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The Late Cretaceous
Cretaceous
(100.5–66 Ma) is the younger of two epochs into which the Cretaceous
Cretaceous
period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous
Cretaceous
series. The Cretaceous
Cretaceous
is named after the white limestone known as chalk which occurs widely in northern France and is seen in the white cliffs of south-eastern England, and which dates from this time.

Contents

1 Climate 2 Geography 3 Vertebrate fauna

3.1 Dinosaurs 3.2 Pterosaurs 3.3 Mammals 3.4 Marine life

4 Flora 5 Cretaceous– Paleogene mass extinction 6 See also 7 References

Climate[edit] During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident.[2] The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions.[2] Geography[edit] Due to plate tectonics, the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America
North America
into eastern and western halves; Appalachia and Laramidia.[2] India maintained a northward course towards Asia.[2] In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America.[2] Europe was an island chain.[2] Populating some of these islands were endemic dwarf dinosaur species.[2] Vertebrate fauna[edit] Dinosaurs[edit] In the Late Cretaceous, the hadrosaurs, ankylosaurs, and ceratopsians experienced success in Asiamerica (Western North America
North America
and eastern Asia). Tyrannosaurs dominated the large predator niche in North America.[2] They were also present in Asia, although were usually smaller and more primitive than the North American varieties.[2] Pachycephalosaurs were also present in both North America
North America
and Asia.[2] Dromaeosaurs shared the same geographical distribution, and are well documented in both Mongolia and Western North America.[2] Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America
North America
and Asia. Gondwana
Gondwana
held a very different dinosaurian fauna, with most predators being abelisaurs and carcharodontosaurs; and titanosaurs being among the dominant herbivores.[2] Spinosaurids were also present during this time. Birds became increasingly common and diverse, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes
Neornithes
such as Vegavis
Vegavis
co-existed with forms as bizarre as Yungavolucris
Yungavolucris
and Avisaurus. Though mostly small, marine Hesperornithes
Hesperornithes
became relatively large and flightless, adapted to life in the open sea. Pterosaurs[edit] Though primarily represented by azhdarchids, other forms like pteranodontids, tapejarids ( Caiuajara
Caiuajara
and Bakonydraco), 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.[3] Mammals[edit] Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian
Campanian
of North America.[4] In the northern hemisphere, cimolodont, multituberculates, metatherians and eutherians 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 dryolestoids, gondwanatheres and other multituberculates and basal eutherians; monotremes were presumably present, as was the last of the haramiyidans, 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). True placentals only evolved at the very end of the epoch; the same can be said for true marsupials. Instead, nearly all known eutherian and metatherian fossils belong to other groups. [5] Marine life[edit] In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and giant-penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked 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). Ichthyosaurs and pliosaurs, on the other hand, became extinct during the Cenomanian- Turonian
Turonian
anoxic event. Flora[edit] Near the end of the Cretaceous
Cretaceous
Period, flowering plants diversified. In temperate regions, familiar plants like magnolias, sassafras, roses, redwoods, and willows could be found in abundance.[2] Cretaceous– Paleogene mass extinction[edit] Main article: Cretaceous– Paleogene extinction event The Cretaceous– Paleogene extinction event was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66 million years ago (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
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
Neogene
periods). The event marks the end of the Mesozoic
Mesozoic
Era and the beginning of the Cenozoic
Cenozoic
Era.[6] "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. Non-avian dinosaur fossils are only found below the Cretaceous– Paleogene boundary and became extinct immediately before or during the event.[7] 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.[8][9][10] Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades 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.[11] Scientists have hypothesized that the Cretaceous–Paleogene extinctions were caused by one or more catastrophic events such as massive asteroid impacts or increased volcanic activity. Several impact craters and massive volcanic activity in the Deccan traps
Deccan traps
have been dated to the approximate time of the extinction event. These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology. Other researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate.[11] See also[edit]

Flora and fauna of the Maastrichtian
Maastrichtian
stage

Geology portal Paleontology portal Time portal

References[edit]

^ http://www.stratigraphy.org/index.php/ics-chart-timescale ^ a b c d e f g h i j k l m "Dinosaurs Ruled the World: Late Cretaceous
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. ^ Prondvai E., Bodor E. R., Ösi A. (2014). "Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity". Paleobiology. 40: 288–321. CS1 maint: Multiple names: authors list (link) ^ Fox Richard C (1969). "Studies of Late Cretaceous
Cretaceous
vertebrates. III. A triconodont mammal from Alberta". Canadian Journal of Zoology. 47: 1253–1256. doi:10.1139/z69-196.  ^ Halliday Thomas J. D. (2015). "Resolving the relationships of Paleocene
Paleocene
placental mammals". Biological Reviews. doi:10.1111/brv.12242.  ^ Fortey R (1999). Life: A Natural History of the First Four Billion Years of Life on Earth. Vintage. pp. 238–260. ISBN 978-0375702617.  ^ Fastovsky DE, Sheehan PM (2005). "The extinction of the dinosaurs in North America". GSA Today. 15 (3): 4–10. doi:10.1130/1052-5173(2005)015<4:TEOTDI>2.0.CO;2. Archived from the original on 2011-12-09. Retrieved 2007-05-18.  ^ Sloan RE; Rigby K; Van Valen LM; Gabriel Diane (1986). "Gradual dinosaur extinction and simultaneous ungulate radiation in the Hell Creek formation". Science. 232 (4750): 629–633. Bibcode:1986Sci...232..629S. doi:10.1126/science.232.4750.629. PMID 17781415. Retrieved 2007-05-18.  ^ Fassett JE, Lucas SG, Zielinski RA, Budahn JR (2001). "Compelling new evidence for Paleocene
Paleocene
dinosaurs in the Ojo Alamo Sandstone San Juan Basin, New Mexico and Colorado, USA" (PDF). International Conference on Catastrophic Events and Mass Extinctions: Impacts and Beyond, 9–12 July 2000, Vienna, Austria. 1053: 45–46. Retrieved 2007-05-18.  ^ Sullivan RM (2003). "No Paleocene
Paleocene
dinosaurs in the San Juan Basin, New Mexico". Geological Society of America Abstracts with Programs. 35 (5): 15. Retrieved 2007-07-02.  ^ a b 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 (1997). "The Cretaceous– Tertiary biotic transition". Journal of the Geological Society. 154 (2): 265–292. doi:10.1144/gsjgs.154.2.0265. Archived from the original on 2013-05-25. CS1 maint: Multiple names: authors list (link)

v t e

Cretaceous
Cretaceous
Period

Lower/Early Cretaceous Upper/Late Cretaceous

Berriasian Valanginian Hauterivian Barremian Aptian Albian

Cenomanian Turonian Coniacian Santonian Campanian Maastrichtian

v t e

Geologic history of Earth

Cenozoic
Cenozoic
era¹ (present–66.0 Mya)

Quaternary
Quaternary
(present–2.588 Mya)

Holocene
Holocene
(present–11.784 kya) Pleistocene
Pleistocene
(11.784 kya–2.588 Mya)

Neogene
Neogene
(2.588–23.03 Mya)

Pliocene
Pliocene
(2.588–5.333 Mya) Miocene
Miocene
(5.333–23.03 Mya)

Paleogene (23.03–66.0 Mya)

Oligocene
Oligocene
(23.03–33.9 Mya) Eocene
Eocene
(33.9–56.0 Mya) Paleocene
Paleocene
(56.0–66.0 Mya)

Mesozoic
Mesozoic
era¹ (66.0–251.902 Mya)

Cretaceous
Cretaceous
(66.0–145.0 Mya)

Late (66.0–100.5 Mya) Early (100.5–145.0 Mya)

Jurassic
Jurassic
(145.0–201.3 Mya)

Late (145.0–163.5 Mya) Middle (163.5–174.1 Mya) Early (174.1–201.3 Mya)

Triassic
Triassic
(201.3–251.902 Mya)

Late (201.3–237 Mya) Middle (237–247.2 Mya) Early (247.2–251.902 Mya)

Paleozoic
Paleozoic
era¹ (251.902–541.0 Mya)

Permian
Permian
(251.902–298.9 Mya)

Lopingian
Lopingian
(251.902–259.8 Mya) Guadalupian
Guadalupian
(259.8–272.3 Mya) Cisuralian
Cisuralian
(272.3–298.9 Mya)

Carboniferous
Carboniferous
(298.9–358.9 Mya)

Pennsylvanian (298.9–323.2 Mya) Mississippian (323.2–358.9 Mya)

Devonian
Devonian
(358.9–419.2 Mya)

Late (358.9–382.7 Mya) Middle (382.7–393.3 Mya) Early (393.3–419.2 Mya)

Silurian
Silurian
(419.2–443.8 Mya)

Pridoli (419.2–423.0 Mya) Ludlow (423.0–427.4 Mya) Wenlock (427.4–433.4 Mya) Llandovery (433.4–443.8 Mya)

Ordovician
Ordovician
(443.8–485.4 Mya)

Late (443.8–458.4 Mya) Middle (458.4–470.0 Mya) Early (470.0–485.4 Mya)

Cambrian
Cambrian
(485.4–541.0 Mya)

Furongian (485.4–497 Mya) Series 3 (497–509 Mya) Series 2 (509–521 Mya) Terreneuvian
Terreneuvian
(521–541.0 Mya)

Proterozoic
Proterozoic
eon² (541.0 Mya–2.5 Gya)

Neoproterozoic era (541.0 Mya–1 Gya)

Ediacaran
Ediacaran
(541.0-~635 Mya) Cryogenian (~635-~720 Mya) Tonian (~720 Mya-1 Gya)

Mesoproterozoic era (1–1.6 Gya)

Stenian (1-1.2 Gya) Ectasian (1.2-1.4 Gya) Calymmian (1.4-1.6 Gya)

Paleoproterozoic era (1.6–2.5 Gya)

Statherian (1.6-1.8 Gya) Orosirian
Orosirian
(1.8-2.05 Gya) Rhyacian (2.05-2.3 Gya) Siderian
Siderian
(2.3-2.5 Gya)

Archean
Archean
eon² (2.5–4 Gya)

Eras

Neoarchean (2.5–2.8 Gya) Mesoarchean (2.8–3.2 Gya) Paleoarchean
Paleoarchean
(3.2–3.6 Gya) Eoarchean
Eoarchean
(3.6–4 Gya)

Hadean
Hadean
eon² (4–4.6 Gya)

 

 

kya = thousands years ago. Mya = millions years ago. Gya = billions years ago.¹ = Phanerozoic
Phanerozoic
eon. ² = Precambrian
Precambrian
supereon. Source: (2017/02). International Commission on Stratigraphy. Retrieved 13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units USGS Retrie

.