Cretaceous Period

Origin of the flowering plants

The Cretaceous Period (145-66 Ma) is in the Mesozoic Era, occurring after the Jurassic Period, and before the Cenozoic Era. The Cretaceous Period is the last period in the Mesozoic Era.

Geologic Age

  • 145.0–66.0 Ma


Eon / Era/ Epoch

What happened during this time?



  • Increased northern and southern regional differences in floras.

    • First flowering plants appear on the landscape (~130 Ma)

    • By the Late Cretaceous, forests evolved to look similar to present-day forests, with oaks, hickories, and magnolias becoming common in North America

  • Ferns


  • New kinds of dinosaurs appear

    • First ceratopsian

    • First pachycepalosaurid dinosaurs

  • First fossils of many insect groups

  • Modern mammal groups arise

  • Birds evolve from therapod lineage

  • Extinction of non-avian dinosaurs and ammonites


  • Carbon dioxide level begin ~1,330 ppm and rise to over 2,000 ppm by the end of the Early Cretaceous. During the Late Cretaceous levels fall to ~1,000 ppm

  • Oxygen levels begin at ~20.5% and increase to ~22.5% by the end of the period

  • Pangaea rifting apart during Early Cretaceous; split in separate continents by the Late Cretaceous

    • Large-scale geographic isolation, causing a divergence in evolution of all land-based life for the two new land masses

    • Extensive new coastlines, and a corresponding increase in the available near-shore habitat.

  • Seasons grow more pronounced as the global climate became cooler

  • At end of the Cretaceous Period, an asteroid hits Earth in the Yucatan Peninsula, Mexico, forming what is today called the Chicxulub impact crater

    • Chicxulub bolide was an asteroid 6 miles in diameter, collodes with Earth between 66.03 - 66.04 Ma (Renne et al. 2013)

    • It has been estimated that half of the world's species went extinct at about this time, but no accurate species count exists for all groups of organisms

    • Some have argued that many of the species to go extinct did so before the impact, perhaps because of environmental changes occurring at this time