Cretaceous Period

What happened during this time?

Biological

Flora

• 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

  • Marsileaceae diversify in the Aptian–Albian of the Early Cretaceous (De Benedetti et al. 2021)

  • Salviniaceae is first recorded in the Early Cretaceous, and diversify during the Campanian–Maastrichtian of the Late Cretaceous (De Benedetti et al. 2021)

Fauna

• New kinds of dinosaurs appear

  • First ceratopsian

  • First pachycepalosaurid dinosaurs 

• First fossils of many insect groups

  • Butterflies probably originated in the mid-Cretaceous (Kawahara et al. 2019) in North America as specialist on the bean family, Fabaceae (Kawahara et al. 2023) 

• Modern mammal groups arise

• Birds evolve from therapod lineage

• Extinction of non-avian dinosaurs and ammonites

Geophysical

• 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