Name and dating
When sustaining more older geological periods, a rock beds that define a Cretaceous time come swell identified, however a precise dates of the period's begin & prevent come uncertain by two or three million years. There are no groovy extinction or burst of diversity separated a Cretaceous period from either the Jurassic. Even so, a prevent of the time is virtually all sharply defined, existence positioned at an iridium-rich layer found worldwide that is believed to exist as associated by owning a Chicxulub impact crater in Yucatan and the Gulf of Mexico. This layer has been tightly dated at 65.Quint Ma. This bolide collision is probably responsible for the major, extensively-exposed Cretaceous-Tertiary extinction event. A Cretaceous period (from either Latin creta, for chalk) was named for the extensive beds of chalk (calcium carbonate deposited by the layers of marine invertebrates) found in the upper Cretaceous period of Britain and adjacent continental Europe.

Divisions

A Cretaceous period is unremarkably separated into Lower and Upper Cretaceous Epochs. A faunal stages from youngest to oldest come:

Paleogeography
In a period of a Cretaceous period, the late Paleozoic - early Mesozoic supercontinent of Pangea completed its breakup into present day continents, although their positions were substantially different at the instance. When a Atlantic Ocean widened and South America drifted westwards, Gondwana itself broke higher when Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached). Such active rifting upraised neat submarine range of mountains along a welts, raising eustatic sea levels worldwide. Northward of Africa a Tethys Sea continued to narrow. Inside the continents, a wide shallow sea advanced through central North America (the Western Interior Seaway) and then began to recede, allowing heavy marine deposits sandwiched between coal beds.

More significant Cretaceous exposures occur around Europe and China. In a area that is today India, massive lava beds known as the Deccan Traps were laid down in the super late Cretaceous period & early Paleocene. Climates were warmly, & possibly polar zone experienced there are no lasting ice.

Flora

Flowering plants first appeared, although they did non be predominant until touching a prevent of the time period (Campanian age). Their evolution aided per appearance of bees, in fact flowering plant & insects come a good case of reciprocal evolution. A foremost representatives of numbers of modern trees, including figs, planes and magnolias for example, come out in the Cretaceous period. At a equivalent period, a bit of earliest Mesozoic gymnosperms, like Conifers continued to thrive, although other taxa such as Bennettitales died out before a prevent of the time.

Fauna

Land animals

Ashore, mammals were a microscopic & however comparatively minor component of the fauna. A animal was dominated by archosaurian reptiles, especially dinosaurs, which were at their most diverse. Pterosaurs were common in a early & middle Cretaceous period period, however when a Cretaceous proceeded faced growing competition from either the adaptive radiation of birds, and per prevent of the time merely deuce extremely specialised families remained.

The fascinating glimpse of life in the Early Cretaceous is provided per Liaoning lagerstätte (Chaomidianzi formation) in Chinthe, in which a attractively preserved remains of a total of types of little dinosaurs, birds, & mammalian keep close at hand been uncovered. A coelurosaur dinosaurs found there represent the total of types of the class action maniraptora, which is transitional between dinosaurs & birds, and come remarkable for the presence of hair-capillary feathers.

When you took a Cretaceous period a insects began to diversify, and a oldest known ants, termites and butterflies appeared. Aphids, grasshoppers, and gall wasps appeared. An additional significant insect to develop was a eusocial bee, which was integral to the ecology and evolution of flowering plants.

Marine animals

In the seas, rays, modern sharks and teleosts became common. Marine reptilian involved ichthyosaurs in the early and middle of the Cretaceous period, plesiosaurs throughout the entire period of time, & mosasaurs in the late Cretaceous.

Baculites, a straight-shelled form of ammonite, flourished in the seas. A Hesperornithiformes were flightless, marine diving birds that swam like grebes. Globotruncanid Foraminifera thrived. A Cretaceous period likewise saw a 1st radiation of the diatoms in a oceans (freshwater diatoms did not come out until the Miocene).

Extinction
Independent article: Cretaceous-Tertiary extinction event

In the extinction event that defines the prevent of the Cretaceous period, the important total of mintage (~50%) & known families (~25%) disappeared. Plants were about unharmed, when marine parasites were hit a hardest. These include the prominent total (~95%) of types of planktic foraminifers (excepting the Globigerinida), an even battalion of Coccolithophores, all the ammonite and belemnite cephalopods, and entirely reef-forming rudist molluscs), when well as altogether marine reptilian except turtles and crocodiles. Dinosaurs are the best known hikers of the Cretaceous extinction. Dinosaurs that were unique to the super prevent of the period of time (like Tyrannosaurus rex, Triceratops, and Ankylosaurus) were wiped out. A go of the pterosaurs went extinct & a brobdingnagian majority of birds did too, including a Enantiornithes and Hesperornithiformes.