Cretaceous Period
Geologic Age
145.0–66.0 Ma
Subdivisions
Late Cretaceous: 100.5–66.0 Ma
Maastrichtian: 72.1±0.2–66.0 Ma
Campanian: 83.6±0.2–72.1±0.2 Ma
Santonian: 86.3±0.5–83.6±0.2 Ma
Coniacian: 89.8±0.3–86.3±0.5 Ma
Turonian: 93.9–89.8±0.3 Ma
Cenomanian: 100.5–93.9 Ma
Early Cretaceous: 145.0–100.5 Ma
Albian: 113.0–100.5 Ma
Aptain: 125.0–113.0 Ma
Barremian: 129.4–125.0 Ma
Hauterivian: 132.9–129.4 Ma
Valanginian: 139.8–132.9 Ma
Berriasian: 145.0–139.8 Ma
Eon / Era/ Epoch
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
