Ajay Kumar at 18:23, 28 August 2023

2023-08-28T18:23:48Z

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{{Short description|Subdivision of Cretaceous Period}}
{{Infobox geologic timespan
| name = Late/Upper Cretaceous
| color = Late Cretaceous
| time_start = 100.5
| time_end = 66.0
| image_map =
| caption_map =
| image_outcrop =
| caption_outcrop =
| image_art =
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| timeline = Cretaceous
| former_subdivisions =
| formerly_part_of =
| partially_contained_in =
| partially_contains =

| chrono_name = Late Cretaceous
| strat_name = Upper Cretaceous
| name_formality = Formal
| name_accept_date =
| alternate_spellings =
| synonym1 =
| synonym1_coined =
| synonym2 =
| synonym2_coined =
| synonym3 =
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| nicknames =
| former_names =
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| celestial_body = earth
| usage = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used = ICS Time Scale
| formerly_used_by =
| not_used_by =

| chrono_unit = Epoch
| strat_unit = Series
| proposed_by =
| timespan_formality = Formal
| lower_boundary_def = [[First appearance datum|FAD]] of the [[Foraminifera|Planktonic Foraminifer]] ''[[Rotalipora|Rotalipora globotruncanoides]]''
| lower_gssp_location = [[Mont Risoux]], [[Hautes-Alpes]], France
| lower_gssp_coords = {{Coord|44.3925|N|5.5119|E|display=inline}}
| lower_gssp_accept_date = 2002<ref>{{cite journal |last1=Kennedy |first1=W. |last2=Gale |first2=A. |last3=Lees |first3=J. |last4=Caron |first4=M. |title=The Global Boundary Stratotype Section and Point (GSSP) for the base of the Cenomanian Stage, Mont Risou, Hautes-Alpes, France |journal=Episodes |date=March 2004 |volume=27 |pages=21–32 |doi=10.18814/epiiugs/2004/v27i1/003 |url=https://stratigraphy.org/gssps/files/cenomanian.pdf |access-date=13 December 2020}}</ref>
| 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

| o2 =
| co2 =
| temp =
| sea_level =
}}
The '''Late Cretaceous''' (100.5–66 [[Year#SI prefix multipliers|Ma]]) is the younger of two [[epoch (geology)|epochs]] into which the [[Cretaceous]] [[geological period|Period]] is divided in the [[geologic time scale]]. [[Stratum|Rock strata]] from this epoch form the '''Upper Cretaceous''' [[series (stratigraphy)|Series]]. The Cretaceous is named after [[wikt:creta#Latin|''creta'']], the Latin word for the white [[limestone]] known as [[chalk]]. The chalk of northern France and the [[White Cliffs of Dover|white cliffs of south-eastern England]] date from the Cretaceous Period.<ref>
{{
Cite web
| title=Cretaceous Period {{!}} Definition, Climate, Dinosaurs, & Map
| url=https://www.britannica.com/science/Cretaceous-Period
| access-date=2022-07-25
| website=Encyclopedia Britannica
| language=en
}}
</ref>

==Climate==
During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident.<ref name="ageofdinosaurscretaceous"/> The [[tropics]] became restricted to equatorial regions and northern [[latitude]]s experienced markedly more seasonal climatic conditions.<ref name="ageofdinosaurscretaceous"/>

==Geography==
[[File:LateCretaceousMap.jpg|thumb|left|Late Cretaceous Map ([[Turonian]])]]
Due to [[plate tectonics]], the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The [[Western Interior Seaway]] divided North America into eastern and western halves; [[Appalachia (landmass)|Appalachia]] and [[Laramidia]].<ref name="ageofdinosaurscretaceous"/> India maintained a northward course towards Asia.<ref name="ageofdinosaurscretaceous"/> In the Southern Hemisphere, Australia and [[Antarctica]] seem to have remained connected and began to drift away from Africa and South America.<ref name="ageofdinosaurscretaceous">"Dinosaurs Ruled the World: Late Cretaceous Period." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. ''The Age of Dinosaurs''. Publications International, LTD. Pp. 103-104. {{ISBN|0-7853-0443-6}}.</ref> Europe was an island chain.<ref name="ageofdinosaurscretaceous"/> Populating some of these islands were endemic [[Insular dwarfism|dwarf]] dinosaur species.<ref name="ageofdinosaurscretaceous"/>

==Vertebrate fauna==

===Non-avian dinosaurs===
{{see also|Sauropod hiatus}}
In the Late Cretaceous, the [[Hadrosauridae|hadrosaurs]], [[Ankylosauria|ankylosaurs]], and [[ceratopsia]]ns experienced success in [[Asiamerica]] (Western North America and eastern Asia). [[Tyrannosaur]]s dominated the large predator niche in North America.<ref name="ageofdinosaurscretaceous"/> They were also present in Asia, although were usually smaller and more primitive than the North American varieties.<ref name="ageofdinosaurscretaceous"/> [[Pachycephalosaur]]s were also present in both North America and Asia.<ref name="ageofdinosaurscretaceous"/> [[Dromaeosauridae|Dromaeosaurids]] shared the same geographical distribution, and are well documented in both Mongolia and Western North America.<ref name="ageofdinosaurscretaceous"/> Additionally [[therizinosaur]]s (known previously as segnosaurs) appear to have been in North America and Asia. [[Gondwana]] held a very different dinosaurian fauna, with most predators being [[Abelisauridae|abelisaurids]] and [[Carcharodontosauridae|carcharodontosaurids]]; and [[titanosaur]]s being among the dominant herbivores.<ref name="ageofdinosaurscretaceous"/>
[[Spinosauridae|Spinosaurids]] were also present during this time.<ref>{{Cite journal|journal=Palaeontology |volume=44 |issue=2 |pages=305–323 |doi=10.1111/1475-4983.00181 |year=2001 |last1=Churcher |first1=C. S |title=A new species of Protopterus and a revision of Ceratodus humei (Dipnoi: Ceratodontiformes) from the Late Cretaceous Mut Formation of eastern Dakhleh Oasis, Western Desert of Egypt |last2=De Iuliis |first2=G |doi-access=free }}</ref>

===Birds===
Birds became increasingly common, diversifying in a variety of [[Enantiornithes|enantiornithe]] and [[Ornithurae|ornithurine]] forms. Early [[Neornithes]] such as ''[[Vegavis]]''<ref name="clarkeetal2005">{{cite journal | last1 = Clarke | first1 = J.A. | last2 = Tambussi | first2 = C.P. | last3 = Noriega | first3 = J.I. | last4 = Erickson | first4 = G.M. | last5 = Ketcham | first5 = R.A. | year = 2005 | title = Definitive fossil evidence for the extant avian radiation in the Cretaceous | journal = Nature | volume = 433 | issue = 7023| pages = 305–308 | doi = 10.1038/nature03150 | url = http://www.digimorph.org/specimens/Vegavis_iaai/nature03150.pdf | pmid=15662422| bibcode = 2005Natur.433..305C | s2cid = 4354309 }} [http://www.nature.com/nature/journal/v433/n7023/suppinfo/nature03150.html Supporting information]</ref> co-existed with forms as bizarre as ''[[Yungavolucris]]'' and ''[[Avisaurus]]''.<ref name="El-Brete-09">{{cite journal |author=Cyril A. Walker |author2=Gareth J. Dyke |name-list-style=amp |year=2009 |title=Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina) |url=http://www.ria.ie/RIA/files/40/40a4c454-eef2-4de0-922d-48ae0c42037f.pdf |journal=Irish Journal of Earth Sciences |volume=27 |pages=15–62 |doi=10.3318/IJES.2010.27.15 |s2cid=129573066 |url-status=dead |archive-url=https://web.archive.org/web/20120320093759/http://www.ria.ie/RIA/files/40/40a4c454-eef2-4de0-922d-48ae0c42037f.pdf |archive-date=2012-03-20 }}</ref> Though mostly small, marine [[Hesperornithes]] became relatively large and flightless, adapted to life in the open sea.<ref name=Brodavis>{{cite journal |author1=Larry D. Martin |author2=Evgeny N. Kurochkin |author3=Tim T. Tokaryk |year=2012 |title=A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia |journal=[[Palaeoworld]] |volume=21|doi=10.1016/j.palwor.2012.02.005 |pages=59–63}}</ref>

===Pterosaurs===
Though primarily represented by [[Azhdarchidae|azhdarchids]], other forms like [[Pteranodontidae|pteranodontids]], [[Tapejaridae|tapejarids]] (''[[Caiuajara]]'' and ''[[Bakonydraco]]''), [[Nyctosauridae|nyctosaurids]] and uncertain forms (''[[Piksi]]'', ''[[Navajodactylus]]'') are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species.<ref>{{cite journal |author=Prondvai |first=E. |last2=Bodor |first2=E. R. |last3=Ösi |first3=A. |year=2014 |title=Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity |url=http://real.mtak.hu/21860/1/Prondvai_et_al.2014_reposit1_u_110445.946242.pdf |journal=Paleobiology |volume=40 |issue=2 |pages=288–321 |doi=10.1666/13030 |s2cid=85673254 |archive-url=https://web.archive.org/web/20230720013538/http://real.mtak.hu/21860/1/Prondvai_et_al.2014_reposit1_u_110445.946242.pdf |archive-date=July 20, 2023}}</ref>

===Mammals===
Several old [[mammal]] groups began to disappear, with the last [[eutriconodont]]s occurring in the [[Campanian]] of [[North America]].<ref>{{cite journal | doi = 10.1139/z69-196 | volume=47 | issue=6 | title=Studies of Late Cretaceous vertebrates. III. A triconodont mammal from Alberta | year=1969 | journal=Canadian Journal of Zoology | pages=1253–1256 | author=Fox Richard C}}</ref> In the northern hemisphere, [[cimolodont]], [[multituberculates]], [[metatheria]]ns and [[eutherian]]s were the dominant mammals, with the former two groups being the most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of [[dryolestoid]]s, [[gondwanathere]]s and other multituberculates and basal [[eutherian]]s; [[monotreme]]s were presumably present, as was the last of the [[haramiyida]]ns, ''Avashishta''.

Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ([[Deltatheroida]]), to mollusc-eater ([[Stagodontidae]]), to [[herbivores]] (multituberculates, ''[[Schowalteria]]'', [[Zhelestidae]] and [[Mesungulatidae]]) to highly atypical cursorial forms ([[Zalambdalestidae]], [[Brandoniidae]]).

True [[placental]]s evolved only at the very end of the epoch; the same can be said for true [[marsupial]]s. Instead, nearly all known eutherian and metatherian fossils belong to other groups.
<ref>{{cite journal|doi=10.1111/brv.12242 | pmid=28075073 | title=Resolving the relationships of Paleocene placental mammals | year=2015 | journal=Biological Reviews | volume=92 | issue=1 | pages=521–550 | author=Halliday Thomas J. D.| url=http://discovery.ucl.ac.uk/1473028/1/Halliday_et_al-Biological_Reviews.pdf | pmc=6849585 }}</ref>

===Marine life===
In the seas, [[mosasaur]]s suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like [[Polycotylidae|polycotylid]] [[plesiosaur]]s (3 meters long) and huge long-necked [[Elasmosauridae|elasmosaurs]] (13 meters long) also diversified. These predators fed on the numerous [[teleost]] fishes, which in turn evolved into new advanced and modern forms ([[Neoteleostei]]). [[Ichthyosaur]]s and [[pliosaur]]s, on the other hand, became extinct during the [[Cenomanian-Turonian anoxic event]].

==Flora==
Near the end of the Cretaceous Period, [[flowering plant]]s diversified. In temperate regions, familiar plants like [[magnolia]]s, [[sassafras]], [[rose]]s, [[redwood]]s, and [[willow]]s could be found in abundance.<ref name="ageofdinosaurscretaceous"/>

==Cretaceous–Paleogene mass extinction discovery==
{{main|Cretaceous–Paleogene extinction event}}
The Cretaceous–Paleogene extinction event was a large-scale [[Extinction event|mass extinction]] of animal and plant species in a geologically short period of time, approximately {{Ma|Tertiary}} (Ma). It is widely known as the ''K–T extinction event'' and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the [[Cretaceous–Paleogene boundary]] (K–T boundary). ''K'' is the traditional abbreviation for the Cretaceous Period derived from the German name ''Kreidezeit'', and ''T'' is the abbreviation for the [[Tertiary]] Period (a historical term for the period of time now covered by the [[Paleogene]] and [[Neogene]] periods). The event marks the end of the [[Mesozoic]] Era and the beginning of the [[Cenozoic]] Era.<ref name="Fortey">{{cite book |author=Fortey R |title=Life: A Natural History of the First Four Billion Years of Life on Earth |publisher=Vintage |year=1999 |pages=238–260 |isbn=978-0375702617 }}</ref> "Tertiary" being no longer recognized as a formal time or rock unit by the [[International Commission on Stratigraphy]], the K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers.

[[File:Impact event.jpg|thumb|250px|Asteroids of only a few kilometers wide can release the energy of millions of nuclear weapons when colliding with planets ''(artist's impression)''.]]

Non-[[bird|avian]] [[dinosaur]] [[fossils]] are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event.<ref>{{cite journal |vauthors=Fastovsky DE, Sheehan PM |year=2005 |title=The extinction of the dinosaurs in North America |journal=GSA Today |volume=15 |issue=3 |pages=4–10 |doi=10.1130/1052-5173(2005)015<4:TEOTDI>2.0.CO;2 }}</ref> A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils, that is, fossils that have been eroded from their original locations then preserved in later [[sedimentary]] layers.<ref name="Sloan">{{cite journal |author1=Sloan RE |author2=Rigby K |author3=Van Valen LM |author4=Gabriel Diane |year=1986 |title=Gradual dinosaur extinction and simultaneous ungulate radiation in the Hell Creek formation |journal=Science |volume=232 |issue=4750 |pages=629–633 |doi= 10.1126/science.232.4750.629|pmid=17781415|bibcode = 1986Sci...232..629S |s2cid=31638639 }}</ref><ref name= "Fassett">{{cite conference|url=http://www.lpi.usra.edu/meetings/impact2000/pdf/3139.pdf |title=Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone San Juan Basin, New Mexico and Colorado, USA |vauthors=Fassett JE, Lucas SG, Zielinski RA, Budahn JR |conference=International Conference on Catastrophic Events and Mass Extinctions: Impacts and Beyond|date = 9–12 July 2000|location =Vienna, Austria |volume=1053 |pages=45–46 }}</ref><ref name ="Sullivan">{{cite conference|author=Sullivan RM |title=No Paleocene dinosaurs in the San Juan Basin, New Mexico |url=http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm |journal=Geological Society of America Rocky Mountain - 55th Annual Meeting |volume=35 |issue=5 |pages=15 |date = May 8, 2003 |archive-url =https://web.archive.org/web/20070617091343/http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm|archive-date = 17 June 2007}}</ref> [[Mosasaur]]s, [[plesiosaur]]s, [[pterosaur]]s and many [[species]] of plants and [[invertebrate]]s also became extinct. [[Mammals|Mammalian]] and bird [[clade]]s passed through the boundary with few extinctions, and [[evolutionary radiation]] from those [[Maastrichtian]] clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms.<ref name="MacLeod">{{cite journal|author=MacLeod N, Rawson PF, Forey PL, Banner FT, Boudagher-Fadel MK, Bown PR, Burnett JA, Chambers, P, Culver S, Evans SE, Jeffery C, Kaminski MA, Lord AR, Milner AC, Milner AR, Morris N, Owen E, Rosen BR, Smith AB, Taylor PD, Urquhart E, Young JR |title=The Cretaceous–Tertiary biotic transition |year=1997 |journal=Journal of the Geological Society |volume=154 |issue=2 |pages=265–292 |doi= 10.1144/gsjgs.154.2.0265 |bibcode= 1997JGSoc.154..265M |s2cid=129654916 }}</ref>

Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive [[impact event|asteroid impact]] that caused the [[Chicxulub crater]], in combination with increased [[volcano|volcanic activity]], such as that recorded in the [[Deccan Traps]], both of which have been firmly dated to the time of the extinction event. In theory, these events reduced sunlight and hindered [[photosynthesis]], leading to a massive disruption in Earth's [[ecology]]. A much smaller number of researchers believe the extinction was more gradual, resulting from slower changes in [[sea level]] or [[climate]].<ref name="MacLeod"/>

==See also==
* [[Flora and fauna of the Maastrichtian stage]]
* [[Hațeg Island]]

{{Portal bar|Geology|Paleontology}}

==References==
{{Reflist|20em}}

{{Cretaceous Footer}}
{{Geological history|p|m}}

[[Category:Late Cretaceous| ]]
[[Category:Cretaceous geochronology| Late]]
[[Category:Geological epochs]]

Late Cretaceous - Revision history

Ajay Kumar at 18:23, 28 August 2023