HOME
TheInfoList



The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous geological period is divided in the
geologic time scale The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth sciences, Earth scientists to describe t ...
.
Rock strata (Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is ...
from this epoch form the Upper Cretaceous series. The Cretaceous is named after the white
limestone Limestone is a common type of carbonate rock, carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science), crystal forms of calcium carbonate (). Limestone form ...
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.


Climate

During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. The
tropics The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S; these latitudes correspond to the ...
became restricted to equatorial regions and northern
latitude In geography, latitude is a geographic coordinate that specifies the north– south position of a point on the Earth's surface. Latitude is an angle (defined below) which ranges from 0° at the Equator to 90° (North or South) at the poles. L ...
s experienced markedly more seasonal climatic conditions.


Geography

Due to
plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτον ...
, 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 and Laramidia. India maintained a northward course towards Asia. In the Southern Hemisphere, Australia and
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oce ...

Antarctica
seem to have remained connected and began to drift away from Africa and South America."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. . Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species.


Vertebrate fauna


Non-Avian Dinosaurs

In the Late Cretaceous, the hadrosaurs, Ankylosauria, ankylosaurs, and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated the large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than the North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurs shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held a very different dinosaurian fauna, with most predators being abelisaurs and Carcharodontosauridae, carcharodontosaurs; and titanosaurs being among the dominant herbivores. Spinosauridae, Spinosaurids were also present during this time.


Birds

Birds became increasingly common, diversifying in a variety of Enantiornithes, enantiornithe and Ornithurae, ornithurine forms. Early Neornithes such as ''Vegavis'' co-existed with forms as bizarre as ''Yungavolucris'' and ''Avisaurus''. Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in the open sea.


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.


Mammals

Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America. 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) to highly atypical cursorial forms (Zalambdalestidae, Brandoniidae). 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.


Marine life

In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and giant-penguin-like Polycotylidae, polycotylid plesiosaurs (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). Ichthyosaurs and pliosaurs, on the other hand, became extinct during the Cenomanian-Turonian anoxic event.


Flora

Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias, sassafras, roses, redwoods, and willows could be found in abundance.


Cretaceous–Paleogene mass extinction

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). 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. "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-bird, avian dinosaur fossils are only found below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. 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. Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct. Mammals, 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. 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.


See also

* Flora and fauna of the Maastrichtian stage * Hațeg Island


References

{{Geological history, p, m Late Cretaceous, Cretaceous geochronology, Late Geological epochs tr:Geç Kretase