# Late Cretaceous
The **Late Cretaceous** is the second and younger epoch of the Cretaceous Period, spanning from 100.5 million years ago to 66 million years ago and ending with the Cretaceous–[Paleogene](https://www.edgepedia.org/paleogene) (K–Pg) mass extinction that eliminated the non-avian dinosaurs.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) It was a time of high sea levels, a warm greenhouse climate that cooled over its course, the rise of flowering plants, and some of the best-known dinosaur faunas, including *Tyrannosaurus rex* and *Triceratops*.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html)
| Key fact | Detail |
|---|---|
| Time span | 100.5 to 66 million years ago; the second epoch of the Cretaceous Period[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) |
| Stages | Cenomanian (93.9 Ma), Turonian (89.8 Ma), Coniacian (86.3 Ma), Santonian (83.6 Ma), Campanian (72.1 Ma), Maastrichtian (66.0 Ma)[2](https://cretaceous.stratigraphy.org/gssps) |
| Climate | Warmer than present with little or no polar ice, but a global cooling trend through the epoch that correlates with declining atmospheric carbon dioxide[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) • [3](https://www.cambridge.org/core/journals/geological-magazine/article/abs/review-of-terrestrial-and-marine-climates-in-the-cretaceous-with-implications-for-modelling-the-greenhouse-earth/1485EF0FCA75E6CEE90ED6BA0313926F) |
| Sea level | At times 170 meters higher than today, flooding continents with shallow inland seas[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) |
| Western Interior Seaway | Split North America into two landmasses; at its largest more than 3,000 km long, almost 1,000 km wide and 760 m deep[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) |
| Plants | By the end of the Cretaceous, angiosperms made up more than 70% of terrestrial plant species globally[4](https://www.annualreviews.org/doi/pdf/10.1146/annurev.earth.26.1.379) |
| End | Chicxulub asteroid impact 66 million years ago, the second largest mass extinction after the end-Permian event[5](https://home.nps.gov/articles/000/cretaceous-period.htm) • [6](https://www.nps.gov/subjects/fossils/extinction-events.htm) |
## Stratigraphy and stages
The Late Cretaceous is divided into six stages, each defined by a boundary marker (GSSP) ratified by the [International Commission on Stratigraphy](https://www.edgepedia.org/international-commission-on-stratigraphy). In order from oldest to youngest, with the numerical age of each stage's base, they are the [Cenomanian](https://www.edgepedia.org/cenomanian) (93.9 Ma), Turonian (89.8 Ma), Coniacian (86.3 Ma), Santonian (83.6 Ma), Campanian (72.1 ± 0.2 Ma), and [Maastrichtian](https://www.edgepedia.org/maastrichtian) (66.0 Ma).[2](https://cretaceous.stratigraphy.org/gssps) The epoch's close at 66 Ma is also the Mesozoic Era's close, followed by the Paleogene, the first period of the Cenozoic.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html)
## Climate
The [Cretaceous](https://www.edgepedia.org/cretaceous) as a whole was one of the warmest periods of the last 140 million years, with temperate rainforests growing close to ice-free poles.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) Both marine and non-marine records show a global cooling trend throughout Late Cretaceous time that appears to correlate with declining atmospheric carbon dioxide.[3](https://www.cambridge.org/core/journals/geological-magazine/article/abs/review-of-terrestrial-and-marine-climates-in-the-cretaceous-with-implications-for-modelling-the-greenhouse-earth/1485EF0FCA75E6CEE90ED6BA0313926F) Sea surface temperatures of 33 °C and above were typical of the mid-Cretaceous greenhouse, and cooling continued at low, middle, and high paleolatitude sites into the late epoch.[7](https://doi.org/10.1038/ncomms5194)
**Latitudinal gradients.** In the mid-Campanian to end-Maastrichtian, the difference between low-latitude and higher-latitude sea surface temperatures strengthened to roughly 19–21 °C, implying global surface-ocean cooling or changes in ocean heat transport.[8](https://www.sciencedirect.com/science/article/pii/S0012825217303859) Despite this marked cooling, no major ice sheet formed during the Late Cretaceous, a contrast with superficially similar cooling intervals later in the Cenozoic.[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC4082635/)
## Geography and the Western Interior Seaway
By the end of the Cretaceous, the breakup of Pangaea had moved the continents almost into their present positions.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) High sea levels split several landmasses. In North America, the [Western Interior Seaway](https://www.edgepedia.org/western-interior-seaway) divided the continent into two, and at its largest extent the sea was more than 3,000 kilometers long, almost 1,000 kilometers wide, and 760 meters deep.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) The seaway stretched between the [Gulf of Mexico](https://www.edgepedia.org/gulf-of-mexico) and the [Arctic Ocean](https://www.edgepedia.org/arctic-ocean), and during maximum transgression reached a width of at least 1,000 miles (1,600 km) across Utah into Iowa.[5](https://home.nps.gov/articles/000/cretaceous-period.htm) It advanced, retreated, and re-advanced many times before the most extensive interior seaway recorded in North America drowned much of the western continent.[5](https://home.nps.gov/articles/000/cretaceous-period.htm)
Near the end of the period, the Laramide Orogeny began lifting western North America from the sea in a series of uplifts, volcanic episodes, and erosion events that continued into the Cenozoic.[5](https://home.nps.gov/articles/000/cretaceous-period.htm)
## Life
**Flowering plants.** Angiosperms, which appear in the fossil record more than 100 million years ago during the Cretaceous, rapidly diversified and became the dominant land plants, a position they still hold.[5](https://home.nps.gov/articles/000/cretaceous-period.htm) By the end of the Cretaceous, at least half of the living angiosperm orders were present and angiosperms accounted for more than 70% of terrestrial plant species globally.[4](https://www.annualreviews.org/doi/pdf/10.1146/annurev.earth.26.1.379) Their spread is linked to expanding insect pollination, which had begun with gymnosperms in the Jurassic but grew much larger with the flowering plants.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html)
**Dinosaurs.** The Late Cretaceous was the height of dinosaur diversity.[10](https://www.nps.gov/subjects/fossils/scenes-of-parks-and-evolution.htm) In North America, the last 10 million years of the period produced some of the best-known faunas in the world: tyrannosaurs such as *Tyrannosaurus*, diverse small theropods, ankylosaurs, pachycephalosaurs, horned ceratopsians such as *Triceratops*, and duck-billed hadrosaurs.[11](https://www.nps.gov/subjects/fossils/cretaceous-dinosaurs.htm) *T. rex* and *Triceratops* lived only at the very end of the period, around 68 to 66 million years ago.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) Hadrosaurs ground vast amounts of plant matter with hundreds of tiny teeth, and the new faunas may relate to the spread of flowering plants.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) • [11](https://www.nps.gov/subjects/fossils/cretaceous-dinosaurs.htm) Sauropods disappeared from North America around the time the seaway formed and returned only with the titanosaur *Alamosaurus* a few million years before the period's end.[11](https://www.nps.gov/subjects/fossils/cretaceous-dinosaurs.htm) In the southern hemisphere, the Cretaceous produced the largest land animals ever known, the titanosaurs.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) The seas held mosasaurs, plesiosaurs, and ammonites, and the skies held both birds and pterosaurs.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html)
**Mammals.** Mammals of the time were small, furry animals, a relatively minor component of ecosystems dominated by dinosaurs.[1](https://www.nhm.ac.uk/discover/the-cretaceous-period.html) Nevertheless, the lineages characteristic of Paleogene faunas began their diversification in the Late Cretaceous: fossil and rock records from western North America show accelerated increases in mammal and angiosperm species richness during the epoch.[12](https://www.sciencedirect.com/science/article/pii/S0012825223003197)
## The end-Cretaceous extinction
The epoch and the period ended with the second largest mass extinction in Earth's history, behind only the end-Permian event.[6](https://www.nps.gov/subjects/fossils/extinction-events.htm) It killed all dinosaurs except birds, many groups of early birds, the pterosaurs, the marine reptiles, the shelled squid-like ammonites, and many other groups.[11](https://www.nps.gov/subjects/fossils/cretaceous-dinosaurs.htm) In family-level terms, 16% of marine families and 18% of land vertebrate families became extinct.[5](https://home.nps.gov/articles/000/cretaceous-period.htm)
The main cause is accepted to be the impact of an asteroid roughly 6 to 12 miles (10 to 20 km) across, which struck near the [Yucatán Peninsula](https://www.edgepedia.org/yucatan-peninsula) 66 million years ago and excavated the [Chicxulub crater](https://www.edgepedia.org/chicxulub-crater), nearly 120 miles (190 km) wide.[5](https://home.nps.gov/articles/000/cretaceous-period.htm) • [6](https://www.nps.gov/subjects/fossils/extinction-events.htm) The impact scattered crustal material into the atmosphere; as it fell back, it heated the air to oven-like levels, and lingering dust cut off sunlight, striking at the base of food webs on land and in water.[6](https://www.nps.gov/subjects/fossils/extinction-events.htm) Rocks spanning the boundary worldwide contain a thin clay layer with an abnormal concentration of iridium, an element rare at Earth's surface but common in asteroids, first identified by a team led by the physicist Luis Alvarez and his geologist son Walter.[6](https://www.nps.gov/subjects/fossils/extinction-events.htm) • [5](https://home.nps.gov/articles/000/cretaceous-period.htm)
**Volcanism.** The Deccan Traps of western India erupted enormous lava volumes within the same narrow window. Geochronologic work published in *Science* found the eruptions occurred within 50,000 years of the asteroid impact, and the researchers concluded that both events contributed to the extinction.[13](https://time.com/4059335/asteroid-volcano-dinosaur-extinction/) A review of Deccan stratigraphy identifies three volcanic phases, with the main phase at the end of the Maastrichtian ending coincident with the K–Pg boundary.[14](https://collaborate.princeton.edu/en/publications/the-cretaceous-tertiary-mass-extinction-chicxulub-impact-and-decc/) Other contributing stresses at the end of the epoch included falling sea level and the draining of continental seas, which destroyed shallow marine habitats.[6](https://www.nps.gov/subjects/fossils/extinction-events.htm)
## References
1. [The Cretaceous Period: What was Earth like before dinosaurs went extinct? Natural History Museum, London](https://www.nhm.ac.uk/discover/the-cretaceous-period.html)
2. [GSSPs, Subcommission on Cretaceous Stratigraphy, International Commission on Stratigraphy](https://cretaceous.stratigraphy.org/gssps)
3. [A review of terrestrial and marine climates in the Cretaceous with implications for modelling the 'Greenhouse Earth', Geological Magazine](https://www.cambridge.org/core/journals/geological-magazine/article/abs/review-of-terrestrial-and-marine-climates-in-the-cretaceous-with-implications-for-modelling-the-greenhouse-earth/1485EF0FCA75E6CEE90ED6BA0313926F)
4. [Ecological aspects of the Cretaceous flowering plant radiation, Annual Review of Earth and Planetary Sciences](https://www.annualreviews.org/doi/pdf/10.1146/annurev.earth.26.1.379)
5. [Cretaceous Period—145.0 to 66.0 MYA, U.S. National Park Service](https://home.nps.gov/articles/000/cretaceous-period.htm)
6. [Extinction Events, Fossils and Paleontology, U.S. National Park Service](https://www.nps.gov/subjects/fossils/extinction-events.htm)
7. [Evidence for global cooling in the Late Cretaceous, Nature Communications](https://doi.org/10.1038/ncomms5194)
8. [Cretaceous sea-surface temperature evolution: Constraints from TEX86 and planktonic foraminiferal oxygen isotopes, Earth-Science Reviews](https://www.sciencedirect.com/science/article/pii/S0012825217303859)
9. [Evidence for global cooling in the Late Cretaceous, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC4082635/)
10. [Scenes of Parks and Evolution, Fossils and Paleontology, U.S. National Park Service](https://www.nps.gov/subjects/fossils/scenes-of-parks-and-evolution.htm)
11. [Cretaceous Dinosaurs, Fossils and Paleontology, U.S. National Park Service](https://www.nps.gov/subjects/fossils/cretaceous-dinosaurs.htm)
12. [On the role of tectonics in stimulating the Cretaceous diversification of mammals, Earth-Science Reviews](https://www.sciencedirect.com/science/article/pii/S0012825223003197)
13. [Study Proposes Asteroid and Volcanic Eruptions Both Caused Dinosaur Extinction, Time](https://time.com/4059335/asteroid-volcano-dinosaur-extinction/)
14. [The Cretaceous-tertiary mass extinction, Chicxulub impact, and Deccan volcanism (G. Keller, 2012), Princeton University research portal](https://collaborate.princeton.edu/en/publications/the-cretaceous-tertiary-mass-extinction-chicxulub-impact-and-decc/)
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*Topic: Encyclopedia › Physical world and mathematics › Earth sciences › Geology and mineralogy › Geologic time and periods*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license