Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Cretaceous
Contents
Overview
Terrestrial Life through the Cretaceous
Life in the Cretaceous Seas
Extinction of the Dinosaurs
Continents and Greenhouse Climates
Evidence
Leaf related to the gooseberry family
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sample
Tyrannosaurus rex
Triceratops prorsus
Edmontosaurus annectens
Mosasaurs
Plesiosaurs
Pterosaurs
Ferns
Cycads
Bennettitalean trunks
Coccolithophores
Ammonites
Belemnites
Inoceramids
Rudistids
Diatoms
Foraminifera
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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OVERVIEW
Cretaceous 146–65.5 mya
Defining Characteristics:
  • • extinction of the dinosaurs
  • • first appearance and diversification of flowering plants
  • • extreme global warming
  • • Map of the Cretaceous World
Secondary Characteristics:
  • • oldest known specimens of termites, ants, and bees
  • • diversification of birds and many new insect groups
  • • new kinds of dinosaurs

The name Terrain crétacé (“chalky terrain”) was coined in 1822 by Belgian geologist D'Omalius d'Halloy to refer to the chalk deposits of the Paris Basin, France. Later the name Cretaceous (“chalk-bearing,” from the Latin word creta, meaning “chalk”) came to be used for the many chalk deposits around the world that were formed during this age. One of the most famous examples is the White Cliffs of Dover, England. Such chalks formed from the bodies of billions of single-celled marine algae called coccolithophores. The coccolithophores lived in the sunny surface waters of the ocean, but after death their shells or scales sank to the bottom where they accumulated, were buried, and were compressed to form chalk. Coccolithophores are still important organisms in the oceans today.

The world of the Cretaceous Period (65.5–146 million years ago) brought significant changes to life and to Earth itself. Before this time period, during the Jurassic, animal life on land was dominated by dinosaurs. Some of the dominant plants included ferns, cycads, seed ferns, ginkgos, and conifers. In the seas, marine reptiles (ichthyosaurs and plesiosaurs), sharks, and ammonites were common. Most of these life forms still dominated the Cretaceous world, although new types of dinosaurs and plants also appeared. All of Earth’s landmasses had been clumped together into one huge supercontinent called Pangea, but this had begun to break apart during the Triassic, and seaways had begun to invade Pangea during the Jurassic. By the Cretaceous this process was well under way, making Earth’s climate more equable and greatly affecting both plants and animals.





Overview | Terrestrial Life through the Cretaceous | Life in the Cretaceous Seas
Extinction of the Dinosaurs | Shifting Continents and Greenhouse Climates



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