Editing Cretaceous (section)

{{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]].