Mount Lycabettus, also known as Lycabettos, Lykabettos or Lykavittos (, ), is a Cretaceous limestone hill in Athens, Greece.

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 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.

In older literature the Cretaceous is sometimes divided into three series: Neocomian ( lower / early ), Gallic ( middle ) and Senonian ( upper / late ).

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.

Image: DiscoscaphitesirisCretaceous. jpg | The ammonite Discoscaphites iris, Owl Creek Formation ( Upper Cretaceous ), Ripley, Mississippi.

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.

The Carinatae are, in phylogenetic taxonomy, the last common ancestor of the Neornithes ( modern birds ) and Ichthyornis ( an extinct seabird of the Cretaceous ), and all its descendants.

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.

The upper ( Cretaceous ) boundary is set at the Cretaceous-Tertiary ( KT ) extinction event ( now more accurately called the Cretaceous – Paleogene ( or K – Pg ) extinction event ), which may have been caused by the impactor that created Chicxulub Crater on the Yucatán Peninsula.

Because obsidian is metastable at the Earth's surface ( over time the glass becomes fine-grained mineral crystals ), no obsidian has been found that is older than Cretaceous age.

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.

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 ).

In Europe, some of the best toolmaking flint has come from Belgium ( Obourg, flint mines of Spiennes ), the coastal chalks of the English Channel, the Paris Basin, Thy in Jutland ( flint mine at Hov ), the Sennonian deposits of Rügen, Grimes Graves in England, the Upper Cretaceous chalk formation of Dobruja and the lower Danube ( Balkan flint ), the Cenomanian chalky marl formation of the Moldavian Plateau ( Miorcani flint ) and the Jurassic deposits of the Kraków area and Krzemionki in Poland.

Some evidence, such as the displacement of siliceous sponges from the shelves, suggests that this takeover began in the Cretaceous ( 146 Ma to 65 Ma ), while evidence from radiolarians suggests " take-over " did not begin until the Cenozoic ( 65 Ma to present ).< ref name = harper75 > The expansion of grassland biomes and the evolutionary radiation of grasses during the Miocene is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this has promoted the diatoms during the Cenozoic era.

The first radiometric ages from the Judith River Formation ( Upper Cretaceous ), Hill County, Montana.

The name Cretaceous was derived from Latin creta, meaning chalk.

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 ).

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 ).

However, small dinosaur fossils ( teeth, bits of bone ) found after the Cretaceous – Paleogene boundary are likely to be derived fossils washed out of eroded Mesozoic deposits, or remains of dinosaurs that died in the Cretaceous – Paleogene extinction event that were later washed into a lake or the sea.

Sinornithosaurus ( derived from a combination of Latin and Greek, meaning ' Chinese bird-lizard ') is a genus of feathered dromaeosaurid dinosaur from the early Cretaceous Period ( early Aptian ) of the Yixian Formation in what is now China.

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.

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

In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast.

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.

Famous formations from North America include the rich marine fossils of Kansas's Smoky Hill Chalk Member and the terrestrial fauna of the late Cretaceous Hell Creek Formation.

Rafting by ice of stones into marine environments occurred during much of the Cretaceous but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia.

Warm-adapted plant fossils are known from localities as far north as Alaska and Greenland, while dinosaur fossils have been found within 15 degrees of the Cretaceous south pole.

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.

File: Kronosaurus hunt1DB. jpg | A scene from the early Cretaceous: a Woolungasaurus is attacked by a Kronosaurus.

File: The fossils from Cretaceous age found in Lebanon. jpg | A plate with Nematonotus sp.

Image: Cretaceous_hardground. jpg | Cretaceous hardground from Texas with encrusting oysters and borings.

Image: RudistCretaceousUAE. jpg | Rudist bivalves from the Cretaceous of the Omani Mountains, United Arab Emirates.

Image: InoceramusCretaceousSouthDakota. jpg | Inoceramus from the Cretaceous of South Dakota.

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.

Approximately 46 % of diatom species survived the transition from the Cretaceous to the Upper Paleocene.

Rudist bivalves from the Late Cretaceous of the Omani Mountains, United Arab Emirates.

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.

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.

The Cretaceous is justly famous for its chalk ; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic.

The ridge is formed of oceanic sedimentary rock from the Late Cretaceous, and contains a soft chalk and a hard flint.

Hunstanton is notable for its stratified, fossiliferous cliffs: lower reddish limestone, known as ' red chalk ', which was laid down during the Lower Cretaceous Epoch and is topped by a white chalk layer from the Upper Cretaceous Epoch. The stratified red chalk limestone and white chalk cliff s on the beach at Old Hunstanton.

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.

The chalk was formed in the Late Cretaceous period, between 65 and 100 million years ago, when the area was under the sea.