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The Cretaceous as a separate period was first defined by a Belgian geologist Jean d ' Omalius d ' Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk ( calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths ), found in the upper Cretaceous of western Europe.
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Cretaceous and separate
All four groups survived into the Cretaceous, and three of those — the ceratosaurs, coelurosaurs, and allosaurs — survived to end of the period, where they were geographically separate, the ceratosaurs and allosaurs in Gondwana, and the coelurosaurs in Laurasia.
It was formerly believed that these two sites were two separate craters and that they formed a twin impact structure from a large-scale meteorite hit in the late Cretaceous.
Though not forming a separate branch together, such forms lasting from the late Jurassic to the end of the Cretaceous shared the common design of a small running herbivore that apparently was very successful.
Late Cretaceous elasmosaurids from the Western Interior of North America have few features that separate them and are morphologically primitive.
During the Early Cretaceous the location was a flood plain within a great rift valley that formed as Australia started to separate northward from Antarctica.
Cretaceous and period
These microfossils indicate the swamp was `` formed during the Lower Cretaceous period when dinosaurs were at their heyday and when the first flowering plants were just appearing.
The order is thought to have first diverged from other related monocots some 120-130 million years ago ( early in the Cretaceous period ), although given the difficulty in classifying the families involved, estimates are likely to be uncertain.
The Cretaceous (, ), derived from the Latin " creta " ( chalk ), usually abbreviated K for its German translation Kreide ( chalk ), is a geologic period and system from circa to million years ( Ma ) ago.
In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the Cenozoic era.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels and creating numerous shallow inland seas.
Geography of the Contiguous US in the late Cretaceous period
The Cretaceous is justly famous for its chalk ; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic.
Early marsupial mammals evolved in the Early Cretaceous, with true placentals emerging in the Late Cretaceous period.
Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded they faced growing competition from the adaptive radiation of birds, and by the end of the period only two highly specialized families remained.
Marine reptiles included ichthyosaurs in the early and middle of the Cretaceous ( becoming extinct during the late Cretaceous Cenomanian-Turonian anoxic event ), plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous.
There was a progressive decline in biodiversity during the Maastrichtian stage of the Cretaceous period prior to the suggested ecological crisis induced by events at the K – Pg boundary ( K – T boundary ).
The Cretaceous – Paleogene extinction event, often referred to as the Cretaceous – Tertiary extinction event, occurred approximately 65. 5 million years ago ( Ma ) at the end of the Maastrichtian age of the Cretaceous period.
The Deccan Traps formed between 60 and 68 million years ago, at the end of the Cretaceous period.
The most recent, the Cretaceous – Paleogene extinction event, which occurred approximately 65. 5 million years ago ( Ma ), was a large-scale mass extinction of animal and plant species in a geologically short period of time.
Primate evolution likely began in the late Cretaceous period.
Cretaceous and was
The seaway was receding as the climate cooled and sea levels subsided towards the end of the Cretaceous, exposing land that had previously been underwater.
The name Cretaceous was derived from Latin creta, meaning chalk.
The high eustatic sea level and warm climate of the Cretaceous meant a large area of the continents was covered by warm shallow seas.
The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the Cretaceous system consists for a major part of marine limestone, a rock type that is formed under warm, shallow marine circumstances.
Though Gondwana was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica and Australia rifted away from Africa ( though India and Madagascar remained attached to each other ); thus, the South Atlantic and Indian Oceans were newly formed.
At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged.
Although the first representatives of leafy trees and true grasses emerged in the Cretaceous, the flora was still dominated by conifers like Araucaria ( Here: Modern Araucaria araucana in Chile ).
File: Velociraptor dinoguy2. jpg | Up to 2 m-long Velociraptor was likely feathered and roamed the late Cretaceous.
The Cretaceous was also an important interval in the evolution of bioerosion, the production of borings and scrapings in rocks, hardgrounds and shells ( Taylor and Wilson, 2003 ).
File: TylosaurusDB2. jpg | Tylosaurus was the largest known mosasaur, carnivorous marine reptiles that emerged in the late Cretaceous.
Many researchers believe the extinction was more gradual, resulting from the sea level and climate changes already occurring during the late Cretaceous, and aggravated by impact events or increased volcanic activity.
Some sort of continental drift without expansion was proposed by Frank Bursley Taylor, who suggested in 1908 ( published in 1910 ) that the continents were dragged towards the equator by increased lunar gravity during the Cretaceous, thus forming the Himalayas and Alps on the southern faces.
It is estimated that Dioscoreales and its sister clade Pandanales split up around 121 millions of years ago during Early Cretaceous when the stem group was formed.
It lived during the Early Cretaceous, in China, where the first fossil was found in the Junggar Basin.
In 1933 the suggestion was made that the monster " bears a striking resemblance to the supposedly extinct plesiosaur ", a long-necked aquatic reptile that went extinct during the Cretaceous – Paleogene extinction event.
By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass was still dominated by cycad and ferns until after the Cretaceous – Paleogene extinction.
Quetzalcoatlus () was a pterodactyloid pterosaur known from the Late Cretaceous of North America ( Maastrichtian stage, about 68 – 65. 5 million years ago ), and one of the largest known flying animals of all time.
Cretaceous and first
The first representatives of many leafy trees, including figs, planes and magnolias, appeared in the Cretaceous.
The first radiation of the diatoms ( generally siliceous, rather than calcareous ) in the oceans occurred during the Cretaceous ; freshwater diatoms did not appear until the Miocene.
Angiosperms radiated sometime in the early Cretaceous, first in the tropics, but the even temperature gradient allowed them to spread toward the poles throughout the period.
They first appeared and diversified in the Late Cretaceous.
Its fossils first were found by Othniel Charles Marsh in 1870, in the Late Cretaceous Smoky Hill Chalk deposits of western Kansas.
The first monument consisted of a circular bank and ditch enclosure made of Late Cretaceous ( Santonian Age ) Seaford Chalk, ( 7 and 8 ), measuring about in diameter, with a large entrance to the north east and a smaller one to the south ( 14 ).
Vessels first evolved during the dry, low periods of the late Permian, in the horsetails, ferns and Selaginellales independently, and later appeared in the mid Cretaceous in angiosperms and gnetophytes.
Characiformes likely first diversified during the Cretaceous period, though fossils are poorly known.
The first radiometric ages from the Judith River Formation ( Upper Cretaceous ), Hill County, Montana.
The fossil record shows that monotremes have been present in Australia since the Early Cretaceous 145 – 99 MYA, and that marsupials and placental mammals date from the Eocene 56 – 34 MYA, when modern mammals first appeared in the fossil record.
The first amniotes are known from the early part of the Late Carboniferous, and during the Triassic counted among their number the earliest mammals, turtles, crocodiles ( lizards and birds appeared in the Jurassic, and snakes in the Cretaceous ), and a fourth Carboniferous group, the baphetids, which are thought to be related to temnospondyls, left no modern survivors.
The euechinoids, on the other hand, diversified into new lineages throughout the Jurassic and into the Cretaceous periods, and from them emerged the first irregular echinoids ( superorder Atelostomata ) during the early Jurassic, and later the other superorder ( Gnathostomata ) of irregular urchins, which evolved independently.
Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian ( circa 400 million years ago ) and became extinct at the close of the Cretaceous ( 65. 5 Ma ) along with the dinosaurs.
In the late Cretaceous the first continental collision took place as the northern part of the Apulian subplate collided with Europe.
The first seabirds evolved in the Cretaceous period, and modern seabird families emerged in the Paleogene.
They are first known to occur in the Cretaceous Period, the earliest being the Hesperornithiformes, like Hesperornis regalis, a flightless loon-like seabird that dove in a fashion similar to grebes and loons ( using its feet to move underwater ) but had a beak filled with sharp teeth.
One of the earliest known terrestrial ( land-dwelling ) gastropods is Maturipupa, which is found in the Coal Measures of the Carboniferous period in Europe, but relatives of the modern land snails are rare before the Cretaceous period, when the familiar Helix first appeared.
The first fossil examples of the family appear during the Cretaceous.
Eusuchia, a modern clade which includes the crown group Crocodilia, first appeared in the Lower Cretaceous of Europe.
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