Editing Cretaceous

{{Short description|Third and last period of the Mesozoic Era}}
{{Infobox geologic timespan
| name                         = Cretaceous
| color                        = Cretaceous
| top_bar                      = Phanerozoic
| time_start                   = 143.1
| time_start_prefix            = c.&nbsp;
| time_end                     = 66.0
| image_map                    = Mollweide Paleographic Map of Earth, 105 Ma (Albian Age).png 
| caption_map                  = A map of Earth as it appeared 105 million years ago during the Early Cretaceous period
| image_outcrop                =
| caption_outcrop              =
| image_art                    =
| caption_art                  =
<!--Chronology-->  
| timeline                     = Cretaceous
<!--Etymology-->
| name_formality               = Formal
| name_accept_date             =
| alternate_spellings          =
| synonym1                     =
| synonym1_coined              =
| synonym2                     =
| synonym2_coined              =
| synonym3                     =
| synonym3_coined              =
| nicknames                    =
| former_names                 =
| proposed_names               =
<!--Usage Information--> 
| celestial_body               = Earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
| formerly_used_by             =
| not_used_by                  =
<!--Definition-->
| chrono_unit                  = Period
| strat_unit                   = System
| proposed_by                  = 
| timespan_formality           = Formal
| lower_boundary_def           = Not formally defined
| lower_def_candidates         =
* Magnetic—base of [[Chronozone|Chron]] M18r
* Base of [[Calpionellid]] zone B
* [[First appearance datum|FAD]] of [[Ammonite]] ''[[Berriasella jacobi]]''
| lower_gssp_candidates        = None
| upper_boundary_def           = [[Iridium]]-enriched layer associated with a major meteorite impact and subsequent [[K-Pg extinction event]]
| upper_gssp_location          = El Kef Section, [[El Kef]], [[Tunisia]]
| upper_gssp_coords            = {{Coord|36.1537|N|8.6486|E|display=inline}}
| upper_gssp_accept_date       = 1991
<!--Atmospheric and Climatic Data-->
| sea_level                    =
}}

The '''Cretaceous''' ({{IPAc-en|ipa|k|r|ɪ|ˈ|t|eɪ|ʃ|ə|s}} {{Respell|krih|TAY|shəss}})<ref>{{Dictionary.com|Cretaceous}}</ref> is a [[geological period]] that lasted from about 143.1 to 66 [[mya (unit)|million years ago]] (Mya). It is the third and final period of the [[Mesozoic]] [[Era (geology)|Era]], as well as the longest. At around 77.1 million years, it is the ninth and longest geological period of the entire [[Phanerozoic]]. The name is derived from the Latin {{lang|la|[[wikt:creta#Latin|creta]]}}, '[[chalk]]', which is abundant in the latter half of the period. It is usually abbreviated '''K''', for its German translation {{lang|de|Kreide}}.

The Cretaceous was a period with a relatively warm [[climate]], resulting in high [[Sea level#Local and eustatic|eustatic sea levels]] that created numerous shallow [[Inland sea (geology)|inland seas]]. These oceans and seas were populated with now-[[extinct]] [[marine reptile]]s, [[ammonites]], and [[rudists]], while [[dinosaur]]s continued to dominate on land. The world was largely ice-free, although there is some evidence of brief periods of glaciation during the cooler first half, and forests extended to the poles.

Many of the dominant taxonomic groups present in modern times can be ultimately traced back to origins in the Cretaceous. During this time, new groups of [[mammal]]s and [[birds]] appeared, including the earliest relatives of [[Placentalia|placentals]] and [[marsupial]]s ([[Eutheria]] and [[Metatheria]] respectively), with the earliest [[crown group]] birds appearing towards to the end of the Cretaceous. [[Teleost]] fish, the most diverse group of modern vertebrates continued to diversify during the Cretaceous with the appearance of their most diverse subgroup [[Acanthomorpha]] during this period. During the Early Cretaceous, [[flowering plant]]s appeared and began to rapidly diversify, becoming the dominant group of [[plant]]s across the Earth by the end of the Cretaceous, coincident with the decline and [[extinction]] of previously widespread [[gymnosperm]] groups.

The Cretaceous (along with the Mesozoic) ended with the [[Cretaceous–Paleogene extinction event]], a large [[Extinction event|mass extinction]] in which many groups, including non-avian dinosaurs, [[pterosaur]]s, and large [[marine reptile]]s, died out, widely thought to have been caused by the impact of a large asteroid that formed the [[Chicxulub crater]] in the Gulf of Mexico. The end of the Cretaceous is defined by the abrupt [[Cretaceous–Paleogene boundary]] (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and [[Cenozoic]] [[era (geology)|Eras]].

==Etymology and history==
The Cretaceous as a separate period was first defined by Belgian geologist [[Jean Baptiste Julien d'Omalius d'Halloy|Jean d'Omalius d'Halloy]] in 1822 as the ''Terrain Crétacé'',<ref>{{cite journal | author = d’Halloy, d’O., J.-J. | year = 1822 | title = Observations sur un essai de carte géologique de la France, des Pays-Bas, et des contrées voisines |trans-title=Observations on a trial geological map of France, the Low Countries, and neighboring countries | journal = Annales des Mines | volume = 7 | pages = 353–376 | url = https://books.google.com/books?id=c-ocAQAAIAAJ&pg=PA353}}  From page 373:  "La troisième, qui correspond à ce qu'on a déja appelé formation de la craie, sera désigné par le nom de terrain crétacé." (The third, which corresponds to what was already called the "chalk formation", will be designated by the name "chalky terrain".)</ref> using [[stratum|strata]] in the [[Paris Basin]]<ref>{{cite book |trans-title=Great Soviet Encyclopedia |title=Sovetskaya Enciklopediya  |publisher=Sovetskaya Enciklopediya |edition=3rd |pages=vol. 16, p. 50 |year=1974 |location=Moscow |language=ru |no-pp=true |title-link=Great Soviet Encyclopedia}}</ref> and named for the extensive beds of [[chalk]] ([[calcium carbonate]] deposited by the shells of marine [[invertebrate]]s, principally [[coccoliths]]), found in the upper Cretaceous of [[Western Europe]]. The name Cretaceous was derived from the [[Latin]] ''creta'', meaning ''chalk''.<ref>{{cite book|title=Glossary of Geology|publisher=American Geological Institute|edition=3rd|page= 165|year=1972|location=Washington, D.C.}}</ref> The twofold division of the Cretaceous was implemented by [[William Conybeare (geologist)|Conybeare]] and Phillips in 1822. [[Alcide d'Orbigny]] in 1840 divided the French Cretaceous into five ''étages'' (stages): the [[Neocomian]], Aptian, Albian, Turonian, and Senonian, later adding the ''Urgonian'' between Neocomian and Aptian and the Cenomanian between the Albian and Turonian.<ref>{{Citation|last1=Ogg|first1=J.G.|title=Cretaceous|date=2012|url=https://linkinghub.elsevier.com/retrieve/pii/B9780444594259000275|work=The Geologic Time Scale|pages=793–853|publisher=Elsevier|language=en|doi=10.1016/b978-0-444-59425-9.00027-5|isbn=978-0-444-59425-9|access-date=2021-01-08|last2=Hinnov|first2=L.A.|last3=Huang|first3=C.}}</ref>

==Geology==

===Subdivisions===

The Cretaceous is divided into [[Early Cretaceous|Early]] and [[Late Cretaceous]] [[epoch (geology)|epochs]], or Lower and Upper Cretaceous [[series (stratigraphy)|series]]. In older literature, the Cretaceous is sometimes divided into three series: [[Neocomian]] (lower/early), [[Gallic epoch|Gallic]] (middle) and [[Senonian]] (upper/late). A subdivision into 12 [[stage (stratigraphy)|stages]], all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use.

From youngest to oldest, the subdivisions of the Cretaceous period are:<ref>Cohen, K.M., Finney, S.C., Gibbard, P.L. & Fan, J.-X. (2013; updated) [https://stratigraphy.org/ICSchart/ChronostratChart2024-12.pdf The ICS International Chronostratigraphic Chart]. Episodes 36: 199–204.</ref>

{| class="wikitable"
|+Subdivisions of the Cretaceous
|-
! rowspan=2|Epoch !! rowspan=2|Age/Stage !! Start<br>''(base)'' !! rowspan="2" |Definition !!rowspan=2|Etymology
|-
! align="center" |([[Megaannum|Mya]])
|-
|[[Paleocene]]
|[[Danian]]
|66
|
|
|-
| rowspan="6" style="background-color: {{period color|late cretaceous}};" | [[Late Cretaceous]]|| style="background-color: {{period color|maastrichtian}};" | [[Maastrichtian]]|| align="center" | 72.2 ± 0.2 || top: iridium anomaly at the [[Cretaceous–Paleogene boundary]]<br>base:first occurrence of ''[[Pachydiscus|Pachydiscus neubergicus]]''
| [[Maastricht Formation]], [[Maastricht]], Netherlands
|-
| style="background-color: {{period color|campanian}};" | [[Campanian]]|| align="center" | 83.6 ± 0.2 || base: last occurrence of ''[[Marsupites|Marsupites testudinarius]]''|| [[Champagne (province)|Champagne]], France
|-
| style="background-color: {{period color|santonian}};" | [[Santonian]]|| align="center" | 85.7 ± 0.2 || base: first occurrence of ''[[Cladoceramus|Cladoceramus undulatoplicatus]]''|| [[Saintes, Charente-Maritime|Saintes]], France
|-
| style="background-color: {{period color|coniacian}};" | [[Coniacian]]|| align="center" | 89.8 ± 0.3 || base: first occurrence of ''[[Cremnoceramus|Cremnoceramus rotundatus]]''|| [[Cognac, France|Cognac]], France
|-
| style="background-color: {{period color|turonian}};" | [[Turonian]]|| align="center" | 93.9 ± 0.2 || base: first occurrence of ''[[Watinoceras|Watinoceras devonense]]''|| [[Tours]], France
|-
| style="background-color: {{period color|cenomanian}};" | [[Cenomanian]]|| align="center" | 100.5 ± 0.1 || base: first occurrence of ''[[Rotalipora|Rotalipora globotruncanoides]]''|| ''Cenomanum''; [[Le Mans]], France
|-
| rowspan="6" style="background-color: {{period color|early cretaceous}};" | [[Early Cretaceous]]|| style="background-color: {{period color|albian}};" | [[Albian]]|| align="center" | 113.2 ± 0.3 || base: first occurrence of ''[[Praediscosphaera|Praediscosphaera columnata]]''|| [[Aube (river)|Aube]], France
|-
| style="background-color: {{period color|aptian}};" | [[Aptian]]|| align="center" | 121.4 ± 0.6 || base: [[magnetic anomaly]] M0r || [[Apt, Vaucluse|Apt]], France
|-
| style="background-color: {{period color|barremian}};" | [[Barremian]]|| align="center" | 125.77 ± 1.5 || base: first occurrence of ''[[Spitidiscus|Spitidiscus hugii]]'' and ''S. vandeckii''|| [[Barrême]], France
|-
| style="background-color: {{period color|hauterivian}};" | [[Hauterivian]]|| align="center" | 132.6 ± 0.6 || base: first occurrence of ''[[Acanthodiscus]]''|| [[Hauterive, Neuchâtel|Hauterive]], Switzerland
|-
| style="background-color: {{period color|valanginian}};" | [[Valanginian]]|| align="center" | 137.05 ± 0.2 || base: first occurrence of ''[[Calpionellites|Calpionellites darderi]]''|| [[Valangin]], Switzerland
|-
| style="background-color: {{period color|berriasian}};" | [[Berriasian]] || align="center" | 143.1 ±0.6 || base: first occurrence of ''[[Berriasella|Berriasella jacobi]]'' (traditionally);<br>first occurrence of ''[[Calpionella|Calpionella alpina]]'' (since 2016) || [[Berrias-et-Casteljau|Berrias]], France
|-
|}

===Boundaries===
[[File:Impact event.jpg|thumb|The impact of a [[meteorite]] or [[comet]] is today widely accepted as the main reason for the [[Cretaceous–Paleogene extinction event]].]]
{{see also|Cretaceous–Paleogene extinction event}}
The lower boundary of the Cretaceous is currently undefined, and the Jurassic–Cretaceous boundary is currently the only system boundary to lack a defined [[Global Boundary Stratotype Section and Point]] (GSSP). Placing a GSSP for this boundary has been difficult because of the strong regionality of most biostratigraphic markers, and the lack of any [[Chemostratigraphy|chemostratigraphic]] events, such as [[isotope]] excursions (large sudden changes in [[Stable isotope ratio|ratios of isotopes]]) that could be used to define or correlate a boundary. [[Calpionellid]]s, an enigmatic group of [[plankton]]ic [[protist]]s with urn-shaped calcitic [[Test (biology)|tests]] briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested as the most promising candidates for fixing the Jurassic–Cretaceous boundary.<ref>{{Cite journal|last=WIMBLEDON|first=William A.P.|date=2017-12-27|title=Developments with fixing a Tithonian/Berriasian (J/K) boundary|url=https://www.researchgate.net/publication/321670503|journal=Volumina Jurassica|volume=15|issue=1|pages=107–112|doi=10.5604/01.3001.0010.7467|doi-broken-date=23 May 2025 |issn=1731-3708}}</ref> In particular, the first appearance ''[[Calpionella|Calpionella alpina]]'', coinciding with the base of the eponymous Alpina subzone, has been proposed as the definition of the base of the Cretaceous.<ref>{{Cite journal|last1=Wimbledon|first1=William A.P.|last2=Rehakova|first2=Daniela|last3=Svobodová|first3=Andrea|last4=Schnabl|first4=Petr|last5=Pruner|first5=Petr|last6=Elbra|first6=Tiiu|last7=Šifnerová|first7=Kristýna|last8=Kdýr|first8=Šimon|last9=Frau|first9=Camille|last10=Schnyder|first10=Johann|last11=Galbrun|first11=Bruno|date=2020-02-11|title=Fixing a J/K boundary: A comparative account of key Tithonian–Berriasian profiles in the departments of Drôme and Hautes-Alpes, France|url=https://www.sav.sk/index.php?lang=sk&doc=journal-list&part=article_response_page&journal_article_no=18100|journal=[[Geologica Carpathica]]|volume=71|issue=1|doi=10.31577/GeolCarp.71.1.3|doi-access=free|bibcode=2020GCarp..71..1.3W }}</ref> The working definition for the boundary has often been placed as the first appearance of the ammonite ''[[Strambergella jacobi]]'', formerly placed in the genus ''[[Berriasella]]'', but its use as a stratigraphic indicator has been questioned, as its first appearance does not correlate with that of ''C. alpina''.<ref>{{Cite journal|last1=Frau|first1=Camille|last2=Bulot|first2=Luc G.|last3=Reháková|first3=Daniela|last4=Wimbledon|first4=William A.P.|last5=Ifrim|first5=Christina|date=November 2016|title=Revision of the ammonite index species Berriasella jacobi Mazenot, 1939 and its consequences for the biostratigraphy of the Berriasian Stage|url=http://linkinghub.elsevier.com/retrieve/pii/S0195667116301057|journal=[[Cretaceous Research]]|language=en|volume=66|pages=94–114|doi=10.1016/j.cretres.2016.05.007|bibcode=2016CrRes..66...94F }}</ref> The boundary is officially considered by the [[International Commission on Stratigraphy]] to be approximately 145 million years ago,<ref>Cohen, K.M., Finney, S.C., Gibbard, P.L. & Fan, J.-X. (2013; updated) [https://stratigraphy.org/ICSchart/ChronostratChart2020-03.pdf The ICS International Chronostratigraphic Chart]. Episodes 36: 199–204.</ref> but other estimates have been proposed based on U-Pb geochronology, ranging as young as 140 million years ago.<ref>{{Cite journal|last1=Lena|first1=Luis|last2=López-Martínez|first2=Rafael|last3=Lescano|first3=Marina|last4=Aguire-Urreta|first4=Beatriz|last5=Concheyro|first5=Andrea|last6=Vennari|first6=Verónica|last7=Naipauer|first7=Maximiliano|last8=Samankassou|first8=Elias|last9=Pimentel|first9=Márcio|last10=Ramos|first10=Victor A.|last11=Schaltegger|first11=Urs|date=2019-01-08|title=High-precision U–Pb ages in the early Tithonian to early Berriasian and implications for the numerical age of the Jurassic–Cretaceous boundary|journal=Solid Earth|volume=10|issue=1|pages=1–14|doi=10.5194/se-10-1-2019|bibcode=2019SolE...10....1L|s2cid=135382485|issn=1869-9529|doi-access=free|hdl=11336/97384|hdl-access=free}}</ref><ref>{{cite journal |last1=Vennari |first1=Verónica V. |last2=Lescano |first2=Marina |last3=Naipauer |first3=Maximiliano |last4=Aguirre-Urreta |first4=Beatriz |last5=Concheyro |first5=Andrea|last6=Schaltegger |first6=Urs |last7=Armstrong |first7=Richard |last8=Pimentel |first8=Marcio |last9=Ramos |first9=Victor A. |author-link9=Víctor Alberto Ramos |date=2014 |title=New constraints on the Jurassic–Cretaceous boundary in the High Andes using high-precision U–Pb data |journal=[[Gondwana Research]] |volume=26 |issue= 1|pages=374–385 |doi= 10.1016/j.gr.2013.07.005|bibcode=2014GondR..26..374V |hdl=11336/30971 |hdl-access=free }}</ref>

The upper boundary of the Cretaceous is sharply defined, being placed at an [[iridium]]-rich layer found worldwide that is believed to be associated with the [[Chicxulub Crater|Chicxulub impact crater]], with its boundaries circumscribing parts of the [[Yucatán Peninsula]] and extending into the [[Gulf of Mexico]]. This layer has been dated at 66.043 Mya.<ref>{{cite journal|author=Renne, Paul R.|display-authors=etal|year=2013|title=Time scales of critical events around the Cretaceous-Paleogene boundary|journal=[[Science (journal)|Science]]|volume=339|issue=6120|pages=684–688|bibcode=2013Sci...339..684R|doi=10.1126/science.1230492|pmid=23393261|s2cid=6112274}}</ref>

At the end of the Cretaceous, the impact of a large [[Small Solar System body|body]] with the Earth may have been the punctuation mark at the end of a progressive decline in [[biodiversity]] during the Maastrichtian age. The result was the extinction of three-quarters of Earth's plant and animal species. The impact created the sharp break known as the [[K–Pg boundary]] (formerly known as the K–T boundary). Earth's biodiversity required substantial time to recover from this event, despite the probable existence of an abundance of vacant [[ecological niche]]s.<ref name="MacLeod">{{cite journal | url=https://www.researchgate.net/publication/39065961 | title=The Cretaceous–Tertiary biotic transition |author1=MacLeod, N |author2=Rawson, PF |author3=Forey, PL |author4=Banner, FT |author5=Boudagher-Fadel, MK |author6=Bown, PR |author7=Burnett, JA |author8=Chambers, P |author9=Culver, S |author10=Evans, SE |author11=Jeffery, C |author12=Kaminski, MA |author13=Lord, AR |author14=Milner, AC |author15=Milner, AR |author16=Morris, N |author17=Owen, E |author18=Rosen, BR  |author19=Smith, AB |author20=Taylor, PD |author21=Urquhart, E |author22=Young, JR |display-authors=7 | journal=[[Journal of the Geological Society]] | year=1997 | volume=154 | issue=2 | pages=265–292 | doi=10.1144/gsjgs.154.2.0265| bibcode=1997JGSoc.154..265M | s2cid=129654916 }}</ref>

Despite the severity of the K-Pg extinction event, there were significant variations in the rate of extinction between and within different [[clade]]s. Species that depended on [[photosynthesis]] declined or became extinct as atmospheric particles blocked [[solar energy]]. As is the case today, photosynthesizing organisms, such as [[phytoplankton]] and land [[plant]]s, formed the primary part of the [[food chain]] in the late Cretaceous, and all else that depended on them suffered, as well. [[Herbivore|Herbivorous]] animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, the top [[predator]]s, such as ''[[Tyrannosaurus|Tyrannosaurus rex]]'', also perished.<ref>{{cite journal|author1=Wilf, P  |author2=Johnson KR|title=Land plant extinction at the end of the Cretaceous: a quantitative analysis of the North Dakota megafloral record|journal=[[Paleobiology (journal)|Paleobiology]]|year=2004|volume=30|issue=3|pages=347–368|doi = 10.1666/0094-8373(2004)030<0347:LPEATE>2.0.CO;2|bibcode=2004Pbio...30..347W |s2cid=33880578 }}</ref> Yet only three major groups of [[tetrapod]]s disappeared completely; the non-avian [[dinosaur]]s, the [[Plesiosauria|plesiosaurs]] and the [[pterosaur]]s. The other Cretaceous groups that did not survive into the Cenozoic {{nowrap|Era{{tsp}}{{mdash}}}}{{tsp}}the [[ichthyosaur]]s, last remaining [[Temnospondyli|temnospondyls]] ([[Koolasuchus]]), and nonmammalian {{nowrap|[[cynodont]]s ([[Tritylodontidae]]) {{tsp}}{{mdash}}}}{{tsp}} were already extinct millions of years before the event occurred.{{Citation needed|date=April 2017}}

[[Coccolithophorids]] and [[mollusc]]s, including [[ammonite]]s, [[rudist]]s, [[freshwater snail]]s, and [[mussel]]s, as well as organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, [[Ammonoidea|ammonites]] are thought to have been the principal food of [[mosasaur]]s, a group of giant marine [[lizard]]s related to snakes that became extinct at the boundary.<ref name="Kauffman">{{cite journal| last =Kauffman| first =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| year =2004| doi = 10.1669/0883-1351(2004)019<0096:MPOUCN>2.0.CO;2| bibcode=2004Palai..19...96K| s2cid =130690035| url =http://doc.rero.ch/record/14992/files/PAL_E2143.pdf}}</ref>

[[Omnivores]], [[insectivores]], and [[carrion]]-eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous, there seem to have been no purely herbivorous or [[carnivore|carnivorous]] [[mammal]]s. Mammals and birds that survived the extinction fed on [[insect]]s, [[larva]]e, [[worm]]s, and snails, which in turn fed on dead plant and animal matter. Scientists theorise that these organisms survived the collapse of plant-based food chains because they fed on [[Detritus (biology)|detritus]].<ref name="SheehanHansen">{{cite journal|author1=Shehan, P  |author2=Hansen, TA | 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| year =1986| doi =10.1130/0091-7613(1986)14<868:DFAABT>2.0.CO;2|bibcode = 1986Geo....14..868S }}</ref><ref name="MacLeod"/><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, RA |author5= Medina, FA |name-list-style=amp |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]], few groups of animals became extinct. Stream communities rely less on food from living plants and more on detritus that washes in from land. This particular ecological niche buffered them from extinction.<ref>{{cite journal|title=Major extinctions of land-dwelling vertebrates at the Cretaceous–Paleogene boundary, eastern Montana|author1=Sheehan, PM  |author2=Fastovsky, DE|year=1992|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> 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 seafloor. Animals in the water column are almost entirely dependent on [[primary production]] from living phytoplankton, while animals living on or in the [[ocean floor]] feed on detritus or can switch to detritus feeding.<ref name="MacLeod"/>

The largest air-breathing survivors of the event, [[crocodilian]]s and [[Choristodera|champsosaurs]], were semiaquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food and go into hibernation when conditions are unfavorable, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.<ref name="SheehanHansen"/>

=== Geologic formations ===
[[File:MosasaurusHoffmann.jpg|thumb|left|Drawing of fossil jaws of ''[[Mosasaurus|Mosasaurus hoffmanni]]'', from the [[Maastrichtian]] of [[Limburg (Netherlands)|Dutch Limburg]], by Dutch geologist [[Pieter Harting]] (1866)]]
[[File:9119 - Milano, Museo storia naturale - Scipionyx samniticus - Foto Giovanni Dall'Orto 22-Apr-2007.jpg|thumb|''[[Scipionyx]]'', a [[theropod]] dinosaur from the Early Cretaceous of Italy]]
The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms. The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of [[Lake sediment|marine]] [[limestone]], a rock type that is formed under warm, shallow marine conditions. Due to the high sea level, there was extensive [[Accommodation (geology)|space]] for such [[sedimentation]]. Because of the relatively young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide.

[[Chalk]] is a rock type characteristic for (but not restricted to) the Cretaceous. It consists of [[coccolith]]s, microscopically small [[calcite]] skeletons of [[coccolithophore]]s, a type of [[algae]] that prospered in the Cretaceous seas.

Stagnation of deep-sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half of the world's petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic [[shale]]s were formed during this interval,{{sfn|Stanley|1999| pp=481–482}} such as the [[Mancos Shale]] of western North America.<ref>{{cite journal |last1=Weimar |first1=R.J. |title=Upper Cretaceous Stratigraphy, Rocky Mountain Area |journal=AAPG Bulletin |date=1960 |volume=44 |pages=1–20 |doi=10.1306/0BDA5F6F-16BD-11D7-8645000102C1865D}}</ref> These shales are an important [[source rock]] for [[Fossil fuel|oil and gas]], for example in the subsurface of the North Sea.

==== Europe ====
{{see also|:Category:Cretaceous System of Europe}}
In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the [[Chalk Group]], which forms the [[white cliffs of Dover]] on the south coast of [[England]] and similar cliffs on the [[France|French]] [[Normandy|Normandian]] coast. The [[group (stratigraphy)|group]] is found in England, northern France, the [[Low Countries]], northern [[Germany]], [[Denmark]] and in the subsurface of the southern part of the [[North Sea]]. Chalk is not easily [[Consolidation (soil)|consolidated]] and the Chalk Group still consists of loose sediments in many places. The group also has other [[limestone]]s and [[arenite]]s. Among the fossils it contains are [[sea urchin]]s, [[belemnite]]s, [[ammonite]]s and sea reptiles such as ''[[Mosasaurus]]''.

In southern Europe, the Cretaceous is usually a marine system consisting of [[Competence (geology)|competent]] limestone beds or incompetent [[marl]]s. Because the [[Alpine orogeny|Alpine mountain chains]] did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European [[continental shelf]], at the margin of the [[Tethys Ocean]].

==== North America ====
{{see also|:Category:Cretaceous System of North America}}
[[File:Map of North America with the Western Interior Seaway during the Campanian (Upper Cretaceous).png|thumb|Map of North America During the Late Cretaceous]]
During the Cretaceous, the present North American continent was isolated from the other continents. In the Jurassic, the North Atlantic already opened, leaving a proto-ocean between Europe and North America. From north to south across the continent, the [[Western Interior Seaway]] started forming. This inland sea separated the elevated areas of [[Laramidia]] in the west and [[Appalachia (landmass)|Appalachia]] in the east. Three dinosaur clades found in Laramidia (troodontids, therizinosaurids and oviraptorosaurs) are absent from Appalachia from the Coniacian through the Maastrichtian.<ref name=Brownstein2018>{{cite journal |last=Brownstein |first=Chase D |year=2018 |title=The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia |url=https://palaeo-electronica.org/content/2018/2123-appalachia-biogeography |journal=[[Palaeontologia Electronica]] |volume=21 |pages=1–56 |doi=10.26879/801|doi-access=free }}</ref>

== Paleogeography ==
During the Cretaceous, the late-[[Paleozoic]]-to-early-Mesozoic [[supercontinent]] of [[Pangaea]] completed its [[Plate tectonics|tectonic]] breakup into the present-day [[continent]]s, although their positions were substantially different at the time. As the [[Atlantic Ocean]] widened, the convergent-margin mountain building ([[orogeny|orogenies]]) that had begun during the [[Jurassic]] continued in the [[American cordillera|North American Cordillera]], as the [[Nevadan orogeny]] was followed by the [[Sevier orogeny|Sevier]] and [[Laramide orogeny|Laramide orogenies]].

[[Gondwana]] had begun to break up during the Jurassic Period, but its fragmentation accelerated during the Cretaceous and was largely complete by the end of the period. [[South America]], [[Antarctica]], and [[Australia]] rifted away from [[Africa]] (though [[India]] and [[Madagascar]] remained attached to each other until around 80 million years ago); thus, the South Atlantic and [[Indian Ocean]]s were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising [[Sea level#Dry land|eustatic sea levels]] worldwide. To the north of Africa the [[Tethys Sea]] continued to narrow. During most of the Late Cretaceous, North America would be divided in two by the [[Western Interior Seaway]], a large interior sea, separating [[Laramidia]] to the west and [[Appalachia (landmass)|Appalachia]] to the east, then receded late in the period, leaving thick marine deposits sandwiched between [[coal]] beds. Bivalve palaeobiogeography also indicates that Africa was split in half by a shallow sea during the Coniacian and Santonian, connecting the Tethys with the South Atlantic by way of the central Sahara and Central Africa, which were then underwater.<ref>{{cite journal |last1=Moussavou |first1=Benjamin Musavu |date=25 September 2015 |title=Bivalves (Mollusca) from the Coniacian-Santonian Anguille Formation from Cap Esterias, Northern Gabon, with notes on paleoecology and paleobiogeography |url=https://bioone.org/journals/geodiversitas/volume-37/issue-3/g2015n3a2/Bivalves-Mollusca-from-the-Coniacian-Santonian-Anguille-Formation-from-Cap/10.5252/g2015n3a2.short |journal=Geodiversitas |volume=37 |issue=3 |pages=315–324 |doi=10.5252/g2015n3a2 |bibcode=2015Geodv..37..315M |s2cid=128803778 |access-date=28 December 2022}}</ref> Yet another shallow seaway ran between what is now Norway and Greenland, connecting the Tethys to the Arctic Ocean and enabling biotic exchange between the two oceans.<ref>{{cite journal |last1=Mutterlose |first1=Jörg |last2=Brumsack |first2=Hans |last3=Flögel |first3=Sascha |last4=Hay |first4=William |last5=Klein |first5=Christian |last6=Langrock |first6=Uwe |last7=Lipinski |first7=Marcus |last8=Ricken |first8=Werner |last9=Söding |first9=Emanuel |last10=Stein |first10=Rüdiger |last11=Swientek |first11=Oliver |date=26 February 2003 |title=The Greenland-Norwegian Seaway: A key area for understanding Late Jurassic to Early Cretaceous paleoenvironments |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001pa000625 |journal=[[Paleoceanography and Paleoclimatology]] |volume=18 |issue=1 |pages=10-1-10-25 |doi=10.1029/2001pa000625 |bibcode=2003PalOc..18.1010M |access-date=14 May 2023}}</ref> At the peak of the Cretaceous [[transgression (geology)|transgression]], one-third of Earth's present land area was submerged.<ref>{{cite book |first1=Dougal |last1=Dixon |first2=M J |last2=Benton |first3=Ayala |last3=Kingsley |first4=Julian |last4=Baker|title=Atlas of Life on Earth |location=New York |publisher=Barnes & Noble Books |year=2001 |page=215 |isbn=9780760719572}}</ref>

The Cretaceous is justly famous for its [[chalk]]; indeed, more chalk formed in the Cretaceous than in any other period in the [[Phanerozoic]].{{sfn|Stanley|1999|p=280}} [[Mid-ocean ridge]] activity—or rather, the circulation of seawater through the enlarged ridges—enriched the oceans in [[calcium]]; this made the oceans more saturated, as well as increased the [[bioavailability]] of the element for [[Coccolithophores|calcareous nanoplankton]].{{sfn|Stanley|1999|pp=279–281}} These widespread [[carbonate]]s and other [[sedimentary rock|sedimentary deposits]] make the Cretaceous rock record especially fine. Famous [[Geologic formation|formations]] from North America include the rich marine fossils of [[Kansas]]'s [[Smoky Hill Chalk]] Member and the terrestrial fauna of the late Cretaceous [[Hell Creek Formation]]. Other important Cretaceous exposures occur in [[Europe]] (e.g., the [[Weald]]) and [[China]] (the [[Yixian Formation]]). In the area that is now India, massive [[lava bed]]s called the [[Deccan Traps]] erupted in the very late Cretaceous and early Paleocene.

==Climate==
{{further|Cool tropics paradox}}
[[Palynology|Palynological]] evidence indicates the Cretaceous climate had three broad phases: a Berriasian–Barremian warm-dry phase, an Aptian–Santonian warm-wet phase, and a Campanian–Maastrichtian cool-dry phase.<ref name="ClimatePalynology">{{cite journal |last1=Wang |first1=Jing-Yu |last2=Li |first2=Xiang-Hui |last3=Li |first3=Li-Qin |last4=Wang |first4=Yong-Dong |date=September 2022 |title=Cretaceous climate variations indicated by palynoflora in South China |url=https://www.sciencedirect.com/science/article/abs/pii/S1871174X21000895 |journal=[[Palaeoworld]] |volume=31 |issue=3 |pages=507–520 |doi=10.1016/j.palwor.2021.11.001 |s2cid=243963376 |access-date=11 December 2022}}</ref> As in the Cenozoic, the 400,000 year eccentricity cycle was the dominant orbital cycle governing carbon flux between different reservoirs and influencing global climate.<ref>{{Cite journal |last1=Giorgioni |first1=Martino |last2=Weissert |first2=Helmut |last3=Bernasconi |first3=Stefano M. |last4=Hochuli |first4=Peter A. |last5=Coccioni |first5=Rodolfo |last6=Keller |first6=Christina E. |date=21 January 2012 |title=Orbital control on carbon cycle and oceanography in the mid-Cretaceous greenhouse: LONG ECCENTRICITY CYCLES IN C-ISOTOPE |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=27 |issue=1 |pages=1–12 |doi=10.1029/2011PA002163 |s2cid=128594924 |doi-access=free }}</ref> The location of the Intertropical Convergence Zone (ITCZ) was roughly the same as in the present.<ref>{{Cite journal |last1=Hofmann |first1=P. |last2=Wagner |first2=T. |date=23 December 2011 |title=ITCZ controls on Late Cretaceous black shale sedimentation in the tropical Atlantic Ocean |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=26 |issue=4 |pages=1–11 |doi=10.1029/2011PA002154 |bibcode=2011PalOc..26.4223H |issn=0883-8305 |doi-access=free }}</ref>

The cooling trend of the last epoch of the Jurassic, the Tithonian, continued into the Berriasian, the first age of the Cretaceous.<ref name="The Berriasian Age" /> The North Atlantic seaway opened and enabled the flow of cool water from the Boreal Ocean into the Tethys.<ref>{{cite journal |last1=Abbink |first1=Oscar |last2=Targarona |first2=Jordi |last3=Brinkhuis |first3=Henk |last4=Visscher |first4=Henk |date=October 2001 |title=Late Jurassic to earliest Cretaceous palaeoclimatic evolution of the southern North Sea |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818101001011 |journal=[[Global and Planetary Change]] |volume=30 |issue=3–4 |pages=231–256 |doi=10.1016/S0921-8181(01)00101-1 |bibcode=2001GPC....30..231A |access-date=17 August 2023}}</ref> There is evidence that snowfalls were common in the higher latitudes during this age, and the tropics became wetter than during the Triassic and Jurassic. Glaciation was restricted to high-[[latitude]] mountains, though seasonal snow may have existed farther from the poles.<ref name="The Berriasian Age">{{cite web|url=http://palaeos.com/mesozoic/cretaceous/berriasian.html|title=Palaeos Mesozoic: Cretaceous: The Berriasian Age|first=M.Alan|last=Kazlev|website=Palaeos.com|access-date=18 October 2017|url-status=dead|archive-url=https://web.archive.org/web/20101220223930/http://palaeos.com/Mesozoic/Cretaceous/Berriasian.html|archive-date=20 December 2010}}</ref> After the end of the first age, however, temperatures began to increase again, with a number of thermal excursions, such as the middle [[Valanginian]] [[Weissert Event|Weissert Thermal Excursion]] (WTX),<ref name="ChristopherScotese" /> which was caused by the Paraná-Etendeka Large Igneous Province's activity.<ref>{{cite journal |last1=Martinez |first1=Mathieu |last2=Aguirre-Urreta |first2=Beatriz |last3=Dera |first3=Guillaume |last4=Lescano |first4=Marina |last5=Omarini |first5=Julieta |last6=Tunik |first6=Maisa |last7=O'Dogherty |first7=Luis |last8=Aguado |first8=Roque |last9=Company |first9=Miguel |last10=Bodin |first10=Stéphane |date=April 2023 |title=Synchrony of carbon cycle fluctuations, volcanism and orbital forcing during the Early Cretaceous |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825223000454 |journal=[[Earth-Science Reviews]] |volume=239 |doi=10.1016/j.earscirev.2023.104356 |bibcode=2023ESRv..23904356M |s2cid=256880421 |access-date=9 August 2023}}</ref> It was followed by the middle [[Hauterivian]] Faraoni Thermal Excursion (FTX) and the early [[Barremian]] Hauptblatterton Thermal Event (HTE). The HTE marked the ultimate end of the Tithonian-early Barremian Cool Interval (TEBCI).<ref name="ChristopherScotese" /> During this interval, precession was the dominant orbital driver of environmental changes in the Vocontian Basin.<ref>{{Cite journal |last1=Boulila |first1=Slah |last2=Charbonnier |first2=Guillaume |last3=Galbrun |first3=Bruno |last4=Gardin |first4=Silvia |date=1 July 2015 |title=Climatic precession is the main driver of Early Cretaceous sedimentation in the Vocontian Basin (France): Evidence from the Valanginian Orpierre succession |url=https://linkinghub.elsevier.com/retrieve/pii/S0037073815001116 |journal=[[Sedimentary Geology (journal)|Sedimentary Geology]] |language=en |volume=324 |pages=1–11 |doi=10.1016/j.sedgeo.2015.04.014 |bibcode=2015SedG..324....1B |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> For much of the TEBCI, northern Gondwana experienced a monsoonal climate.<ref>{{Cite journal |last1=Cui |first1=Xiaohui |last2=Li |first2=Xin |last3=Aitchison |first3=Jonathan C. |last4=Luo |first4=Hui |date=May 2023 |title=Early Cretaceous monsoonal upwelling along the northern margin of the Gondwana continent: Evidence from radiolarian cherts |url=https://linkinghub.elsevier.com/retrieve/pii/S0377839823000464 |journal=Marine Micropaleontology |language=en |volume=181 |pages=102247 |doi=10.1016/j.marmicro.2023.102247 |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> A shallow thermocline existed in the mid-latitude Tethys.<ref>{{Cite journal |last1=Wang |first1=Tianyang |last2=Hoffmann |first2=René |last3=He |first3=Songlin |last4=Zhang |first4=Qinghai |last5=Li |first5=Guobiao |last6=Randrianaly |first6=Hasina Nirina |last7=Xie |first7=Jing |last8=Yue |first8=Yahui |last9=Ding |first9=Lin |date=October 2023 |title=Early Cretaceous climate for the southern Tethyan Ocean: Insights from the geochemical and paleoecological analyses of extinct cephalopods |url=https://linkinghub.elsevier.com/retrieve/pii/S0921818123001935 |journal=[[Global and Planetary Change]] |language=en |volume=229 |pages=104220 |doi=10.1016/j.gloplacha.2023.104220 |bibcode=2023GPC...22904220W |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> The TEBCI was followed by the Barremian-Aptian Warm Interval (BAWI).<ref name="ChristopherScotese" /> This hot climatic interval coincides with [[Manihiki Plateau|Manihiki]] and [[Ontong Java Plateau]] volcanism and with the [[Selli Event]].<ref>{{Cite journal |last1=Larson |first1=Roger L. |last2=Erba |first2=Elisabetta |date=4 May 2010 |title=Onset of the Mid-Cretaceous greenhouse in the Barremian-Aptian: Igneous events and the biological, sedimentary, and geochemical responses |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=14 |issue=6 |pages=663–678 |doi=10.1029/1999PA900040 |doi-access=free }}</ref> Early Aptian tropical [[sea surface temperature]]s (SSTs) were 27–32&nbsp;°C, based on [[TEX86|TEX<sub>86</sub>]] measurements from the equatorial Pacific.<ref>{{cite journal |last1=Schouten |first1=Stefan |last2=Hopmans |first2=Ellen C. |last3=Forster |first3=Astrid |last4=Van Breugel |first4=Yvonne |last5=Kuypers |first5=Marcel M. M. |last6=Sinninghe Damsté |first6=Jaap S. |date=1 December 2003 |title=Extremely high sea-surface temperatures at low latitudes during the middle Cretaceous as revealed by archaeal membrane lipids |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/31/12/1069/29198/Extremely-high-sea-surface-temperatures-at-low |journal=[[Geology (journal)|Geology]] |volume=31 |issue=12 |pages=1069–1072 |doi=10.1130/G19876.1 |bibcode=2003Geo....31.1069S |hdl=21.11116/0000-0001-D1DF-8 |s2cid=129660048 |access-date=11 May 2023|hdl-access=free }}</ref> During the Aptian, Milankovitch cycles governed the occurrence of anoxic events by modulating the intensity of the hydrological cycle and terrestrial runoff.<ref>{{Cite journal |last1=Behrooz |first1=L. |last2=Naafs |first2=B. D. A. |last3=Dickson |first3=A. J. |last4=Love |first4=G. D. |last5=Batenburg |first5=S. J. |last6=Pancost |first6=R. D. |date=August 2018 |title=Astronomically Driven Variations in Depositional Environments in the South Atlantic During the Early Cretaceous |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=33 |issue=8 |pages=894–912 |doi=10.1029/2018PA003338 |bibcode=2018PaPa...33..894B |s2cid=89611847 |issn=2572-4517 |doi-access=free |hdl=1983/dd9ce325-fc6b-44a0-bab0-e0aa68943adc |hdl-access=free }}</ref> The early Aptian was also notable for its millennial scale hyperarid events in the mid-latitudes of Asia.<ref>{{Cite journal |last1=Hasegawa |first1=Hitoshi |last2=Katsuta |first2=Nagayoshi |last3=Muraki |first3=Yasushi |last4=Heimhofer |first4=Ulrich |last5=Ichinnorov |first5=Niiden |last6=Asahi |first6=Hirofumi |last7=Ando |first7=Hisao |last8=Yamamoto |first8=Koshi |last9=Murayama |first9=Masafumi |last10=Ohta |first10=Tohru |last11=Yamamoto |first11=Masanobu |last12=Ikeda |first12=Masayuki |last13=Ishikawa |first13=Kohki |last14=Kuma |first14=Ryusei |last15=Hasegawa |first15=Takashi |last16=Hasebe |first16=Noriko |last17=Nishimoto |first17=Shoji |last18=Yamaguchi |first18=Koichi |last19=Abe |first19=Fumio |last20=Tada |first20=Ryuji |last21=Nakagawa |first21=Takeshi |date=19 December 2022 |title=Decadal–centennial-scale solar-linked climate variations and millennial-scale internal oscillations during the Early Cretaceous |journal=[[Scientific Reports]] |language=en |volume=12 |issue=1 |pages=21894 |doi=10.1038/s41598-022-25815-w |pmid=36536054 |pmc=9763356 |bibcode=2022NatSR..1221894H |issn=2045-2322 }}</ref> The BAWI itself was followed by the Aptian-Albian Cold Snap (AACS) that began about 118 Ma.<ref name="ChristopherScotese" /> A short, relatively minor ice age may have occurred during this so-called "cold snap", as evidenced by glacial [[dropstone]]s in the western parts of the Tethys Ocean<ref>{{cite journal |last1=Rodríguez-López |first1=Juan Pedro |last2=Liesa |first2=Carlos L. |last3=Pardo |first3=Gonzalo |last4=Meléndez |first4=Nieves |last5=Soria |first5=Ana R. |last6=Skilling |first6=Ian |date=15 June 2016 |title=Glacial dropstones in the western Tethys during the late Aptian–early Albian cold snap: Palaeoclimate and palaeogeographic implications for the mid-Cretaceous |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821630058X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=452 |pages=11–27 |doi=10.1016/j.palaeo.2016.04.004 |bibcode=2016PPP...452...11R |access-date=19 March 2023}}</ref> and the expansion of calcareous nannofossils that dwelt in cold water into lower latitudes.<ref>{{cite journal |last1=Mutterlose |first1=Jörg |last2=Bornemann |first2=André |last3=Herrle |first3=Jens |date=May 2009 |title=The Aptian - Albian cold snap: Evidence for "mid" Cretaceous icehouse interludes |url=https://www.researchgate.net/publication/233692068 |journal=[[Neues Jahrbuch für Geologie und Paläontologie]] |volume=252 |issue=2 |pages=217–225 |doi=10.1127/0077-7749/2009/0252-0217 |bibcode=2009NJGPA.252..217M |access-date=18 June 2023}}</ref> The AACS is associated with an arid period in the [[Iberian Peninsula]].<ref>{{cite journal |last1=Diéguez |first1=Carmen |last2=Peyrot |first2=Daniel |last3=Barrón |first3=Eduardo |date=October 2010 |title=Floristic and vegetational changes in the Iberian Peninsula during Jurassic and Cretaceous |url=https://www.sciencedirect.com/science/article/abs/pii/S0034666710001223 |journal=[[Review of Palaeobotany and Palynology]] |volume=162 |issue=3 |pages=325–340 |doi=10.1016/j.revpalbo.2010.06.004 |bibcode=2010RPaPa.162..325D |access-date=18 June 2023}}</ref>

Temperatures increased drastically after the end of the AACS,<ref>{{cite journal |last1=Fletcher |first1=Tamara L. |last2=Greenwood |first2=David R. |last3=Moss |first3=Patrick T. |last4=Salisbury |first4=Steven W. |title=Paleoclimate of the Late Cretaceous (Cenomanian-Turonian) Portion of the Winton Formation, Central-Western Queensland, Australia: New Observations Based on Clamp and Bioclimatic Analysis |date=1 March 2014 |url=https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/29/3/121/146380/PALEOCLIMATE-OF-THE-LATE-CRETACEOUS-CENOMANIAN |journal=[[PALAIOS]] |volume=29 |issue=3–4 |pages=121–128 |doi=10.2110/palo.2013.080 |bibcode=2014Palai..29..121F |s2cid=128403453 |access-date=6 April 2023}}</ref> which ended around 111 Ma with the Paquier/Urbino Thermal Maximum, giving way to the Mid-Cretaceous Hothouse (MKH), which lasted from the early [[Albian]] until the early Campanian.<ref name="ChristopherScotese" /> Faster rates of seafloor spreading and entry of carbon dioxide into the atmosphere are believed to have initiated this period of extreme warmth,<ref>{{cite journal |last1=Leckie |first1=R. Mark |last2=Bralower |first2=Timothy J. |last3=Cashman |first3=Richard |date=23 August 2002 |title=Oceanic anoxic events and plankton evolution: Biotic response to tectonic forcing during the mid-Cretaceous |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001PA000623 |journal=[[Paleoceanography and Paleoclimatology]] |volume=17 |issue=3 |pages=13-1-13-29 |doi=10.1029/2001PA000623 |bibcode=2002PalOc..17.1041L |access-date=19 April 2023}}</ref> along with high flood basalt activity.<ref>{{Cite journal |last=Kerrick |first=Derrill M. |date=1 November 2001 |title=Present and past nonanthropogenic CO 2 degassing from the solid earth |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2001RG000105 |journal=[[Reviews of Geophysics]] |language=en |volume=39 |issue=4 |pages=565–585 |doi=10.1029/2001RG000105 |issn=8755-1209}}</ref> The MKH was punctuated by multiple thermal maxima of extreme warmth. The Leenhardt Thermal Event (LTE) occurred around 110 Ma, followed shortly by the l’Arboudeyesse Thermal Event (ATE) a million years later. Following these two hyperthermals was the [[Amadeus Event|Amadeus Thermal Maximum]] around 106 Ma, during the middle Albian. Then, around a million years after that, occurred the Petite Verol Thermal Event (PVTE). Afterwards, around 102.5 Ma, the Event 6 Thermal Event (EV6) took place; this event was itself followed by the Breistroffer Thermal Maximum around 101 Ma, during the latest Albian. Approximately 94 Ma, the Cenomanian-Turonian Thermal Maximum occurred,<ref name="ChristopherScotese" /> with this hyperthermal being the most extreme hothouse interval of the Cretaceous<ref>{{cite journal |last1=Vandermark |first1=Deborah |last2=Tarduno |first2=John A. |last3=Brinkman |first3=Donald B. |date=May 2007 |title=A fossil champsosaur population from the high Arctic: Implications for Late Cretaceous paleotemperatures |url=https://www.researchgate.net/publication/229407029 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=248 |issue=1–2 |pages=49–59 |doi=10.1016/j.palaeo.2006.11.008 |bibcode=2007PPP...248...49V |access-date=9 June 2023}}</ref><ref>{{cite journal |last1=Forster |first1=Astrid |last2=Schouten |first2=Stephan |last3=Moriya |first3=Kazuyoshi |last4=Wilson |first4=Paul A. |last5=Sinninghe Damsté |first5=Jaap S. |date=14 March 2007 |title=Tropical warming and intermittent cooling during the Cenomanian/Turonian oceanic anoxic event 2: Sea surface temperature records from the equatorial Atlantic |journal=[[Paleoceanography and Paleoclimatology]] |volume=22 |issue=1 |pages=1–14 |doi=10.1029/2006PA001349 |bibcode=2007PalOc..22.1219F |doi-access=free }}</ref><ref>{{cite journal |last1=O'Brien |first1=Charlotte L. |last2=Robinson |first2=Stuart A. |last3=Pancost |first3=Richard D. |last4=Sinninghe Damsté |first4=Jaap S. |last5=Schouten |first5=Stefan |last6=Lunt |first6=Daniel J. |last7=Alsenz |first7=Heiko |last8=Bornemann |first8=André |last9=Bottini |first9=Cinzia |last10=Brassell |first10=Simon C. |last11=Farnsworth |first11=Alexander |last12=Forster |first12=Astrid |last13=Huber |first13=Brian T. |last14=Inglis |first14=Gordon N. |last15=Jenkyns |first15=Hugh C. |last16=Linnert |first16=Christan |last17=Littler |first17=Kate |last18=Markwick |first18=Paul |last19=McAnena |first19=Alison |last20=Mutterlose |first20=Jörg |last21=Naafs |first21=B. David A. |last22=Püttmann |first22=Wilhelm |last23=Sluijs |first23=Appy |last24=Van Helmond |first24=Niels A.G.M. |last25=Wellekoop |first25=Johan |last26=Wagner |first26=Thomas |last27=Wrobel |first27=Neil E. |date=September 2017 |title=Cretaceous sea-surface temperature evolution: Constraints from TEX86 and planktonic foraminiferal oxygen isotopes |journal=[[Earth-Science Reviews]] |volume=172 |pages=224–247 |doi=10.1016/j.earscirev.2017.07.012 |bibcode=2017ESRv..172..224O |s2cid=55405082 |doi-access=free }}</ref> and being associated with a sea level highstand.<ref>{{Cite journal |last1=Püttmann |first1=Tobias |last2=Linnert |first2=Christian |last3=Dölling |first3=Bettina |last4=Mutterlose |first4=Jörg |date=1 July 2018 |title=Deciphering Late Cretaceous (Cenomanian to Campanian) coastline dynamics in the southwestern Münsterland (northwest Germany) by using calcareous nannofossils: Eustasy vs local tectonics |url=https://www.sciencedirect.com/science/article/pii/S0195667117301015 |journal=[[Cretaceous Research]] |series=Advances in Cretaceous palaeontology and stratigraphy – Christopher John Wood Memorial Volume |volume=87 |pages=174–184 |doi=10.1016/j.cretres.2017.07.005 |bibcode=2018CrRes..87..174P |s2cid=134356485 |issn=0195-6671 |access-date=24 November 2023}}</ref> Temperatures cooled down slightly over the next few million years, but then another thermal maximum, the Coniacian Thermal Maximum, happened, with this thermal event being dated to around 87 Ma.<ref name="ChristopherScotese" /> Atmospheric CO<sub>2</sub> levels may have varied by thousands of ppm throughout the MKH.<ref>{{cite journal |last1=Bice |first1=Karen L. |last2=Norris |first2=Richard D. |date=24 December 2002 |title=Possible atmospheric CO2 extremes of the Middle Cretaceous (late Albian–Turonian) |journal=[[Paleoceanography and Paleoclimatology]] |volume=17 |issue=4 |pages=22-1-22-17 |doi=10.1029/2002PA000778 |bibcode=2002PalOc..17.1070B |doi-access=free }}</ref> Mean annual temperatures at the poles during the MKH exceeded 14&nbsp;°C.<ref>{{cite journal |last1=Wang |first1=Yongdong |last2=Huang |first2=Chengmin |last3=Sun |first3=Bainian |last4=Quan |first4=Cheng |last5=Wu |first5=Jingyu |last6=Lin |first6=Zhicheng |date=February 2014 |title=Paleo-CO2 variation trends and the Cretaceous greenhouse climate |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825213001888 |journal=[[Earth-Science Reviews]] |volume=129 |pages=136–147 |doi=10.1016/j.earscirev.2013.11.001 |bibcode=2014ESRv..129..136W |access-date=5 April 2023}}</ref> Such hot temperatures during the MKH resulted in a very gentle [[temperature gradient]] from the [[equator]] to the poles; the latitudinal temperature gradient during the Cenomanian-Turonian Thermal Maximum was 0.54&nbsp;°C per ° latitude for the Southern Hemisphere and 0.49&nbsp;°C per ° latitude for the Northern Hemisphere, in contrast to present day values of 1.07 and 0.69&nbsp;°C per ° latitude for the Southern and Northern hemispheres, respectively.<ref>{{cite journal |last1=Laugié |first1=Marie |last2=Donnadieu |first2=Yannick |last3=Ladant |first3=Jean-Baptiste |last4=Green |first4=J. A. Mattias |last5=Bopp |first5=Laurent |last6=Raisson |first6=François |date=5 June 2020 |title=Stripping back the modern to reveal the Cenomanian–Turonian climate and temperature gradient underneath |url=https://cp.copernicus.org/articles/16/953/2020/ |journal=[[Climate of the Past]] |volume=16 |issue=3 |pages=953–971 |doi=10.5194/cp-16-953-2020 |bibcode=2020CliPa..16..953L |s2cid=219918773 |access-date=19 March 2023 |doi-access=free }}</ref> This meant weaker global winds, which drive the ocean currents, and resulted in less [[upwelling]] and more stagnant [[ocean]]s than today.<ref name="ThermalEvolutionCretaceousTethyanWaters">{{cite journal |last1=Pucéat |first1=Emmanuelle |last2=Lécuyer |first2=Christophe |last3=Sheppard |first3=Simon M. F. |last4=Dromart |first4=Gilles |last5=Reboulet |first5=Stéphane |last6=Grandjean |first6=Patricia |date=3 May 2003 |title=Thermal evolution of Cretaceous Tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels |journal=[[Paleoceanography and Paleoclimatology]] |volume=18 |issue=2 |page=1029 |doi=10.1029/2002PA000823 |bibcode=2003PalOc..18.1029P |doi-access=free }}</ref> This is evidenced by widespread black [[shale]] deposition and frequent [[anoxic event]]s.{{sfn|Stanley|1999|pp=481–482}} Tropical SSTs during the late Albian most likely averaged around 30&nbsp;°C. Despite this high SST, seawater was not hypersaline at this time, as this would have required significantly higher temperatures still.<ref>{{cite journal |last1=Norris |first1=Richard D. |last2=Wilson |first2=Paul A. |date=1 September 1998 |title=Low-latitude sea-surface temperatures for the mid-Cretaceous and the evolution of planktic foraminifera |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/26/9/823/206981/Low-latitude-sea-surface-temperatures-for-the-mid |journal=[[Geology (journal)|Geology]] |volume=26 |issue=9 |pages=823–826 |doi=10.1130/0091-7613(1998)026<0823:LLSSTF>2.3.CO;2 |bibcode=1998Geo....26..823N |access-date=5 April 2023}}</ref> On land, arid zones in the Albian regularly expanded northward in tandem with expansions of subtropical high pressure belts.<ref>{{Cite journal |last1=Hong |first1=Sung Kyung |last2=Yi |first2=Sangheon |last3=Shinn |first3=Young Jae |date=1 July 2020 |title=Middle Albian climate fluctuation recorded in the carbon isotope composition of terrestrial plant matter |url=https://www.sciencedirect.com/science/article/pii/S1367912020301449 |journal=[[Journal of Asian Earth Sciences]] |volume=196 |pages=104363 |doi=10.1016/j.jseaes.2020.104363 |bibcode=2020JAESc.19604363H |s2cid=216375103 |issn=1367-9120 |access-date=19 November 2023}}</ref> The Cedar Mountain Formation's Soap Wash flora indicates a mean annual temperature of between 19 and 26&nbsp;°C in Utah at the Albian-Cenomanian boundary.<ref>{{Cite journal |last1=Arens |first1=Nan Crystal |last2=Harris |first2=Elisha B. |date=March 2015 |title=Paleoclimatic reconstruction for the Albian–Cenomanian transition based on a dominantly angiosperm flora from the Cedar Mountain Formation, Utah, USA |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667114001943 |journal=[[Cretaceous Research]] |language=en |volume=53 |pages=140–152 |doi=10.1016/j.cretres.2014.11.004 |bibcode=2015CrRes..53..140A |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> Tropical SSTs during the Cenomanian-Turonian Thermal Maximum were at least 30&nbsp;°C,<ref>{{cite journal |last1=Wilson |first1=Paul A. |last2=Norris |first2=Richard D. |last3=Cooper |first3=Matthew J. |date=1 July 2002 |title=Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/30/7/607/191749/Testing-the-Cretaceous-greenhouse-hypothesis-using?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=30 |issue=7 |pages=607–610 |doi=10.1130/0091-7613(2002)030<0607:TTCGHU>2.0.CO;2 |bibcode=2002Geo....30..607W |access-date=5 April 2023}}</ref> though one study estimated them as high as between 33 and 42&nbsp;°C.<ref>{{cite journal |last1=Bice |first1=Karen L. |last2=Birgel |first2=Daniel |last3=Meyers |first3=Philip A. |last4=Dahl |first4=Kristina A. |last5=Hinrichs |first5=Kai-Uwe |last6=Norris |first6=Richard D. |date=8 April 2006 |title=A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005PA001203 |journal=[[Paleoceanography and Paleoclimatology]] |volume=21 |issue=2 |pages=1–17 |doi=10.1029/2005PA001203 |bibcode=2006PalOc..21.2002B |access-date=5 April 2023|hdl=2027.42/95054 |hdl-access=free }}</ref> An intermediate estimate of ~33-34&nbsp;°C has also been given.<ref>{{cite journal |last1=Norris |first1=Richard D. |last2=Bice |first2=Karen L. |last3=Magno |first3=Elizabeth A. |last4=Wilson |first4=Paul A. |date=1 April 2002 |title=Jiggling the tropical thermostat in the Cretaceous hothouse |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/30/4/299/192373/Jiggling-the-tropical-thermostat-in-the-Cretaceous |journal=[[Geology (journal)|Geology]] |volume=30 |issue=4 |pages=299–302 |doi=10.1130/0091-7613(2002)030<0299:JTTTIT>2.0.CO;2 |bibcode=2002Geo....30..299N |access-date=5 April 2023}}</ref> Meanwhile, deep ocean temperatures were as much as {{convert|15|to|20|C-change|sigfig=2}} warmer than today's<!-- Note that these are differences in temperature -->;{{sfn|Skinner| Porter|1995|p=557}}<!-- "15 higher" or "15 which is higher"? --> one study estimated that deep ocean temperatures were between 12 and 20&nbsp;°C during the MKH.<ref name="FishToothOxygen" /> The poles were so warm that [[ectothermic]] reptiles were able to inhabit them.<ref name="LateCretaceousArcticVertebrates">{{cite journal |last1=Tarduno |first1=J. A. |last2=Brinkman |first2=D. B. |last3=Renne |first3=P. R. |last4=Cottrell |first4=R. D. |last5=Scher |first5=H. |last6=Castillo |first6=P. |date=18 December 1998 |title=Evidence for Extreme Climatic Warmth from Late Cretaceous Arctic Vertebrates |url=https://www.science.org/doi/10.1126/science.282.5397.2241 |journal=[[Science (journal)|Science]] |volume=282 |issue=5397 |pages=2241–2243 |doi=10.1126/science.282.5397.2241 |pmid=9856943 |bibcode=1998Sci...282.2241T |access-date=24 July 2023}}</ref>

Beginning in the Santonian, near the end of the MKH, the global climate began to cool, with this cooling trend continuing across the Campanian.<ref>{{cite journal |last1=Petrizzo |first1=Maria Rose |last2=MacLeod |first2=Kenneth G. |last3=Watkins |first3=David K. |last4=Wolfgring |first4=Erik |last5=Huber |first5=Brian T. |date=27 December 2021 |title=Late Cretaceous Paleoceanographic Evolution and the Onset of Cooling in the Santonian at Southern High Latitudes (IODP Site U1513, SE Indian Ocean) |journal=[[Paleoceanography and Paleoclimatology]] |volume=37 |issue=1 |pages=e2021PA004353 |doi=10.1029/2021PA004353 |pmid=35910494 |pmc=9303530 }}</ref> This period of cooling, driven by falling levels of atmospheric carbon dioxide,<ref name="FishToothOxygen">{{cite journal |last1=Pucéat |first1=Emmanuelle |last2=Lécuyer |first2=Christophe |last3=Donnadieu |first3=Yannick |last4=Naveau |first4=Philippe |last5=Cappetta |first5=Henri |last6=Ramstein |first6=Gilles |last7=Huber |first7=Brian T. |last8=Kriwet |first8=Juergen |date=1 February 2007 |title=Fish tooth δ18O revising Late Cretaceous meridional upper ocean water temperature gradients |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/35/2/107/129762/Fish-tooth-18O-revising-Late-Cretaceous-meridional |journal=[[Geology (journal)|Geology]] |volume=35 |issue=2 |pages=107–110 |doi=10.1130/G23103A.1 |bibcode=2007Geo....35..107P |access-date=19 March 2023}}</ref> caused the end of the MKH and the transition into a cooler climatic interval, known formally as the Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI).<ref name="ChristopherScotese" /> Tropical SSTs declined from around 35&nbsp;°C in the early Campanian to around 28&nbsp;°C in the Maastrichtian.<ref>{{cite journal |last1=Linnert |first1=Christian |last2=Robinson |first2=Stuart A. |last3=Lees |first3=Jackie A. |last4=Bown |first4=Paul R. |last5=Pérez-Rodríguez |first5=Irene |last6=Petrizzo |first6=Maria Rose |last7=Falzoni |first7=Francesca |last8=Littler |first8=Kate |last9=Arz |first9=José Antonio |last10=Russell |first10=Ernest E. |date=17 June 2014 |title=Evidence for global cooling in the Late Cretaceous |journal=[[Nature Communications]] |volume=5 |page=4194 |doi=10.1038/ncomms5194 |pmid=24937202 |pmc=4082635 |bibcode=2014NatCo...5.4194L }}</ref> Deep ocean temperatures declined to 9 to 12&nbsp;°C,<ref name="FishToothOxygen" /> though the shallow temperature gradient between tropical and polar seas remained.<ref>{{cite journal |last1=O'Connor |first1=Lauren K. |last2=Robinson |first2=Stuart A. |last3=Naafs |first3=B. David A. |last4=Jenkyns |first4=Hugh C. |last5=Henson |first5=Sam |last6=Clarke |first6=Madeleine |last7=Pancost |first7=Richard D. |date=27 February 2019 |title=Late Cretaceous Temperature Evolution of the Southern High Latitudes: A TEX86 Perspective |journal=[[Paleoceanography and Paleoclimatology]] |volume=34 |issue=4 |pages=436–454 |doi=10.1029/2018PA003546 |bibcode=2019PaPa...34..436O |s2cid=134095694 |doi-access=free |hdl=1983/9c306756-d31c-4cda-b68e-4ba6f0bf9d44 |hdl-access=free }}</ref> Regional conditions in the [[Western Interior Seaway]] changed little between the MKH and the LKEPCI.<ref>{{cite journal |last1=Wang |first1=Chengshan |last2=Scott |first2=Robert W. |last3=Wan |first3=Xiaoqiao |last4=Graham |first4=Stephan A. |last5=Huang |first5=Yongjian |last6=Wang |first6=Pujun |last7=Wu |first7=Huaichun |last8=Dean |first8=Walter E. |last9=Zhang |first9=Laiming |date=November 2013 |title=Late Cretaceous climate changes recorded in Eastern Asian lacustrine deposits and North American Epieric sea strata |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825213001499 |journal=[[Earth-Science Reviews]] |volume=126 |pages=275–299 |doi=10.1016/j.earscirev.2013.08.016 |bibcode=2013ESRv..126..275W |access-date=19 March 2023}}</ref> During this period of relatively cool temperatures, the ITCZ became narrower,<ref>{{Cite journal |last1=Ma |first1=Mingming |last2=He |first2=Mei |last3=Zhao |first3=Mengting |last4=Peng |first4=Chao |last5=Liu |first5=Xiuming |date=1 April 2021 |title=Evolution of atmospheric circulation across the Cretaceous–Paleogene (K–Pg) boundary interval in low-latitude East Asia |url=https://www.sciencedirect.com/science/article/pii/S0921818121000205 |journal=[[Global and Planetary Change]] |volume=199 |pages=103435 |doi=10.1016/j.gloplacha.2021.103435 |bibcode=2021GPC...19903435M |s2cid=233573257 |issn=0921-8181 |access-date=18 November 2023}}</ref> while the strength of both summer and winter monsoons in East Asia was directly correlated to atmospheric [[Carbon dioxide|CO<sub>2</sub>]] concentrations.<ref>{{Cite journal |last1=Chen |first1=Junming |last2=Zhao |first2=Ping |last3=Wang |first3=Chengshan |last4=Huang |first4=Yongjian |last5=Cao |first5=Ke |date=1 September 2013 |title=Modeling East Asian climate and impacts of atmospheric CO2 concentration during the Late Cretaceous (66Ma) |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |series=Environmental/Climate Change in the Cretaceous Greenhouse World: records from terrestrial scientific drilling of Songliao Basin and adjacent area of China |volume=385 |pages=190–201 |doi=10.1016/j.palaeo.2012.07.017 |bibcode=2013PPP...385..190C |issn=0031-0182 |doi-access=free }}</ref> Laramidia likewise had a seasonal, monsoonal climate.<ref>{{Cite journal |last1=Fricke |first1=Henry C. |last2=Foreman |first2=Brady Z. |last3=Sewall |first3=Jacob O. |date=15 January 2010 |title=Integrated climate model-oxygen isotope evidence for a North American monsoon during the Late Cretaceous |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X09006177 |journal=[[Earth and Planetary Science Letters]] |language=en |volume=289 |issue=1–2 |pages=11–21 |doi=10.1016/j.epsl.2009.10.018 |bibcode=2010E&PSL.289...11F |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> The Maastrichtian was a time of chaotic, highly variable climate.<ref>{{Cite journal |last=Barrera |first=Enriqueta |date=1 October 1994 |title=Global environmental changes preceding the Cretaceous-Tertiary boundary: Early-late Maastrichtian transition |url=https://pubs.geoscienceworld.org/geology/article/22/10/877-880/188033 |journal=[[Geology (journal)|Geology]] |language=en |volume=22 |issue=10 |pages=877–880 |doi=10.1130/0091-7613(1994)022<0877:GECPTC>2.3.CO;2 |bibcode=1994Geo....22..877B |issn=0091-7613 |access-date=19 November 2023}}</ref> Two upticks in global temperatures are known to have occurred during the Maastrichtian, bucking the trend of overall cooler temperatures during the LKEPCI. Between 70 and 69 Ma and 66–65 Ma, isotopic ratios indicate elevated atmospheric CO<sub>2</sub> pressures with levels of 1000–1400 ppmV and mean annual temperatures in [[west Texas]] between {{convert|21|and|23|C|F}}. Atmospheric CO<sub>2</sub> and temperature relations indicate a doubling of pCO<sub>2</sub> was accompanied by a ~0.6&nbsp;°C increase in temperature.<ref>{{cite magazine |last1=Nordt |first1=Lee |first2=Stacy |last2=Atchley |first3=Steve |last3=Dworkin |title=Terrestrial Evidence for Two Greenhouse Events in the Latest Cretaceous |magazine=[[GSA Today]] |volume=13 |issue=12 |date= December 2003 |page=4 |doi=10.1130/1052-5173(2003)013<4:TEFTGE>2.0.CO;2}}</ref> The latter warming interval, occurring at the very end of the Cretaceous, was triggered by the activity of the Deccan Traps.<ref>{{cite journal |last1=Gao |first1=Yuan |last2=Ibarra |first2=Daniel E. |last3=Caves Rubenstein |first3=Jeremy K. |last4=Chen |first4=Jiuquan |last5=Kukla |first5=Tyler |last6=Methner |first6=Katharina |last7=Gao |first7=Youfeng |last8=Huang |first8=He |last9=Lin |first9=Zhipeng |last10=Zhang |first10=Laiming |last11=Xi |first11=Dangpeng |last12=Wu |first12=Huaichun |last13=Carroll |first13=Alan R. |last14=Graham |first14=Stephan A. |last15=Chamberlain |first15=C. Page |last16=Wang |first16=Changshan |date=May 2021 |title=Terrestrial climate in mid-latitude East Asia from the latest Cretaceous to the earliest Paleogene: A multiproxy record from the Songliao Basin in northeastern China |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825221000714 |journal=[[Earth-Science Reviews]] |volume=216 |pages=1–29 |doi=10.1016/j.earscirev.2021.103572 |bibcode=2021ESRv..21603572G |s2cid=233918778 |access-date=21 July 2023}}</ref> The LKEPCI lasted into the [[Late Paleocene|Late Palaeocene]], when it gave way to another supergreenhouse interval.<ref name="ChristopherScotese">{{Cite journal |last1=Scotese |first1=Christopher R. |last2=Song |first2=Haijun |last3=Mills |first3=Benjamin J. W. |last4=van der Meer |first4=Douwe G. |date=April 2021 |title=Phanerozoic paleotemperatures: The earth's changing climate during the last 540 million years |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825221000027 |journal=[[Earth-Science Reviews]] |volume=215 |pages=103503 |bibcode=2021ESRv..21503503S |doi=10.1016/j.earscirev.2021.103503 |issn=0012-8252 |archive-url=https://web.archive.org/web/20210108000000/http://dx.doi.org/10.1016/j.earscirev.2021.103503 |archive-date=8 January 2021 |s2cid=233579194 |access-date=18 March 2023}}</ref>

[[File:Cretacico-isotermas-y-mapamundi.svg|thumb|left|A computer-simulated model of surface conditions in Middle Cretaceous, 100 mya, displaying the approximate shoreline and calculated [[Isotherm (contour line)|isotherm]]s]]
The production of large quantities of magma, variously attributed to [[mantle plume]]s or to [[extensional tectonics]],<ref name=Foulger>{{cite book |title=Plates vs. Plumes: A Geological Controversy |author=Foulger, G.R. |url=http://www.wiley.com/WileyCDA/WileyTitle/productCd-1405161485.html |year=2010 |isbn=978-1-4051-6148-0 |publisher=Wiley-Blackwell}}</ref> further pushed sea levels up, so that large areas of the continental crust were covered with shallow seas. The [[Tethys Sea]] connecting the tropical oceans east to west also helped to warm the global climate. Warm-adapted [[plant fossil]]s are known from localities as far north as [[Alaska]] and [[Greenland]], while [[dinosaur]] fossils have been found within 15 degrees of the Cretaceous [[south pole]].{{sfn|Stanley|1999|p=480–482}} It was suggested that there was [[Antarctica|Antarctic]] marine glaciation in the [[Turonian]] Age, based on isotopic evidence.<ref>{{cite journal |last1=Bornemann |first1=Norris R. D. |last2=Friedrich |first2=O. |last3=Beckmann |first3=B. |last4=Schouten |first4=Stefan |last5=Sinnighe Damsté |first5=Jaap S. |last6=Vogel |first6=J. |last7=Hofmann |first7=P. |last8=Wagner |first8=T. |s2cid=206509273 |date=January 2008 |title=Isotopic evidence for glaciation during the Cretaceous supergreenhouse |url=https://www.researchgate.net/publication/5662444 |journal=[[Science (journal)|Science]] |volume=319 |issue=5860 |pages=189–192 |doi=10.1126/science.1148777 |pmid=18187651 |bibcode=2008Sci...319..189B |access-date=18 March 2023}}</ref> However, this has subsequently been suggested to be the result of inconsistent isotopic proxies,<ref>{{Cite journal |last1=Huber |first1=Brian T. |last2=MacLeod |first2=Kenneth G. |last3=Watkins |first3=David K. |last4=Coffin |first4=Millard F. |date=2018-08-01 |title=The rise and fall of the Cretaceous Hot Greenhouse climate |url=http://www.sciencedirect.com/science/article/pii/S0921818117306483 |journal=[[Global and Planetary Change]] |language=en |volume=167 |pages=1–23 |doi=10.1016/j.gloplacha.2018.04.004 |bibcode=2018GPC...167....1H |issn=0921-8181 |hdl=1912/10514 |s2cid=135295956 |hdl-access=free |access-date=18 March 2023}}</ref> with evidence of polar rainforests during this time interval at 82° S.<ref>{{Cite journal|last1=the Science Team of Expedition PS104 |last2=Klages |first2=Johann P. |last3=Salzmann |first3=Ulrich |last4=Bickert |first4=Torsten |last5=Hillenbrand |first5=Claus-Dieter |last6=Gohl |first6=Karsten |last7=Kuhn |first7=Gerhard |last8=Bohaty |first8=Steven M. |last9=Titschack |first9=Jürgen |last10=Müller |first10=Juliane |last11=Frederichs |first11=Thomas |date=April 2020 |title=Temperate rainforests near the South Pole during peak Cretaceous warmth |url=http://www.nature.com/articles/s41586-020-2148-5 |journal=[[Nature (journal)|Nature]] |language=en |volume=580 |issue=7801 |pages=81–86 |doi=10.1038/s41586-020-2148-5 |pmid=32238944 |bibcode=2020Natur.580...81K |s2cid=214736648 |issn=0028-0836 |access-date=18 March 2023}}</ref> Rafting by ice of stones into marine environments occurred during much of the Cretaceous, but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the [[Eromanga Basin]] in southern [[Australia]].<ref>{{Cite journal | last1 = Alley | first1 = N. F. | last2 = Frakes | first2 = L. A. | doi = 10.1046/j.1440-0952.2003.00984.x | title = First known Cretaceous glaciation: Livingston Tillite Member of the Cadna-owie Formation, South Australia | journal = [[Australian Journal of Earth Sciences]] | volume = 50 | issue = 2 | pages = 139–144 | year = 2003 |bibcode = 2003AuJES..50..139A | s2cid = 128739024 }}</ref><ref>{{Cite journal | last1 = Frakes | first1 = L. A. | last2 = Francis | first2 = J. E. | doi = 10.1038/333547a0 | title = A guide to Phanerozoic cold polar climates from high-latitude ice-rafting in the Cretaceous | journal = [[Nature (journal)|Nature]] | volume = 333 | issue = 6173 | pages = 547–549 | year = 1988 |bibcode = 1988Natur.333..547F | s2cid = 4344903 }}</ref>

== Flora ==
[[File:Archaefructus_liaoningensis.jpg|thumb|Facsimile of a fossil of ''Archaefructus'' from the Yixian Formation, China]]
[[File:Jaguariba wiersemana, Brazil - Museum fur Naturkunde, Berlin - MB. Pb. 1999-614.jpg|thumb|right|Fossil ''[[Jaguariba wiersemana]]'' specimen in the collection of the [[Natural History Museum, Berlin]], Germany]]
{{main|Cretaceous Terrestrial Revolution}}
[[Flowering plant]]s (angiosperms) make up around 90% of living plant species today. Prior to the rise of angiosperms, during the Jurassic and the Early Cretaceous, the higher flora was dominated by [[gymnosperm]] groups, including [[cycad]]s, [[Pinophyta|conifers]], [[ginkgophyte]]s, [[Gnetophyta|gnetophytes]] and close relatives, as well as the extinct [[Bennettitales]]. Other groups of plants included [[Pteridospermatophyta|pteridosperms]] or "seed ferns", a collective term that refers to disparate groups of extinct seed plants with fern-like foliage, including groups such as [[Corystospermaceae]] and [[Caytoniales]]. The exact origins of angiosperms are uncertain, although molecular evidence suggests that they are not closely related to any living group of gymnosperms.<ref name="Coiro-2019" />

The earliest widely accepted evidence of flowering plants are monosulcate (single-grooved) [[pollen]] grains from the late [[Valanginian]] (~ 134 million years ago) found in Israel<ref>{{cite book |last1=Brenner |first1=G.J. |title=Flowering Plant Origin, Evolution & Phylogeny |chapter=Evidence for the Earliest Stage of Angiosperm Pollen Evolution: A Paleoequatorial Section from Israel |editor1-last=Taylor |editor1-first=D.W. |editor2-last=Hickey |editor2-first=L.J. |date=1996 |isbn=978-0-585-23095-5 |pages=91–115 |location=New York |publisher=Chapman & Hall |doi=10.1007/978-0-585-23095-5_5}}</ref> and Italy,<ref>Trevisan L. 1988. Angiospermous pollen (monosulcate–trichotomosulcate phase) from the very early Lower Cretaceous of southern Tuscany (Italy): some aspects. 7th International Palynological Congress Abstracts Volume. Brisbane, Australia: University of Queensland, 165.</ref> initially at low abundance. [[Molecular clock]] estimates conflict with fossil estimates, suggesting the diversification of [[Crown group|crown-group]] angiosperms during the Late Triassic or the Jurassic, but such estimates are difficult to reconcile with the heavily sampled pollen record and the distinctive tricolpate to tricolporoidate (triple grooved) pollen of [[Eudicots|eudicot]] angiosperms.<ref name="Coiro-2019">{{Cite journal|last1=Coiro|first1=Mario|last2=Doyle|first2=James A.|last3=Hilton|first3=Jason|date=July 2019|title=How deep is the conflict between molecular and fossil evidence on the age of angiosperms?|journal=New Phytologist|language=en|volume=223|issue=1|pages=83–99|doi=10.1111/nph.15708|pmid=30681148|issn=0028-646X|doi-access=free|bibcode=2019NewPh.223...83C }}</ref> Among the oldest records of Angiosperm [[macrofossil]]s are ''[[Montsechia]]'' from the [[Barremian]] aged [[La Huérguina Formation|Las Hoyas]] beds of Spain and ''[[Archaefructus]]'' from the Barremian-Aptian boundary [[Yixian Formation]] in China. Tricolpate pollen distinctive of eudicots first appears in the Late Barremian, while the earliest remains of [[monocots]] are known from the [[Aptian]].<ref name="Coiro-2019" /> Flowering plants underwent a rapid radiation beginning during the middle Cretaceous, becoming the dominant group of land plants by the end of the period, coincident with the decline of previously dominant groups such as conifers.<ref>{{Cite journal|last1=Condamine|first1=Fabien L.|last2=Silvestro|first2=Daniele|last3=Koppelhus|first3=Eva B.|last4=Antonelli|first4=Alexandre|date=2020-11-17|title=The rise of angiosperms pushed conifers to decline during global cooling|journal=[[Proceedings of the National Academy of Sciences of the United States of America]]|language=en|volume=117|issue=46|pages=28867–28875|doi=10.1073/pnas.2005571117|issn=0027-8424|pmc=7682372|pmid=33139543|bibcode=2020PNAS..11728867C |doi-access=free }}</ref> The oldest known fossils of [[Poaceae|grasses]] are from the [[Albian]],<ref>{{Cite journal|last1=Wu|first1=Yan|last2=You|first2=Hai-Lu|last3=Li|first3=Xiao-Qiang|date=2018-09-01|title=Dinosaur-associated Poaceae epidermis and phytoliths from the Early Cretaceous of China|url=https://academic.oup.com/nsr/article/5/5/721/4769666|journal=National Science Review|language=en|volume=5|issue=5|pages=721–727|doi=10.1093/nsr/nwx145|issn=2095-5138|doi-access=free}}</ref> with the family having diversified into modern groups by the end of the Cretaceous.<ref>{{Cite journal|last1=Prasad|first1=V.|last2=Strömberg|first2=C. a. E.|last3=Leaché|first3=A. D.|last4=Samant|first4=B.|last5=Patnaik|first5=R.|last6=Tang|first6=L.|last7=Mohabey|first7=D. M.|last8=Ge|first8=S.|last9=Sahni|first9=A.|date=2011-09-20|title=Late Cretaceous origin of the rice tribe provides evidence for early diversification in Poaceae|journal=[[Nature Communications]]|language=en|volume=2|issue=1|pages=480|doi=10.1038/ncomms1482|pmid=21934664|bibcode=2011NatCo...2..480P|issn=2041-1723|doi-access=free}}</ref> The oldest large angiosperm trees are known from the [[Turonian]] (c. 90 Mya) of New Jersey, with the trunk having a preserved diameter of {{convert|1.8|m|ft}} and an estimated height of {{convert|50|m|ft}}.<ref>{{Cite journal|last1=Jud|first1=Nathan A.|last2=D’Emic|first2=Michael D.|last3=Williams|first3=Scott A.|last4=Mathews|first4=Josh C.|last5=Tremaine|first5=Katie M.|last6=Bhattacharya|first6=Janok|date=September 2018|title=A new fossil assemblage shows that large angiosperm trees grew in North America by the Turonian (Late Cretaceous)|url= |journal=[[Science Advances]]|language=en|volume=4|issue=9|pages=eaar8568|doi=10.1126/sciadv.aar8568|issn=2375-2548|pmc=6157959|pmid=30263954|bibcode=2018SciA....4.8568J}}</ref>

During the Cretaceous, [[fern]]s in the order [[Polypodiales]], which make up 80% of living fern species, would also begin to diversify.<ref>{{Cite journal|last1=Regalado|first1=Ledis|last2=Schmidt|first2=Alexander R.|last3=Müller|first3=Patrick|last4=Niedermeier|first4=Lisa|last5=Krings|first5=Michael|last6=Schneider|first6=Harald|date=July 2019|title=Heinrichsia cheilanthoides gen. et sp. nov., a fossil fern in the family Pteridaceae (Polypodiales) from the Cretaceous amber forests of Myanmar|journal=[[Journal of Systematics and Evolution]]|language=en|volume=57|issue=4|pages=329–338|doi=10.1111/jse.12514|issn=1674-4918|doi-access=free|bibcode=2019JSyEv..57..329R }}</ref>

==Terrestrial fauna==
On land, [[mammal]]s were generally small sized, but a very relevant component of the [[Fauna (animals)|fauna]], with [[cimolodont]] [[multituberculates]] outnumbering dinosaurs in some sites.<ref>{{cite book |last1=Kielan-Jaworowska |first1=Zofia |first2=Richard L. |last2=Cifelli |first3=Zhe-Xi |last3=Luo|year=2005 |title=Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure |url=https://archive.org/details/mammalsfromagedi00kiel_769 |url-access=limited |page=[https://archive.org/details/mammalsfromagedi00kiel_769/page/n317 299] |publisher=Columbia University Press |isbn=9780231119184}}</ref> Neither true [[marsupial]]s nor [[placental]]s existed until the very end,<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]] |volume=283 |issue=1833 |pages=20153026 |doi=10.1098/rspb.2015.3026 |pmc=4936024 |pmid=27358361 }}</ref> but a variety of non-marsupial [[metatheria]]ns and non-placental [[eutherian]]s had already begun to diversify greatly, ranging as carnivores ([[Deltatheroida]]), aquatic foragers ([[Stagodontidae]]) and herbivores (''[[Schowalteria]]'', [[Zhelestidae]]). Various "archaic" groups like [[eutriconodont]]s were common in the Early Cretaceous, but by the Late Cretaceous northern mammalian faunas were dominated by multituberculates and [[theria]]ns, with [[dryolestoid]]s dominating [[South America]].

The [[apex predator]]s were [[archosaur]]ian [[reptile]]s, especially [[dinosaur]]s, which were at their most diverse stage. Avians such as the ancestors of modern-day [[birds]] also diversified. They inhabited every continent, and were even found in cold polar latitudes. [[Pterosaur]]s were common in the early and middle Cretaceous, but as the Cretaceous proceeded they declined for poorly understood reasons (once thought to be due to competition with early [[bird]]s, but now it is understood avian [[adaptive radiation]] is not consistent with pterosaur decline<ref>{{Cite book| title = Pterosaurs: Natural History, Evolution, Anatomy|author=Wilton, Mark P. |isbn=978-0691150611|year=2013|publisher=Princeton University Press }}</ref>). By the end of the period only three highly specialized [[Family (biology)|families]] remained; [[Pteranodontidae]], [[Nyctosauridae]], and [[Azhdarchidae]].<ref>{{Cite journal|last1=Longrich|first1=Nicholas R.|last2=Martill|first2=David M.|last3=Andres|first3=Brian|date=2018-03-13|title=Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary|journal=PLOS Biology|language=en|volume=16|issue=3|pages=e2001663|doi=10.1371/journal.pbio.2001663|issn=1545-7885|pmc=5849296|pmid=29534059 |doi-access=free }}</ref>

The [[Liaoning]] [[lagerstätte]] ([[Yixian Formation]]) in China is an important site, full of preserved remains of numerous types of small dinosaurs, birds and mammals, that provides a glimpse of life in the Early Cretaceous. The [[coelurosaur]] dinosaurs found there represent types of the group [[Maniraptora]], which includes modern birds and their closest non-avian relatives, such as [[dromaeosaurs]], [[oviraptorosaurs]], [[therizinosaurs]], [[troodontids]] along with other [[avialans]]. Fossils of these dinosaurs from the [[Liaoning]] [[lagerstätte]] are notable for the presence of hair-like [[feather]]s.

[[Insect]]s diversified during the Cretaceous, and the oldest known [[ant]]s, [[termite]]s and some [[lepidoptera]]ns, akin to [[Butterfly|butterflies]] and [[moth]]s, appeared. [[Aphid]]s, [[grasshopper]]s and [[gall wasp]]s appeared.<ref name="UCMP" />
<gallery class="center">
File:Tyrannosaurus-rex-Profile-steveoc86.png|''[[Tyrannosaurus|Tyrannosaurus rex]]'', one of the largest land predators of all time, lived during the Late Cretaceous
File: Velociraptor Restoration.png|Up to 2 m long and 0.5 m high at the hip, ''[[Velociraptor]]'' was feathered and roamed the Late Cretaceous
File: Triceratops by Tom Patker.png|''[[Triceratops]]'', one of the most recognizable genera of the Cretaceous
File:Quetzalcoatlus07.jpg|The [[azhdarchid]] ''[[Quetzalcoatlus]]'', one of the largest animals to ever fly, lived during the Late Cretaceous
File:Confuciusornis sanctus mmartyniuk.png|''[[Confuciusornis]]'', a genus of crow-sized birds from the Early Cretaceous
File:Ichthyornis restoration.jpeg|''[[Ichthyornis]]'' was a toothed, [[seabird]]-like [[ornithuran]] from the Late Cretaceous
</gallery>

=== Rhynchocephalians ===
[[File:Priosphenodon_skeleton.png|thumb|Skeleton of ''[[Priosphenodon|Priosphenodon avelasi]]'' a large herbivorous rhynchocephalian known from the mid-Cretaceous of South America]][[Rhynchocephalia]]ns (which today only includes the [[tuatara]]) disappeared from North America and Europe after the [[Early Cretaceous]],<ref name="Cleary-2018">{{cite journal|vauthors=Cleary TJ, Benson RB, Evans SE, Barrett PM|date=March 2018|title=Lepidosaurian diversity in the Mesozoic-Palaeogene: the potential roles of sampling biases and environmental drivers|journal=Royal Society Open Science|volume=5|issue=3|pages=171830|bibcode=2018RSOS....571830C|doi=10.1098/rsos.171830|pmc=5882712|pmid=29657788}}</ref> and were absent from North Africa<ref name="Apesteguía-2016">{{cite journal|vauthors=Apesteguía S, Daza JD, Simões TR, Rage JC|date=September 2016|title=The first iguanian lizard from the Mesozoic of Africa|journal=Royal Society Open Science|volume=3|issue=9|pages=160462|bibcode=2016RSOS....360462A|doi=10.1098/rsos.160462|pmc=5043327|pmid=27703708}}</ref> and northern South America<ref>{{cite journal|vauthors=Simões TR, Wilner E, Caldwell MW, Weinschütz LC, Kellner AW|date=August 2015|title=A stem acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana|journal=[[Nature Communications]]|volume=6|issue=1|pages=8149|bibcode=2015NatCo...6.8149S|doi=10.1038/ncomms9149|pmc=4560825|pmid=26306778}}</ref> by the early [[Late Cretaceous]]. The cause of the decline of Rhynchocephalia remains unclear, but has often been suggested to be due to competition with advanced lizards and mammals.<ref name="Jones-2009">{{cite journal|vauthors=Jones ME, Tennyson AJ, Worthy JP, Evans SE, Worthy TH|date=April 2009|title=A sphenodontine (Rhynchocephalia) from the Miocene of New Zealand and palaeobiogeography of the tuatara (Sphenodon)|journal=Proceedings. Biological Sciences|volume=276|issue=1660|pages=1385–90|doi=10.1098/rspb.2008.1785|pmc=2660973|pmid=19203920}}</ref> They appear to have remained diverse in high-latitude southern South America during the Late Cretaceous, where lizards remained rare, with their remains outnumbering terrestrial lizards 200:1.<ref name="Apesteguía-2016" />

=== Choristodera ===
[[File:Philydrosaurus proseilus NMNS.jpg|thumb|''[[Philydrosaurus]]'', a choristodere from the Early Cretaceous of China]]
[[Choristodera|Choristoderes]], a group of freshwater aquatic reptiles that first appeared during the preceding Jurassic, underwent a major [[evolutionary radiation]] in Asia during the Early Cretaceous, which represents the high point of choristoderan diversity, including long necked forms such as ''[[Hyphalosaurus]]'' and the first records of the gharial-like [[Neochoristodera]], which appear to have evolved in the regional absence of aquatic [[neosuchia]]n crocodyliformes. During the Late Cretaceous the neochoristodere ''[[Champsosaurus]]'' was widely distributed across western North America.<ref name="Matsumoto-2010">{{cite journal|vauthors=Matsumoto R, Evans SE|year=2010|title=Choristoderes and the freshwater assemblages of Laurasia|journal=[[Journal of Iberian Geology]]|volume=36|issue=2|pages=253–274|doi=10.5209/rev_jige.2010.v36.n2.11|bibcode=2010JIbG...36..253M |doi-access=free}}</ref> Due to the extreme climatic warmth in the Arctic, choristoderans were able to colonise it too during the Late Cretaceous.<ref name="LateCretaceousArcticVertebrates" />

==Marine fauna==
In the seas, [[batoidea|rays]], modern [[shark]]s and [[teleost]]s became common.<ref>{{cite web|url=http://www.talkorigins.org/origins/geo_timeline.html|title=EVOLUTIONARY/GEOLOGICAL TIMELINE v1.0|website=www.TalkOrigins.org|access-date=18 October 2017}}</ref> Marine reptiles included [[ichthyosaur]]s in the early and mid-Cretaceous (becoming extinct during the late Cretaceous [[Cenomanian-Turonian anoxic event]]), [[plesiosaur]]s throughout the entire period, and [[mosasaur]]s appearing in the Late Cretaceous. Sea turtles in the form of [[Cheloniidae]] and [[Panchelonioidea]] lived during the period and survived the extinction event. Panchelonioidea is today represented by a single species; the [[leatherback sea turtle]]. The [[Hesperornithiformes]] were flightless, marine diving birds that swam like [[grebe]]s.

''[[Baculites]]'', an [[ammonite]] genus with a straight shell, flourished in the seas along with reef-building [[rudist]] clams. [[Inoceramidae|Inoceramids]] were also particularly notable among Cretaceous bivalves,<ref>{{Cite journal |last1=Walaszczyk |first1=I. |last2=Szasz |first2=L. |date=1 December 1997 |title=Inoceramid bivalves from the Turonian/Coniacian (Cretaceous) boundary in Romania: revisions of Simonescu's (1899) material from Ürmös (Ormenis), Transylvania |url=https://www.sciencedirect.com/science/article/pii/S0195667197900860 |journal=[[Cretaceous Research]] |volume=18 |issue=6 |pages=767–787 |doi=10.1006/cres.1997.0086 |bibcode=1997CrRes..18..767W |issn=0195-6671 |access-date=24 November 2023}}</ref> and they have been used to identify major biotic turnovers such as at the Turonian-Coniacian boundary.<ref>{{Cite journal |last1=Wood |first1=Christopher J. |last2=Ernst |first2=Gundolf |last3=Rasemann |first3=Gabriele |date=11 September 1984 |title=The Turonian-Coniacian stage boundary in Lower Saxony (Germany) and adjacent areas: the Salzgitter-Salder Quarry as a proposed international standard section |url=https://2dgf.dk/xpdf/bull33-01-02-225-238.pdf |journal=Bulletin of the Geological Society of Denmark |language=en |volume=33 |pages=225–238 |doi=10.37570/bgsd-1984-33-21 |bibcode=1984BuGSD..33..225W |issn=2245-7070}}</ref><ref>{{cite journal |last1=Walaszczyk |first1=Ireneusz Piotr |last2=Cobban |first2=W. A. |date=January 1998 |title=The Turonian - Coniacian boundary in the United States Western interior |url=https://www.researchgate.net/publication/287488582 |journal=[[Acta Geologica Polonica]] |volume=48 |issue=4 |pages=495–507 |access-date=24 November 2023}}</ref> Predatory gastropods with drilling habits were widespread.<ref>{{Cite journal |last=Kosnik |first=Matthew A. |date=1 September 2005 |title=Changes in Late Cretaceous–early Tertiary benthic marine assemblages: analyses from the North American coastal plain shallow shelf |url=https://bioone.org/journals/paleobiology/volume-31/issue-3/0094-8373_2005_031_0459_CILCTB_2.0.CO_2/Changes-in-Late-Cretaceousearly-Tertiary-benthic-marine-assemblages--analyses/10.1666/0094-8373(2005)031[0459:CILCTB]2.0.CO;2.short |journal=[[Paleobiology (journal)|Paleobiology]] |language=en |volume=31 |issue=3 |pages=459–479 |doi=10.1666/0094-8373(2005)031[0459:CILCTB]2.0.CO;2 |s2cid=130932162 |issn=0094-8373 |access-date=22 September 2023}}</ref> Globotruncanid [[foraminifera]] and [[echinoderms]] such as sea urchins and [[Asteroidea|starfish (sea stars)]] thrived. [[Ostracods]] were abundant in Cretaceous marine settings; ostracod species characterised by high male sexual investment had the highest rates of extinction and turnover.<ref>{{cite journal |last1=Fernandes Martins |first1=Maria João |last2=Puckett |first2=Mark |last3=Lockwood |first3=Rowan |last4=Swaddle |first4=John P. |last5=Hunt |first5=Gene |date=11 April 2018 |title=High male sexual investment as a driver of extinction in fossil ostracods |url=https://www.researchgate.net/publication/324504488 |journal=[[Nature (journal)|Nature]] |volume=556 |issue=7701 |pages=366–369 |doi=10.1038/s41586-018-0020-7 |pmid=29643505 |bibcode=2018Natur.556..366M |s2cid=256767945 |access-date=31 March 2023}}</ref> [[Thylacocephala]], a class of crustaceans, went extinct in the Late Cretaceous. The first radiation of the [[diatom]]s (generally [[silicon dioxide|siliceous]] shelled, rather than [[calcareous]]) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the [[Miocene]].<ref name="UCMP">{{cite web|url=http://www.ucmp.berkeley.edu/mesozoic/cretaceous/cretlife.html|title=Life of the Cretaceous|website=www.ucmp.Berkeley.edu|access-date=18 October 2017}}</ref> Calcareous nannoplankton were important components of the marine microbiota and important as biostratigraphic markers and recorders of environmental change.<ref>{{Cite journal |last=Lees |first=Jackie A. |date=February 2008 |title=The calcareous nannofossil record across the Late Cretaceous Turonian/Coniacian boundary, including new data from Germany, Poland, the Czech Republic and England |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667107000961 |journal=[[Cretaceous Research]] |language=en |volume=29 |issue=1 |pages=40–64 |doi=10.1016/j.cretres.2007.08.002 |bibcode=2008CrRes..29...40L |access-date=24 November 2023}}</ref>

The Cretaceous was also an important interval in the evolution of [[bioerosion]], the production of borings and scrapings in rocks, [[hardgrounds]] and shells.
<gallery class="center">
File:Kronosaurus hunt1DB.jpg|A scene from the early Cretaceous: a ''[[Woolungasaurus]]'' is attacked by a ''[[Kronosaurus]]''.
File:Tylosaurus pembinensis 1DB.jpg|''[[Tylosaurus]]'' was a large [[mosasaur]], carnivorous marine reptiles that emerged in the late Cretaceous.
File:Hesperornis BW (white background).jpg|Strong-swimming and toothed predatory waterbird ''[[Hesperornis]]'' roamed late Cretacean oceans.
File:DiscoscaphitesirisCretaceous.jpg|The [[ammonite]] ''[[Discoscaphites]] iris'', Owl Creek Formation (Upper Cretaceous), Ripley, Mississippi
File:The fossils from Cretaceous age found in Lebanon.jpg|A plate with ''[[Nematonotus]] sp.'', ''Pseudostacus sp.'' and a partial ''Dercetis triqueter'', found in [[Hakel]], Lebanon
File:Cretoxyrhina attacking Pteranodon.png|''[[Cretoxyrhina]]'', one of the largest Cretaceous [[shark]]s, attacking a ''[[Pteranodon]]'' in the [[Western Interior Seaway]]
</gallery>

==See also==
{{Portal|Paleontology}}
* [[Cretaceous–Paleogene extinction event|Cretaceous-Paleogene extinction]]
* [[Cretaceous Thermal Maximum]]
* [[List of fossil sites]] (with link directory)
* [[South Polar region of the Cretaceous]]

{{clear}}

==References==
===Citations===
{{reflist|30em}}

===Bibliography===
* {{Cite journal |author1 = Yuichiro Kashiyama |author2 = Nanako O. Ogawa |author3= Junichiro Kuroda | author4 = Motoo Shiro | author5 = Shinya Nomoto | author6 = Ryuji Tada | author7 = Hiroshi Kitazato | author8 = Naohiko Ohkouchi | title = Diazotrophic cyanobacteria as the major photoautotrophs during mid-Cretaceous oceanic anoxic events: Nitrogen and carbon isotopic evidence from sedimentary porphyrin | journal = Organic Geochemistry | volume = 39 | issue = 5 | pages = 532–549 | date = May 2008 | doi = 10.1016/j.orggeochem.2007.11.010 |bibcode = 2008OrGeo..39..532K }}
* {{cite book |first1=Neal L |last1=Larson |first2=Steven D |last2=Jorgensen |first3=Robert A |last3=Farrar |first4=Peter L |last4=Larson |title=Ammonites and the other Cephalopods of the Pierre Seaway |publisher=Geoscience Press |year=1997 }}
* {{cite web |last=Ogg |first=Jim |date=June 2004 |title=Overview of Global Boundary Stratotype Sections and Points (GSSP's) |archive-url=https://web.archive.org/web/20060716071827/http://www.stratigraphy.org/gssp.htm |url=http://www.stratigraphy.org/gssp.htm  |archive-date=16 July 2006 }}
* {{cite journal |last1=Ovechkina |first1=M.N. |last2=Alekseev |first2=A.S. |year=2005 |title=Quantitative changes of calcareous nannoflora in the Saratov region (Russian Platform) during the late Maastrichtian warming event |url=http://www.ucm.es/info/estratig/vol31/10ovek.pdf |journal=[[Journal of Iberian Geology]] |volume=31 |issue=1 |pages=149–165 |url-status=dead |archive-url=https://web.archive.org/web/20060824202146/http://www.ucm.es/info/estratig/vol31/10ovek.pdf |archive-date=August 24, 2006 }}
* {{cite book |author-link1=Alex Rasnitsyn |last1=Rasnitsyn |first1=A.P. |last2=Quicke |first2=D.L.J. |title=History of Insects |year=2002 |publisher=[[Kluwer Academic Publishers]] |isbn=978-1-4020-0026-3 }}—detailed coverage of various aspects of the evolutionary history of the insects.
* {{cite book |last1=Skinner |first1=Brian J. |first2=Stephen C. |last2=Porter |title=The Dynamic Earth: An Introduction to Physical Geology |url=https://archive.org/details/dynamicearthin00skin |url-access=registration |edition=3rd |location=New York |publisher=John Wiley & Sons |year=1995 |isbn=0-471-60618-9 }}
* {{cite book |last1=Stanley |first1=Steven M. |title=Earth System History |location=New York |publisher=W.H. Freeman and Company|year=1999 |isbn=0-7167-2882-6 }}
* {{Cite journal | last1 = Taylor | first1 = P. D. | last2 = Wilson | first2 = M. A. | doi = 10.1016/S0012-8252(02)00131-9 | title = Palaeoecology and evolution of marine hard substrate communities | journal = Earth-Science Reviews | volume = 62 | issue = 1 | pages = 1–103 | year = 2003 |bibcode = 2003ESRv...62....1T | url = http://doc.rero.ch/record/13828/files/PAL_E727.pdf }}

== External links ==
{{Commons category}}
{{Wiktionary}}
*[http://www.ucmp.berkeley.edu/mesozoic/cretaceous/cretaceous.html UCMP Berkeley Cretaceous page]
*[http://www.foraminifera.eu/querydb.php?period=Cretaceous&aktion=suche Cretaceous Microfossils: 180+ images of Foraminifera]
*[https://ghkclass.com/ghkC.html?cretaceous Cretaceous (chronostratigraphy scale)]
*{{Cite EB1911 |wstitle=Cretaceous System |volume=7 |pages=414–418 |short=1}}

{{Cretaceous Footer}}
{{Geological history|p|m|state=collapsed}}

{{Authority control}}

[[Category:Cretaceous| ]]
[[Category:Geological periods]]