The Cretaceous was the last and longest period of the Mesozoic, with a duration of 79 million years. It was established by Jean d'Omalius d'Halloy, a Belgian geologist, based on chalky rocks in Western Europe, named after the Latin word "creta" (chalk).

Paleogeography

By the end of the Cretaceous, the continents started to resemble their current, familiar-for-us shapes. Gondwana broke up. South America, Antarctica, and Australia migrated away from Africa, opening up the South Atlantic Ocean and expanding the Indian Ocean. Only the Deccan (Indian Peninsula) had not yet merged with Asia, and Australia was still connected to Antarctica.

Climate

The Cretaceous was warm, with little temperature variance between the equator and poles. Cold spells were brief, with the sea levels reaching the highest levels ever recorded in the Phanerozoic.

Life on Earth

Marine vertebrates

Vertebrates thrived in the seas. Shark species were very numerous, while other modern fish groups, like sturgeons, appeared. Cretaceous seas were still ruled by reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs.

Kings of the sky

All modern birds belong to the group Euornithes ("true birds"). Hovewer, the Cretaceous sky and land were also populated by animals related to true birds. Some resembled modern birds, while others were completely different and unique. By the end of the Cretaceous, that diversity had disappeared. Numerous Euornithes died out - the modern birds come from a few descendants that survived the mass extinction.

The skies were full of reptiles - pterosaurs. At the time, they were kings of the skies, being the largest animals that have ever taken to the air. The largest known pterosaur had a 10-metre wingspan.

Diversity of dinosaurs

The Pangea breaking up forced dinosaurs to split into isolated populations, leading to strong diversification and leading to appearance of groups characteristic for each continent. Most sauropods died at the beginning of the Cretaceous, those that survived reached unprecedented sizes.

Flower revolution

The oldest fossils of flowering plants (angiosperms) come from the Cretaceous rocks. Flowering was a novel way of reproducing in which plants develop a symbiosis with insects to disperse pollen in exchange for sweet nectar. This strategy proved to be extremely effective, as angiosperms today dominate the world of plants.

The K-Pg extinction

About 66 million years ago, another mass extinction took place. This catastrophic event had an impact on all ecosystems and taxa globally. The most widely accepted cause was a bolide hitting the Yucatan Peninsula and extensive volcanism on the Indian Peninsula.

Do you know…

In the Cretaceous, certain ammonites, like Didymoceras, created shells in unusual shapes