The Asterales order probably originated in the Cretaceous ( 145 – 65 Mya ) on the supercontinent Gondwana which broke up from 184 – 80 Mya, forming the area that is now Australia, South America, Africa, India and Antarctica.

Its chemical composition makes it difficult to match the amber to its producers – it is most similar to the resins produced by flowering plants ; however, there are no flowering plant fossils until the Cretaceous, and they were not common until the Upper Cretaceous.

Paleontologists regard birds as the only clade of dinosaurs to have survived the Cretaceous – Paleogene extinction event 65. 5 Ma ago.

The Cretaceous ended with a large mass extinction, the Cretaceous – Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out.

The end of the Cretaceous is defined by the K – Pg boundary, a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic Eras.

The impact of a meteorite or comet is today widely accepted as the main reason for the Cretaceous – Paleogene extinction event.

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 ).

Also known as the K – T extinction event, it is associated with a geological signature known variously as the K – T boundary, the Cretaceous – Paleogene boundary or the K – Pg boundary, usually a thin band of sedimentation visible wherever rocks of this age are exposed.

In the abbreviated versions of the Cretaceous – Paleogene boundary, the K is the traditional abbreviation for the Cretaceous Period derived from the German name Kreidezeit, the Pg is the abbreviation for the Paleogene Period, and T is the abbreviation for the Tertiary Period ( comprising the Paleogene and Neogene ).

With " Tertiary " being discouraged as a formal time or rock unit by the International Commission on Stratigraphy, the K – T extinction event is now called the Cretaceous – Paleogene ( or K – Pg ) extinction event by many researchers.

In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the Cenozoic era.

# REDIRECT Cretaceous – Paleogene extinction event

The era began in the wake of the Cretaceous – Paleogene extinction event ( K-Pg event ) at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs ( as well as other terrestrial and marine flora and fauna ) at the end of the Mesozoic.

* Cretaceous – Paleogene boundary ( K – T boundary )

* Cretaceous – Paleogene extinction event

Because of its magnitude, scientists formerly speculated that the gases released during the formation of the Deccan Traps played a role in the Cretaceous – Paleogene extinction event ( also known as the K-Pg extinction ), which included the extinction of the non-avian dinosaurs.

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.

# Cretaceous – Paleogene extinction event ( End Cretaceous, K-T extinction, or K-Pg extinction ): 65. 5 Ma at the Cretaceous. Maastrichtian-Paleogene. Danian transition interval.

No great extinction or burst of diversity separates the Cretaceous from the Jurassic.

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.

This plant extinction caused a major reshuffling of the dominant plant groups .< ref name =" autogenerated347 "> Photosynthesizing organisms, including phytoplankton and land plants, formed the foundation of the food chain in the late Cretaceous as they do today.

Approximately 35 % of echinoderm genera became extinct at the K – T boundary, although taxa that thrived in low-latitude, shallow-water environments during late Cretaceous had the highest extinction rate.

Researchers found that Cretaceous sites, prior to the extinction event, had rich plant and insect-feeding diversity.

Others have interpreted the fossil bearing rocks along Red Deer River in Alberta, Canada, as supporting a gradual extinction of non-avian dinosaurs ; during the last 10 million years of the Cretaceous layers there, the number of dinosaur species seems to have decreased from about 45 to about 12.

All major Cretaceous mammalian lineages, including monotremes ( egg-laying mammals ), multituberculates, marsupials and placentals, dryolestoideans, and gondwanatheres survived the K – Pg extinction event, although they suffered losses.

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.

The loons were formerly often considered to be the most ancient of the northern hemisphere bird families ; this idea grew basically out of the perceived similarity of shape and ( probably ) habits between loons and the entirely unrelated extinct Cretaceous order Hesperornithiformes.

Much larger forms are found in the later rocks of the upper part of the Jurassic and the lower part of the Cretaceous, such as Titanites from the Portland Stone of Jurassic of southern England, which is often 53 centimetres ( 2 feet ) in diameter, and Parapuzosia seppenradensis of the Cretaceous period of Germany, which is one of the largest known ammonites, sometimes reaching 2 metres ( 6. 5 feet ) in diameter.

As the Cretaceous chalk layer in southern England is typically tilted, chalk downland formations often have a marked scarp slope on one side, which is very steep, and a dip slope on the other, which is much shallower.

According to the famous DNA hybridization study into avian phylogenetic relationships by Sibley and Ahlquist, the split of the Procellariiformes into the four families occurred around 30 million years ago ; a fossil bone often attributed to the order, described as the genus Tytthostonyx, has been found in rocks dating around the Cretaceous – Paleogene boundary ( 70-60 mya ), but the remains are too incomplete for placement within the Procellariiformes to be certain.

They consist of over of sedimentary rock strata laid down before mountain-building began: the predominantly marine and near-shore sedimentary layers range from the Cambrian through the Lower Cretaceous, and are often rich in fossils.

Belemnoids were numerous during the Jurassic and Cretaceous periods, and their fossils are abundant in Mesozoic marine rocks, often accompanying their cousins the ammonites.

The marine rocks of the Jurassic period in Britain often yield specimens of Cenoceras, and nautiloids such as Eutrephoceras are also found in the Pierre Shale formation of the Cretaceous period in the north-central United States.

The Chalk Group ( often just called the Chalk ) is the lithostratigraphic unit ( a certain number of rock strata ) which contains the late Cretaceous limestone succession in southern and eastern England.

Baculites and related Cretaceous straight ammonite cephalopods are often confused with the superficially similar orthocerid nautiloid cephalopods.

Formerly referred to as Ichthyornis lentus, Graculavus lentus or Pedioecetes lentus, its partial left tarsometatarsus was found in the Late Cretaceous Austin Chalk near Fort McKinney, Texas.

The oldest known fossils attributed to the genus, however, are of leaves from Cretaceous Alaska, referred to the species, T. borealis

Fourteen species have since been referred to Titanosaurus, which distribute the genus across Argentina, Europe, Madagascar, India and Laos and throughout 60 million years of the Cretaceous Period.

The term originally referred to the region underlain by a thin layer of rich, black topsoil developed atop the chalk of the Selma Group, a geologic unit dating to the Cretaceous Period.

Additionally, all six turtle families in existence at the end of the Cretaceous survived into the Tertiary and are represented by current species.

The earliest carnivorous mammal is considered to be the Cimolestes that existed during the Late Cretaceous and Tertiary Periods in North America about 65 million years ago.

For example, the discovery by Luis Alvarez and Walter Alvarez of an iridium-rich layer at the Cretaceous – Tertiary boundary made asteroid impact and volcanism the most favored explanations for the Cretaceous – Paleogene extinction event.

Crystalline rocks crop out at several capes ; Cretaceous limestones, containing an abundant and specific fauna of gigantic ammonites, occur at Dui on the west coast ; and Tertiary conglomerates, sandstones, marls and clays, folded by subsequent upheavals, are found in many parts of the island.

The batholith is overlain by dacite from the Tertiary Period ( roughly 65 million to 1. 8 million years ago ) and andesite from the late Cretaceous.

Liriodendron has been reported as fossils from the late Cretaceous and early Tertiary of North America and central Asia.

From the Early Cretaceous and into Late Cretaceous times the Harz was uplifted in a single block by tectonic movements and, particularly during the Tertiary period, the younger overlying strata were eroded and the underlying base rock left standing as low mountains.

Recent hypotheses based on total-evidence approach analysis place the origin of ticks in the Cretaceous () with most of the evolution and dispersal occurring during the Tertiary ().

Much of the record of this deformation has been overridden by Tertiary age structures and the zone of Cretaceous dextral thrust faulting appears to have been widespread.

The fall line marks the geologic boundary of hard metamorphosed terrain — the product of the Taconic orogeny — and the sandy, relatively flat outwash plain of the upper continental shelf, formed of unconsolidated Cretaceous and Tertiary sediments.

The fossil record begins in the early Cretaceous and continues throughout the Tertiary.

As much as 5000 m of Cretaceous and Tertiary sediments filled these orogenically defined basins.

A variety of Cretaceous and Tertiary fossil organisms exist in abundance.

Following the ending of rifting in the Late Cretaceous to the early Tertiary, the Big Bend area was subjected to the Laramide orogeny.

His contributions to geological science comprise memoirs on the Jurassic, Cretaceous and Tertiary Strata of the Paris Basin and of Northern France, and other papers relating to the antiquity of man, and to the question of his co-existence with extinct mammalia.

After being periodically submerged during Jurassic and Cretaceous periods, the region finally became land in Tertiary period.

The sycamore made up a large part of the forests of Greenland and Arctic America during the Cretaceous and Tertiary periods.