Cretaceous Period FACT FILE
The Cretaceous (/krɨˈteɪʃəs/, krə-TAY-shəs), derived from the Latin "creta" (chalk), usually abbreviated K for its German translation Kreide (chalk), is a geologic period and system from circa 145 ± 4 to 66 million years (Ma) ago
*Based on 'The Geologic Time Scale 2012' by F M Gradstein, J G Ogg, M Schmitz & G Ogg (2012), with additions. Credit: British Geological Survey
The start of the period is marked by palaeontological markers which suggest a marine extinction event.
The Cretaceous ended with the most famous mass extinction in history - the one that killed off most of the dinosaurs (not the birds).
There was no great, global extinction or massive radiation of species separated the Cretaceous from the Jurassic Period. Dinosaurs continued to inhabit the forests of ferns, cycads, and conifers. Ammonites, belemnites, other molluscs, and fish were hunted by marine reptiles, and pterosaurs and early birds took to the skies. However, it was in the Cretaceous Period that the evolution of many lifeforms that would go on to play key roles in the coming Cenozoic occured.
It was a relatively warm period with no ice caps at the poles. Southern England and the midwest of the USA was underwater as sea levels reached their highest levels in geologic history during this time.
The Atlantic Ocean grew much wider as North and South America drew apart from Europe and Africa. The Indian Ocean was formed at this time, and the island that was India began its journey north towards Asia.
The BBC Nature website has a very good section on the Cretaceous.
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