fossiliferous sedimentary rocks deposited during the K–Pg impact have been found in the Gulf of Mexico area, including tsunami wash deposits carrying remains of a [[mangrove]]-type ecosystem, indicating that water in the Gulf of Mexico sloshed back and forth repeatedly after the impact; dead fish left in these shallow waters were not disturbed by scavengers.<ref>{{cite journal |last1=Smit |first1=Jan |last2=Montanari |first2=Alessandro |last3=Swinburne |first3=Nicola H. |last4=Alvarez |first4=Walter |last5=Hildebrand |first5=Alan R. |last6=Margolis |first6=Stanley V. |last7=Claeys |first7=Philippe |last8=Lowrie |first8=William |last9=Asaro |first9=Frank |year=1992 |title=Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico |journal=[[Geology (journal)|Geology]] |volume=20 |issue=2 |pages=99–103 |bibcode=1992Geo....20...99S |doi=10.1130/0091-7613(1992)020<0099:TBDWCU>2.3.CO;2 |pmid=11537752}}</ref><ref>{{cite book |url=https://www.lpi.usra.edu/lpi/contribution_docs/LPI-000827.pdf |title=Field guide to Cretaceous-tertiary boundary sections in northeastern Mexico |date=1994 |publisher=[[Lunar and Planetary Institute]] |access-date=2019-06-25 |archive-url=https://web.archive.org/web/20190821130759/https://www.lpi.usra.edu/lpi/contribution_docs/LPI-000827.pdf |archive-date=2019-08-21 |url-status=live}}</ref><ref>{{cite journal |last1=Smit |first1=Jan |year=1999 |title=The global stratigraphy of the Cretaceous-Tertiary boundary impact ejecta |journal=[[Annual Review of Earth and Planetary Sciences]] |volume=27 |pages=75–113 |bibcode=1999AREPS..27...75S |doi=10.1146/annurev.earth.27.1.75}}</ref><ref>{{cite journal |last=Kring |first=David A. |year=2007 |title=The Chicxulub impact event and its environmental consequences at the Cretaceous-Tertiary boundary |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=255 |issue=1–2 |pages=4–21 |bibcode=2007PPP...255....4K |doi=10.1016/j.palaeo.2007.02.037}}</ref><ref>{{cite web |url=https://www.lpi.usra.edu/science/kring/Chicxulub/regional-effects/ |title=Chicxulub impact event |url-status=live |archive-url=https://web.archive.org/web/20190726023401/https://www.lpi.usra.edu/science/kring/Chicxulub/regional-effects/ |archive-date=2019-07-26 |access-date=2019-06-25 |website=www.lpi.usra.edu}}</ref>

The re-entry of ejecta into Earth's atmosphere included a brief (hours-long) but intense pulse of [[infrared|infrared radiation]], cooking exposed organisms.<ref name="Robertson" /> This is debated, with opponents arguing that local ferocious fires, probably limited to North America, fall short of global [[firestorm]]s. This is the "[[nuclear winter#Potential climatic precedents|Cretaceous–Paleogene firestorm debate]]". A paper in 2013 by a prominent modeler of [[nuclear winter]] suggested that, based on the amount of soot in the global debris layer, the entire terrestrial [[biosphere]] might have burned, implying a global soot-cloud blocking out the sun and creating an [[impact winter]] effect.<ref name="Robertson Lewis Sheehan 2013">{{cite journal |author1=Robertson, D. S. |author2=Lewis, W. M. |author3=Sheehan, P. M. |author4=Toon, O. B. |year=2013 |title=K/Pg extinction: Re-evaluation of the heat/fire hypothesis |journal=[[Journal of Geophysical Research]] |volume=118 |issue=1 |pages=329–336 |bibcode=2013JGRG..118..329R |doi=10.1002/jgrg.20018|doi-access=free }}</ref> If widespread fires occurred this would have exterminated the most vulnerable organisms that survived the period immediately after the impact.<ref>{{cite journal |title=Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact |author1=Pope, K.O. |author2=Baines, K.H. |author3=Ocampo, A.C. |author4=Ivanov, B. A. |year=1997 |journal=[[Journal of Geophysical Research]] |volume=102 |issue=E9 |pages=21645–21664 |doi=10.1029/97JE01743 |pmid=11541145 |bibcode=1997JGR...10221645P|doi-access=free }}</ref> Experimental analysis suggests that any impact-induced wildfires were insufficient on their own to cause plant extinctions,<ref>{{Cite journal |last1=Belcher |first1=Claire M. |last2=Hadden |first2=Rory M. |last3=Rein |first3=Guillermo |last4=Morgan |first4=Joanna V. |last5=Artemieva |first5=Natalia |last6=Goldin |first6=Tamara |date=22 January 2015 |title=An experimental assessment of the ignition of forest fuels by the thermal pulse generated by the Cretaceous–Palaeogene impact at Chicxulub |journal=[[Journal of the Geological Society]] |language=en |volume=172 |issue=2 |pages=175–185 |doi=10.1144/jgs2014-082 |doi-access=free |issn=0016-7649 |hdl=10044/1/18936 |hdl-access=free}}</ref> and much of the thermal radiation generated by the impact would have been absorbed by the atmosphere and ejecta in the lower atmosphere.<ref>{{Cite journal |last=Adair |first=Robert K. |date=1 June 2010 |title=Wildfires and animal extinctions at the Cretaceous/Tertiary boundary |journal=[[American Journal of Physics]] |volume=78 |issue=6 |pages=567–573 |doi=10.1119/1.3192770 |issn=0002-9505 |url=https://pubs.aip.org/ajp/article/78/6/567/1042048/Wildfires-and-animal-extinctions-at-the-Cretaceous |language=en |access-date=22 August 2024}}</ref>

Aside from the hypothesized fire effects on reduction of insolation, the impact would have created a humongous dust cloud that blocked sunlight for up to a year, inhibiting photosynthesis.<ref>{{Cite journal |last1=Morgan |first1=Joanna V. |last2=Bralower |first2=Timothy J. |last3=Brugger |first3=Julia |last4=Wünnemann |first4=Kai |date=12 April 2022 |title=The Chicxulub impact and its environmental consequences |url=https://www.nature.com/articles/s43017-022-00283-y |journal=[[Nature Reviews Earth & Environment]] |language=en |volume=3 |issue=5 |pages=338–354 |doi=10.1038/s43017-022-00283-y |issn=2662-138X |access-date=22 August 2024}}</ref><ref name=":11" /><ref name="Pope" /> The asteroid hit an area of [[gypsum]] and [[anhydrite]] rock containing a large amount of combustible hydrocarbons and sulfur,<ref>{{cite journal |last1=Kaiho |first1=Kunio |last2=Oshima |first2=Naga |year=2017 |title=Site of asteroid impact changed the history of life on Earth: The low probability of mass extinction |journal=Scientific Reports |volume=7 |issue=1 |at=Article number 14855 |bibcode=2017NatSR...714855K |doi=10.1038/s41598-017-14199-x |pmc=5680197 |pmid=29123110}}</ref> much of which was vaporized, thereby injecting [[sulfuric acid]] [[aerosol]]s into the [[stratosphere]], which might have reduced sunlight reaching the Earth's surface by more than 50%.<ref name="Ohno 2014">{{cite journal |last1=Ohno |first1=S. |last2=Kadono |first2=T. |last3=Kurosawa |first3=K. |last4=Hamura |first4=T. |last5=Sakaiya |first5=T. |last6=Shigemori |first6=K. |last7=Hironaka |first7=Y. |last8=Sano |first8=T. |last9=Watari |first9=T. |last10=Otani |first10=K. |last11=Matsui |first11=T. |last12=Sugita |first12=S. |display-authors=3 |date=2014 |title=Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification |journal=[[Nature Geoscience]] |volume=7 |issue=4 |pages=279–282 |bibcode=2014NatGe...7..279O |doi=10.1038/ngeo2095}}</ref> Fine silicate dust also contributed to the intense impact winter,<ref>{{Cite journal |last1=Senel |first1=Cem Berk |last2=Kaskes |first2=Pim |last3=Temel |first3=Orkun |last4=Vellekoop |first4=Johan |last5=Goderis |first5=Steven |last6=DePalma |first6=Robert |last7=Prins |first7=Maarten A. |last8=Claeys |first8=Philippe |last9=Karatekin |first9=Özgür |date=30 October 2023 |title=Chicxulub impact winter sustained by fine silicate dust |journal=[[Nature Geoscience]] |language=en |volume=16 |issue=11 |pages=1033–1040 |doi=10.1038/s41561-023-01290-4 |bibcode=2023NatGe..16.1033S |s2cid=264805571 |issn=1752-0894}}</ref> as did soot from wildfires.<ref>{{Cite journal |last1=Bardeen |first1=Charles G. |last2=Garcia |first2=Rolando R. |last3=Toon |first3=Owen B. |last4=Conley |first4=Andrew J. |date=21 August 2017 |title=On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections |journal=[[Proceedings of the National Academy of Sciences of the United States]] |language=en |volume=114 |issue=36 |pages=E7415–E7424 |doi=10.1073/pnas.1708980114 |doi-access=free |issn=0027-8424 |pmc=5594694 |pmid=28827324 }}</ref><ref>{{Cite journal |last1=Lyons |first1=Shelby L. |last2=Karp |first2=Allison T. |last3=Bralower |first3=Timothy J. |last4=Grice |first4=Kliti |last5=Schaefer |first5=Bettina |last6=Gulick |first6=Sean P. S. |last7=Morgan |first7=Joanna V. |last8=Freeman |first8=Katherine H. |date=28 September 2020 |title=Organic matter from the Chicxulub crater exacerbated the K–Pg impact winter |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |language=en |volume=117 |issue=41 |pages=25327–25334 |doi=10.1073/pnas.2004596117 |doi-access=free |issn=0027-8424 |pmc=7568312 |pmid=32989138 |bibcode=2020PNAS..11725327L }}</ref><ref>{{Cite journal |last1=Kaiho |first1=Kunio |last2=Oshima |first2=Naga |last3=Adachi |first3=Kouji |last4=Adachi |first4=Yukimasa |last5=Mizukami |first5=Takuya |last6=Fujibayashi |first6=Megumu |last7=Saito |first7=Ryosuke |date=14 July 2016 |title=Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction |journal=[[Scientific Reports]] |language=en |volume=6 |issue=1 |pages=28427 |doi=10.1038/srep28427 |pmid=27414998 |pmc=4944614 |bibcode=2016NatSR...628427K |issn=2045-2322 }}</ref> The climatic forcing of this impact winter was about 100 times more potent than that of the [[1991 eruption of Mount Pinatubo]].<ref>{{Cite journal |last1=Pierazzo |first1=Elisabetta |last2=Hahmann |first2=Andrea N. |last3=Sloan |first3=Lisa C. |date=5 July 2004 |title=Chicxulub and Climate: Radiative Perturbations of Impact-Produced S-Bearing Gases |journal=[[Astrobiology (journal)|Astrobiology]] |language=en |volume=3 |issue=1 |pages=99–118 |doi=10.1089/153110703321632453 |pmid=12804368 |issn=1531-1074}}</ref> According to models of the [[Hell Creek Formation]], the onset of global darkness would have reached its maximum in only a few weeks and likely lasted upwards of 2 years.<ref name=":2" /> Freezing temperatures probably lasted for at least three years.<ref name="Brugger Feulner Petri 2016">{{cite journal |author1=Brugger, Julia |author2=Feulner, Georg |author3=Petri, Stefan |year=2016 |title=Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous |journal=[[Geophysical Research Letters]] |volume=44 |issue=1 |pages=419–427 |doi=10.1002/2016GL072241 |bibcode=2017GeoRL..44..419B |url=https://publications.pik-potsdam.de/pubman/item/item_21282_1/component/file_21283/7402oa.pdf |s2cid=53631053}}</ref> At Brazos section, the [[sea surface temperature]] dropped as much as {{cvt|7|C-change}} for decades after the impact.<ref name=":11"/> It would take at least ten years for such aerosols to dissipate, and would account for the extinction of plants and phytoplankton, and subsequently herbivores and their [[Predation|predators]]. Creatures whose food chains were based on [[detritus]] would have a reasonable chance of survival.<ref name="springerlink.com" /><ref name="Pope" /> In 2016, a scientific drilling project obtained deep rock-[[core sample]]s from the [[Peak ring (crater)|peak ring]] around the Chicxulub impact crater. The discoveries confirmed that the rock comprising the peak ring had been shocked by immense pressure and melted in just minutes from its usual state into its present form. Unlike sea-floor deposits, the peak ring was made of granite originating much deeper in the earth, which had been ejected to the surface by the impact. [[Gypsum]] is a [[sulfate]]-containing rock usually present in the shallow seabed of the region; it had been almost entirely removed, vaporized into the atmosphere. The impactor was large enough to create a {{convert|120|mi|km|adj=mid|-wide|order=flip|sp=us}} peak ring, to melt, shock, and eject deep granite, to create colossal water movements, and to eject an immense quantity of vaporized rock and sulfates into the atmosphere, where they would have persisted for several years. This worldwide dispersal of dust and sulfates would have affected climate catastrophically, led to large temperature drops, and devastated the food chain.<ref>{{cite journal |last1=Hand |first1=Eric |date=17 November 2016 |title=Updated: Drilling of dinosaur-killing impact crater explains buried circular hills |journal=Science |doi=10.1126/science.aaf5684}}</ref><ref>{{cite news |date=2016-11-18 |title=Chicxulub crater dinosaur extinction |newspaper=[[The New York Times]] |location=New York, NY |url=https://www.nytimes.com/2016/11/18/science/chicxulub-crater-dinosaur-extinction.html |access-date=2017-10-14 |archive-url=https://web.archive.org/web/20171109221221/https://www.nytimes.com/2016/11/18/science/chicxulub-crater-dinosaur-extinction.html |archive-date=2017-11-09 |url-status=live}}</ref>

The release of large quantities of sulphur aerosols into the atmosphere as a consequence of the impact would also have caused acid rain.<ref name=":9">{{Cite journal |last1=Sigurdsson |first1=H. |last2=D'Hondt |first2=S. |last3=Carey |first3=S. |date=April 1992 |title=The impact of the Cretaceous/Tertiary bolide on evaporite terrane and generation of major sulfuric acid aerosol |journal=[[Earth and Planetary Science Letters]] |language=en |volume=109 |issue=3–4 |pages=543–559 |doi=10.1016/0012-821X(92)90113-A |bibcode=1992E&PSL.109..543S}}</ref><ref name="Ohno 2014" /> Oceans acidified as a result.<ref name="NYT-20191021" /><ref name="PNAS-20191021" /> This decrease in ocean pH would kill many organisms that grow shells of [[calcium carbonate]].<ref name="Ohno 2014" /> The heating of the atmosphere during the impact itself may have also generated [[nitric acid]] rain through the production of nitrogen oxides and their subsequent reaction with water vapour.<ref>{{Cite journal |last1=Prinn |first1=Ronald G. |last2=Fegley |first2=Bruce |date=May 1987 |title=Bolide impacts, acid rain, and biospheric traumas at the Cretaceous-Tertiary boundary |journal=[[Earth and Planetary Science Letters]] |language=en |volume=83 |issue=1–4 |pages=1–15 |doi=10.1016/0012-821X(87)90046-X |bibcode=1987E&PSL..83....1P}}</ref><ref name=":9" />

After the impact winter, the Earth entered a period of global warming as a result of the vapourisation of carbonates into carbon dioxide, whose long residence time in the atmosphere ensured significant warming would occur after more short-lived cooling gases dissipated.<ref>{{Cite journal |last1=Pope |first1=Kevin O. |last2=Baines |first2=Kevin H. |last3=Ocampo |first3=Adriana C. |last4=Ivanov |first4=Boris A. |date=December 1994 |title=Impact winter and the Cretaceous/Tertiary extinctions: Results of a Chicxulub asteroid impact model |journal=[[Earth and Planetary Science Letters]] |language=en |volume=128 |issue=3–4 |pages=719–725 |doi=10.1016/0012-821X(94)90186-4 |pmid=11539442 |bibcode=1994E&PSL.128..719P}}</ref> Carbon monoxide concentrations also increased and caused particularly devastating global warming because of the consequent increases in [[tropospheric ozone]] and methane concentrations.<ref>{{Cite journal |last1=Kawaragi |first1=Ko |last2=Sekine |first2=Yasuhito |last3=Kadono |first3=Toshihiko |last4=Sugita |first4=Seiji |last5=Ohno |first5=Sohsuke |last6=Ishibashi |first6=Ko |last7=Kurosawa |first7=Kosuke |last8=Matsui |first8=Takafumi |last9=Ikeda |first9=Susumu |date=30 May 2009 |title=Direct measurements of chemical composition of shock-induced gases from calcite: an intense global warming after the Chicxulub impact due to the indirect greenhouse effect of carbon monoxide |journal=[[Earth and Planetary Science Letters]] |language=en |volume=282 |issue=1–4 |pages=56–64 |doi=10.1016/j.epsl.2009.02.037 |bibcode=2009E&PSL.282...56K}}</ref> The impact's injection of water vapour into the atmosphere also produced major climatic perturbations.<ref>{{Cite journal |last1=Pierazzo |first1=Elisabetta |last2=Kring |first2=David A. |last3=Melosh |first3=H. Jay |date=25 November 1998 |title=Hydrocode simulation of the Chicxulub impact event and the production of climatically active gases |journal=[[Journal of Geophysical Research: Planets]] |language=en |volume=103 |issue=E12 |pages=28607–28625 |doi=10.1029/98JE02496 |bibcode=1998JGR...10328607P |issn=0148-0227}}</ref>

The end-Cretaceous event is the only [[Extinction event|mass extinction]] definitively known to be associated with an impact, and other large extraterrestrial impacts, such as the [[Manicouagan Reservoir]] impact, do not coincide with any noticeable extinction events.<ref>{{cite book |last=Brannen |first=Peter |title=The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and Our Quest to Understand Earth's Past Mass Extinctions |date=2017 |publisher=Harper Collins |isbn=978-0-06-236480-7 |page=336}}</ref>

[[File:Moody Creek Mine 7 Mile Creek Waimatuku Dunollie New Zealand.jpg|thumb|The river bed at the Moody Creek Mine, 7 Mile Creek / Waimatuku, Dunollie, New Zealand contains evidence of a devastating event on terrestrial plant communities at the Cretaceous–Paleogene boundary, confirming the severity and global nature of the event.<ref name="Vajdaetal"/>]]

=== Multiple impact event ===
Other crater-like topographic features have also been proposed as impact craters formed in connection with Cretaceous–Paleogene extinction. This suggests the possibility of near-simultaneous multiple impacts, perhaps from a fragmented asteroidal object similar to the [[Comet Shoemaker–Levy 9|Shoemaker–Levy 9]] impact with [[Jupiter]]. In addition to the {{convert|180|km|abbr=on|adj=on}} [[Chicxulub crater]], there is the {{convert|24|km|mi|abbr=on|adj=on}} [[Boltysh crater]] in [[Ukraine]] ({{val|65.17|0.64|u=Ma}}), the {{convert|20|km|mi|abbr=on|adj=on}} [[Silverpit crater]] in the [[North Sea]] ({{val|59.5|14.5|u=Ma}}) possibly formed by [[bolide]] impact, and the controversial and much larger {{convert|600|km|mi|abbr=on|adj=on}} [[Shiva crater]]. Any other craters that might have formed in the [[Tethys Ocean]] would since have been obscured by the northward tectonic drift of Africa and India.<ref>{{cite journal |author=Mullen, L. |date=October 13, 2004 |title=Debating the Dinosaur Extinction |url=http://www.astrobio.net/exclusive/1243/debating-the-dinosaur-extinction |journal=Astrobiology Magazine |archive-url=https://web.archive.org/web/20120625152542/http://www.astrobio.net/exclusive/1243/debating-the-dinosaur-extinction |archive-date=June 25, 2012 |access-date=2012-03-29}}</ref><ref>{{cite journal |author=Mullen, L. |date=October 20, 2004 |title=Multiple impacts |url=http://www.astrobio.net/exclusive/1253/multiple-impacts |journal=Astrobiology Magazine |archive-url=https://web.archive.org/web/20120406162059/http://www.astrobio.net/exclusive/1253/multiple-impacts |archive-date=April 6, 2012 |access-date=2012-03-29}}</ref><ref name="Mullen Shiva">{{cite journal |author=Mullen, L. |date=November 3, 2004 |title=Shiva: Another K–T impact? |url=http://www.astrobio.net/exclusive/1281/shiva-another-k-t-impact |journal=[[Astrobiology Magazine]] |archive-url=https://web.archive.org/web/20111211091219/http://www.astrobio.net/exclusive/1281/shiva-another-k-t-impact |archive-date=December 11, 2011 |access-date=2012-03-29}}</ref><ref name="chatterjee 1997">{{cite book |last=Chatterjee |first=Sankar |title=30th International Geological Congress |date=August 1997 |isbn=978-90-6764-254-5 |volume=26 |pages=31–54 |chapter=Multiple Impacts at the KT Boundary and the Death of the Dinosaurs |author-link=Sankar Chatterjee |chapter-url=https://books.google.com/books?id=3IORF1Ei3LIC&pg=PA31}}</ref>

=== Deccan Traps ===
{{Main|Deccan Traps}}
The Deccan Traps, which erupted close to the boundary between the Mesozoic and Cenozoic,<ref>{{Cite journal |last=Kaneoka |first=Ichiro |date=January 1980 |title=40Ar/39Ar dating on volcanic rocks of the Deccan Traps, India |journal=[[Earth and Planetary Science Letters]] |language=en |volume=46 |issue=2 |pages=233–243 |doi=10.1016/0012-821X(80)90009-6}}</ref><ref name=":10">{{Cite journal |last1=Duncan |first1=R. A. |last2=Pyle |first2=D. G. |date=30 June 1988 |title=Rapid eruption of the Deccan flood basalts at the Cretaceous/Tertiary boundary |journal=[[Nature (journal)|Nature]] |language=en |volume=333 |issue=6176 |pages=841–843 |doi=10.1038/333841a0 |bibcode=1988Natur.333..841D |s2cid=4351454 |issn=0028-0836}}</ref><ref>{{Cite journal |last1=Courtillot |first1=V. |last2=Féraud |first2=G. |last3=Maluski |first3=H. |last4=Vandamme |first4=D. |last5=Moreau |first5=M. G. |last6=Besse |first6=J. |date=30 June 1988 |title=Deccan flood basalts and the Cretaceous/Tertiary boundary |journal=[[Nature (journal)|Nature]] |language=en |volume=333 |issue=6176 |pages=843–846 |doi=10.1038/333843a0 |bibcode=1988Natur.333..843C |s2cid=4326163 |issn=0028-0836}}</ref> have been cited as an alternate explanation for the mass extinction.<ref>{{Cite journal |last1=Courtillot |first1=Vincent |last2=Besse |first2=Jean |last3=Vandamme |first3=Didier |last4=Montigny |first4=Raymond |last5=Jaeger |first5=Jean-Jacques |last6=Cappetta |first6=Henri |date=November 1986 |title=Deccan flood basalts at the Cretaceous/Tertiary boundary? |journal=[[Earth and Planetary Science Letters]] |language=en |volume=80 |issue=3–4 |pages=361–374 |doi=10.1016/0012-821X(86)90118-4 |bibcode=1986E&PSL..80..361C}}</ref><ref>{{Cite journal |last=Courtillot |first=V. |date=December 1990 |title=Deccan volcanism at the Cretaceous-Tertiary boundary: past climatic crises as a key to the future? |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=89 |issue=3 |pages=291–299 |doi=10.1016/0031-0182(90)90070-N |bibcode=1990PPP....89..291C}}</ref> Before 2000, arguments that the [[Deccan Traps]] [[flood basalt]]s caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 Mya and lasted more than 2&nbsp;million years. The most recent evidence shows that the traps erupted over a period of only 800,000&nbsp;years spanning the K–Pg boundary, and therefore may be responsible for the extinction and the delayed biotic recovery thereafter.<ref>{{cite journal |author1=Keller, G. |author2=Adatte, T. |author3=Gardin, S. |author4=Bartolini, A. |author5=Bajpai, S. |title=Main Deccan volcanism phase ends near the K–T boundary: Evidence from the Krishna-Godavari Basin, SE India |year=2008 |doi=10.1016/j.epsl.2008.01.015 |journal=[[Earth and Planetary Science Letters]] |volume=268 |pages=293–311 |bibcode=2008E&PSL.268..293K |issue=3–4}}</ref>

The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulfuric aerosols into the air, which might have blocked sunlight and thereby reduced photosynthesis in plants.<ref>{{Cite journal |last1=Callegaro |first1=Sara |last2=Baker |first2=Don R. |last3=Renne |first3=Paul R. |last4=Melluso |first4=Leone |last5=Geraki |first5=Kalotina |last6=Whitehouse |first6=Martin J. |last7=De Min |first7=Angelo |last8=Marzoli |first8=Andrea |date=6 October 2023 |title=Recurring volcanic winters during the latest Cretaceous: Sulfur and fluorine budgets of Deccan Traps lavas |journal=[[Science Advances]] |language=en |volume=9 |issue=40 |pages=eadg8284 |doi=10.1126/sciadv.adg8284 |issn=2375-2548 |pmc=10550224 |pmid=37792933 |bibcode=2023SciA....9G8284C }}</ref> In addition, the latest Cretaceous saw a rise in global temperatures;<ref>{{Cite journal |last1=Nordt |first1=Lee |last2=Atchley |first2=Stacy |last3=Dworkin |first3=Steve |date=December 2003 |title=Terrestrial Evidence for Two Greenhouse Events in the Latest Cretaceous |journal=[[Geological Society of America Today]] |language=en |volume=13 |issue=12 |pages=4 |doi=10.1130/1052-5173(2003)013<4:TEFTGE>2.0.CO;2 |doi-access=free |issn=1052-5173}}</ref><ref>{{Cite journal |last1=Berggren |first1=W.A |last2=Aubry |first2=M.-P |last3=van Fossen |first3=M |last4=Kent |first4=D.V |last5=Norris |first5=R.D |last6=Quillévéré |first6=F |date=1 June 2000 |title=Integrated Paleocene calcareous plankton magnetobiochronology and stable isotope stratigraphy: DSDP Site 384 (NW Atlantic Ocean) |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=159 |issue=1–2 |pages=1–51 |doi=10.1016/S0031-0182(00)00031-6 |bibcode=2000PPP...159....1B}}</ref> Deccan Traps volcanism resulted in carbon dioxide emissions that increased the greenhouse effect when the dust and aerosols cleared from the atmosphere.<ref>{{Cite journal|title = A volcanic eruption|last = Courtillot|first = Vincent|date = 1990|journal = [[Scientific American]] |doi = 10.1038/scientificamerican1090-85|pmid = 11536474|pages = 85–92|volume = 263|issue = 4|bibcode = 1990SciAm.263d..85C}}</ref><ref name=":10" /> Plant fossils record a 250 ppm increase in carbon dioxide concentrations across the K-Pg boundary likely attributable to Deccan Traps activity.<ref>{{Cite journal |last1=Milligan |first1=Joseph N. |last2=Royer |first2=Dana L. |last3=Franks |first3=Peter J. |last4=Upchurch |first4=Garland R. |last5=McKee |first5=Melissa L. |date=7 March 2019 |title=No Evidence for a Large Atmospheric CO<sub>2</sub> Spike Across the Cretaceous-Paleogene Boundary |journal=[[Geophysical Research Letters]] |language=en |volume=46 |issue=6 |pages=3462–3472 |doi=10.1029/2018GL081215 |doi-access=free |issn=0094-8276}}</ref> The increased carbon dioxide emissions also caused acid rain, evidenced by increased mercury deposition due to increased solubility of mercury compounds in more acidic water.<ref>{{cite journal |last1=Sial |first1=A. N. |last2=Lacerda |first2=L. D. |last3=Ferreira |first3=V. P. |last4=Frei |first4=R. |last5=Marquillas |first5=R. A. |last6=Barbosa |first6=J. A. |last7=Gaucher |first7=C. |last8=Windmöller |first8=C. C. |last9=Pereira |first9=N. S. |date=1 October 2013 |title=Mercury as a proxy for volcanic activity during extreme environmental turnover: The Cretaceous–Paleogene transition |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=387 |pages=153–164 |doi=10.1016/j.palaeo.2013.07.019 |bibcode=2013PPP...387..153S|url=http://www.repositorio.ufc.br/handle/riufc/65773 }}</ref>

Evidence for extinctions caused by the Deccan Traps includes the reduction in diversity of marine life when the climate near the K–Pg boundary increased in temperature. The temperature increased about three to four degrees very rapidly between 65.4 and 65.2 million years ago, which is very near the time of the extinction event. Not only did the climate temperature increase, but the water temperature decreased, causing a drastic decrease in marine diversity.<ref>{{cite journal |last1=Keller |first1=Gerta |date=July 2001 |title=The end-cretaceous mass extinction in the marine realm: Year 2000 assessment |url=http://doc.rero.ch/record/14191/files/PAL_E1154.pdf |journal=[[Planetary and Space Science]] |volume=49 |issue=8 |pages=817–830 |bibcode=2001P&SS...49..817K |doi=10.1016/S0032-0633(01)00032-0}}</ref> Evidence from Tunisia indicates that marine life was deleteriously affected by a major period of increased warmth and humidity linked to a pulse of intense Deccan Traps activity,<ref>{{Cite journal |last1=Adatte |first1=Thierry |last2=Keller |first2=Gerta |last3=Stinnesbeck |first3=Wolfgang |date=28 February 2002 |title=Late Cretaceous to early Paleocene climate and sea-level fluctuations: the Tunisian record |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=178 |issue=3–4 |pages=165–196 |doi=10.1016/S0031-0182(01)00395-9 |bibcode=2002PPP...178..165A}}</ref> and that marine extinctions there began before the impact event.<ref>{{Cite journal |last=Keller |first=Gerta |date=October 1988 |title=Extinction, survivorship and evolution of planktic foraminifera across the Cretaceous/Tertiary boundary at El Kef, Tunisia |journal=Marine Micropaleontology |language=en |volume=13 |issue=3 |pages=239–263 |doi=10.1016/0377-8398(88)90005-9}}</ref> Charophyte declines in the Songliao Basin, China before the asteroid impact have been concluded to be connected to climate changes caused by Deccan Traps activity.<ref>{{Cite journal |last1=Zhang |first1=Laiming |last2=Wang |first2=Chengshan |last3=Wignall |first3=Paul B. |last4=Kluge |first4=Tobias |last5=Wan |first5=Xiaoqiao |last6=Wang |first6=Qian |last7=Gao |first7=Yuan |date=1 March 2018 |title=Deccan volcanism caused coupled pCO2 and terrestrial temperature rises, and pre-impact extinctions in northern China |journal=[[Geology (journal)|Geology]] |language=en |volume=46 |issue=3 |pages=271–274 |doi=10.1130/G39992.1 |bibcode=2018Geo....46..271Z |issn=0091-7613}}</ref>

In the years when the Deccan Traps hypothesis was linked to a slower extinction, Luis Alvarez (d. 1988) replied that paleontologists were being misled by [[Signor–Lipps effect|sparse data]]. While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. Even Walter Alvarez acknowledged that other major changes might have contributed to the extinctions.<ref>{{cite book |last=Alvarez |first=W |title=T. rex and the Crater of Doom |year=1997 |publisher=Princeton University Press |isbn=978-0-691-01630-6 |pages=[https://archive.org/details/trexcraterofdoo000alva/page/130 130]–146 |url-access=registration |url=https://archive.org/details/trexcraterofdoo000alva}}</ref> More recent arguments against the Deccan Traps as an extinction cause include that the timeline of Deccan Traps activity and pulses of climate change has been found by some studies to be asynchronous,<ref>{{Cite journal |last1=Sprain |first1=Courtney J. |last2=Renne |first2=Paul R. |last3=Vanderkluysen |first3=Loÿc |last4=Pande |first4=Kanchan |last5=Self |first5=Stephen |last6=Mittal |first6=Tushar |date=22 February 2019 |title=The eruptive tempo of Deccan volcanism in relation to the Cretaceous-Paleogene boundary |journal=[[Science (journal)|Science]] |language=en |volume=363 |issue=6429 |pages=866–870 |doi=10.1126/science.aav1446 |issn=0036-8075 |doi-access=free |pmid=30792301 |bibcode=2019Sci...363..866S }}</ref> that palynological changes do not coincide with intervals of volcanism,<ref>{{Cite journal |last1=Cripps |first1=J.A. |last2=Widdowson |first2=M. |last3=Spicer |first3=R.A. |last4=Jolley |first4=D.W. |date=1 February 2005 |title=Coastal ecosystem responses to late stage Deccan Trap volcanism: the post K–T boundary (Danian) palynofacies of Mumbai (Bombay), west India |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=216 |issue=3–4 |pages=303–332 |doi=10.1016/j.palaeo.2004.11.007 |bibcode=2005PPP...216..303C}}</ref> and that many sites show climatic stability during the latest Maastrichtian and no sign of major disruptions caused by volcanism.<ref>{{Cite journal |last1=Dzombak |first1=R.M. |last2=Sheldon |first2=N.D. |last3=Mohabey |first3=D.M. |last4=Samant |first4=B. |date=September 2020 |title=Stable climate in India during Deccan volcanism suggests limited influence on K–Pg extinction |journal=[[Gondwana Research]] |language=en |volume=85 |pages=19–31 |doi=10.1016/j.gr.2020.04.007 |doi-access=free |bibcode=2020GondR..85...19D }}</ref> Multiple modelling studies conclude that an impact event, not volcanism, fits best with available evidence of extinction patterns.<ref name=":6" /><ref name="SCI-2020017" /><ref name="NYT-20200116" />

Combining these theories, some geophysical models suggest that the impact contributed to the Deccan Traps. These models, combined with high-precision radiometric dating, suggest that the Chicxulub impact could have triggered some of the largest Deccan eruptions, as well as eruptions at active volcano sites anywhere on Earth.<ref>{{cite journal |title=State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact |last1=Renne |first1=P. R. |display-authors=etal |date=2015 |journal=[[Science (journal)|Science]] |volume=350 |issue=6256 |pages=76–78 |doi=10.1126/science.aac7549 |pmid=26430116 |bibcode=2015Sci...350...76R |doi-access=free}}</ref><ref>{{cite journal |title=Triggering of the largest Deccan eruptions by the Chicxulub impact |last1=Richards |first1=M. A. |display-authors=etal |date=2015 |journal=[[Geological Society of America Bulletin]] |doi=10.1130/B31167.1 |volume=127 |issue=11–12 |pages=1507–1520 |bibcode=2015GSAB..127.1507R |s2cid=3463018 |url=https://escholarship.org/content/qt86f3521g/qt86f3521g.pdf?t=ph1pq1 }}</ref>

=== Maastrichtian sea-level regression ===
There is clear evidence that sea levels fell in the final stage of the Cretaceous by more than at any other time in the Mesozoic era. In some Maastrichtian [[Stage (stratigraphy)|stage]] rock layers from various parts of the world, the later layers are terrestrial; earlier layers represent shorelines and the earliest layers represent seabeds. These layers do not show the tilting and distortion associated with [[Orogeny|mountain building]], therefore the likeliest explanation is a ''regression'', a drop in sea level. There is no direct evidence for the cause of the regression, but the currently accepted explanation is that the [[plate tectonics|mid-ocean ridges]] became less active and sank under their own weight.<ref name="MacLeod" /><ref>{{cite journal |title=Abrupt deep-sea warming at the end of the Cretaceous |journal=[[Geology (journal)|Geology]] |year=1998 |first1=Liangquan |last1=Li |first2=Gerta |last2=Keller |s2cid=115136793 |volume=26 |issue=11 |pages=995–998 |doi=10.1130/0091-7613(1998)026<0995:ADSWAT>2.3.CO;2 |bibcode=1998Geo....26..995L}}</ref>

A severe regression would have greatly reduced the [[continental shelf]] area, the most species-rich part of the sea, and therefore could have been enough to cause a marine mass extinction.<ref>{{Cite journal |last=Keller |first=Gerta |date=June 1989 |title=Extended Cretaceous/Tertiary boundary extinctions and delayed population change in planktonic foraminifera from Brazos River, Texas |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=4 |issue=3 |pages=287–332 |doi=10.1029/PA004i003p00287 |issn=0883-8305}}</ref><ref>{{cite book |last1=Keller |first1=Gerta |last2=Barrera |first2=Enriqueta |editor-last1=Sharpton |editor-first1=Virgil L. |editor-last2=Ward |editor-first2=Peter D. |date=1990 |title=Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality |chapter=The Cretaceous/Tertiary boundary impact hypothesis and the paleontological record |publisher=Geological Society of America |doi=10.1130/SPE247-p563 |isbn=9780813722474}}</ref> This change would not have caused the extinction of the ammonites. The regression would also have caused climate changes, partly by disrupting winds and ocean currents and partly by reducing the Earth's [[albedo]] and increasing global temperatures.<ref name="Marshall" /> Marine regression also resulted in the loss of [[Inland sea (geology)|epeiric seas]], such as the [[Western Interior Seaway]] of North America. The loss of these seas greatly altered habitats, removing [[coastal plain]]s that ten million years before had been host to diverse communities such as are found in rocks of the Dinosaur Park Formation. Another consequence was an expansion of [[Fresh water|freshwater]] environments, since continental runoff now had longer distances to travel before reaching [[ocean]]s. While this change was favorable to freshwater [[vertebrate]]s, those that prefer marine environments, such as sharks, suffered.<ref name="AF04" />

However, sea level fall as a cause of the extinction event is contradicted by other evidence, namely that sections which show no sign of marine regression still show evidence of a major drop in diversity.<ref>{{Cite journal |last1=Jiang |first1=M. J. |last2=Gartner |first2=S. |date=1986 |title=Calcareous Nannofossil Succession across the Cretaceous/Tertiary Boundary in East-Central Texas |journal=Micropaleontology |volume=32 |issue=3 |pages=232 |doi=10.2307/1485619 |jstor=1485619}}</ref>

=== Multiple causes ===
Proponents of multiple causation view the suggested single causes as either too small to produce the vast scale of the extinction, or not likely to produce its observed taxonomic pattern. In a review article, J. David Archibald and David E. Fastovsky discussed a scenario combining three major postulated causes: volcanism, [[marine regression]], and extraterrestrial impact. In this scenario, terrestrial and marine communities were stressed by the changes in, and loss of, habitats. Dinosaurs, as the largest vertebrates, were the first affected by environmental changes, and their diversity declined. At the same time, [[Particle|particulate]] materials from volcanism cooled and dried areas of the globe. Then an impact event occurred, causing collapses in photosynthesis-based food chains, both in the already-stressed terrestrial food chains and in the marine food chains.<ref name="AF04" />

Based on studies at [[Seymour Island]] in [[Antarctica]], Sierra Petersen and colleagues argue that there were two separate extinction events near the Cretaceous–Paleogene boundary, with one correlating to Deccan Trap volcanism and one correlated with the Chicxulub impact. The team analyzed combined extinction patterns using a new clumped isotope temperature record from a hiatus-free, expanded K–Pg boundary section. They documented a 7.8±3.3&nbsp;°C warming synchronous with the onset of Deccan Traps volcanism and a second, smaller warming at the time of meteorite impact. They suggested that local warming had been amplified due to the simultaneous disappearance of continental or sea ice. Intra-shell variability indicates a possible reduction in seasonality after Deccan eruptions began, continuing through the meteorite event. Species extinction at Seymour Island occurred in two pulses that coincide with the two observed warming events, directly linking the end-Cretaceous extinction at this site to both volcanic and meteorite events via climate change.<ref name="Petersen, Sierra V. 2016">{{cite journal |last1=Petersen |first1=Sierra V. |last2=Dutton |first2=Andrea |last3=Lohmann |first3=Kyger C. |year=2016 |title=End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change |journal=[[Nature Communications]] |volume=7 |page=12079 |bibcode=2016NatCo...712079P |doi=10.1038/ncomms12079 |pmc=4935969 |pmid=27377632}}</ref>
[[File: Thescelosaurus after K-Pg.png|thumb|right|Speculative artist's rendering of a ''[[Thescelosaurus]]'' shortly after the K-Pg event]]

== See also ==
* {{Annotated link|Climate across Cretaceous–Paleogene boundary}}
* {{Annotated link|Late Devonian extinction}}
* {{Annotated link|List of possible impact structures on Earth}}
* {{Annotated link|Late Ordovician mass extinction}}
* {{Annotated link|Permian–Triassic extinction event}}
* {{Annotated link|Timeline of Cretaceous–Paleogene extinction event research}}
* {{Annotated link|Triassic–Jurassic extinction event}}

== Explanatory notes ==
{{notelist|1}}

== Citations ==
{{reflist}}

== Further reading ==

{{refbegin}}
* {{Cite web |author=Cowen, R. |year=2000 |title=The K–T extinction |url=http://www.ucmp.berkeley.edu/education/events/cowen1b.html |publisher=[[University of California Museum of Paleontology]] |access-date=2007-08-02}}
* {{Cite journal |last1=DePalma |first1=Robert A. |display-authors=etal |title=A seismically induced onshore surge deposit at the KPg boundary, North Dakota |journal=PNAS |volume=116 |issue=17 |pages=8190–8199 |date=1 April 2019 |doi=10.1073/pnas.1817407116 |doi-access=free |bibcode=2019PNAS..116.8190D |pmid=30936306 |pmc=6486721}}
* {{Cite book |last=Fortey |first=Richard |author-link=Richard Fortey |year=2005 |title=Earth: An Intimate History |url=https://books.google.com/books?id=8i8UzOYJlgUC |location=New York |publisher=Vintage Books |isbn=978-0-375-70620-2 |oclc=54537112}}
* [https://gsa.confex.com/gsa/2017AM/webprogram/Session43180.html Papers and presentations resulting from the 2016 Chicxulub drilling project]—The [[Geological Society of America]], GSA Annual Meeting in Seattle, Washington, USA – 2017, Session No. 192
* {{Cite web |author=Kring, D.A. |year=2005 |title=Chicxulub impact event: Understanding the K–T boundary |publisher=NASA Space Imagery Center |url=http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Chicx_title.html |access-date=2007-08-02 |archive-url=https://web.archive.org/web/20070629230804/http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Chicx_title.html |archive-date=29 June 2007}}
* {{Cite magazine |last=Preston |first=Douglas |author-link=Douglas Preston |date=8 April 2019 |title=The Day the Dinosaurs Died |url=https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died |magazine=[[The New Yorker]] |pages=52–65 |quote=Robert A. de&nbsp;Palm has found strong evidence that the [[dinosaur]]s—and nearly all other life on [[Earth]]—were indeed wiped out 66&nbsp;million years ago by the [[Chicxulub asteroid]]}} 
{{refend}}

== External links ==
{{Commons category|K/T Event}}
* [http://www.ucmp.berkeley.edu/diapsids/extinction.html What killed the dinosaurs?]—University of California Museum of Paleontology (1995)
* [http://www.geolsoc.org.uk/chicxulub The Great Chicxulub Debate 2004]—[[Geological Society of London]]

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{{DEFAULTSORT:Cretaceous-Tertiary Extinction Event}}
[[Category:Late Cretaceous extinctions| ]]
[[Category:Cretaceous–Paleogene boundary|*]]
[[Category:Paleogene extinctions|*]]
[[Category:Cenozoic volcanism]]
[[Category:Events in the geological history of Earth]]
[[Category:Events that forced the climate]]
[[Category:Evolution of mammals]]
[[Category:Hypothetical impact events]]
[[Category:Megatsunamis]]
[[Category:Mesozoic volcanism]]
[[Category:Meteorological hypotheses]]
[[Category:Dinosaurs]]