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Mesozoic Era
251.902 ± 0.024 – 66.0 Ma

The Mesozoic Era (

tectonic break-up of Pangaea. The Mesozoic is the middle of the three eras since complex life evolved: the Paleozoic, the Mesozoic, and the Cenozoic

The era began in the wake of the

flowering plants
appeared in the early Cretaceous Period and would rapidly diversify throughout the end of the era, replacing conifers and other gymnosperms as the dominant group of plants.


The phrase "Age of Reptiles" was introduced by the 19th century paleontologist Gideon Mantell who viewed it as dominated by diapsids such as Iguanodon, Megalosaurus, Plesiosaurus, and Pterodactylus.

The current name was proposed in 1840 by the British geologist John Phillips (1800–1874). "Mesozoic" literally means 'middle life', deriving from the Greek prefix meso- (μεσο- 'between') and zōon (ζῷον 'animal, living being').[3][4] In this way, the Mesozoic is comparable to the Cenozoic (lit.'new life') and Paleozoic ('old life') Eras as well as the Proterozoic ('earlier life') Eon.

The Mesozoic Era was originally described as the "secondary" era, following the "primary" (Paleozoic), and preceding the Tertiary.[5]

Geologic periods

Following the Paleozoic, the Mesozoic extended roughly 186 million years, from 251.902 to 66 million years ago when the

. From oldest to youngest:

The lower boundary of the Mesozoic is set by the

Chicxulub Crater on the Yucatán Peninsula. Towards the Late Cretaceous, large volcanic eruptions are also believed to have contributed to the Cretaceous–Paleogene extinction event. Approximately 50% of all genera became extinct, including all of the non-avian


The Triassic ranges roughly from 252 million to 201 million years ago, preceding the Jurassic Period. The period is bracketed between the Permian–Triassic extinction event and the Triassic–Jurassic extinction event, two of the "big five", and it is divided into three major epochs: Early, Middle, and Late Triassic.[9]

The Early Triassic, about 252 to 247 million years ago, was dominated by deserts in the interior of the Pangaea supercontinent. The Earth had just witnessed a massive die-off in which 95% of all life became extinct, and the most common vertebrate life on land were


The Middle Triassic, from 247 to 237 million years ago, featured the beginnings of the breakup of Pangaea and the opening of the Tethys Ocean. Ecosystems had recovered from the Permian extinction. Algae, sponge, corals, and crustaceans all had recovered, and new aquatic reptiles evolved, such as ichthyosaurs and nothosaurs. On land, pine forests flourished, as did groups of insects like mosquitoes and fruit flies. Reptiles began to get bigger and bigger, and the first crocodilians and dinosaurs evolved, which sparked competition with the large amphibians that had previously ruled the freshwater world, respectively mammal-like reptiles on land.[11]

Following the bloom of the Middle Triassic, the Late Triassic, from 237 to 201 million years ago, featured frequent heat spells and moderate precipitation (10–20 inches per year). The recent warming led to a boom of dinosaurian evolution on land as those one began to separate from each other (Nyasasaurus from 243 to 210 million years ago, approximately 235–30 ma, some of them separated into Sauropodomorphs, Theropods and Herrerasaurids), as well as the first

flood basalt eruptions at the Central Atlantic magmatic province
is cited as one possible cause.


The Jurassic ranges from 200 million years to 145 million years ago and features three major epochs: The Early Jurassic, the Middle Jurassic, and the Late Jurassic.[14]

The Early Jurassic spans from 200 to 175 million years ago.


The Middle Jurassic spans from 175 to 163 million years ago.

The Late Jurassic spans from 163 to 145 million years ago.

dinosaurs. The increase in sea levels opened up the Atlantic seaway, which has grown continually larger until today. The further separation of the continents gave opportunity for the diversification of new dinosaurs.


The Cretaceous is the longest period of the Mesozoic, but has only two epochs: Early and Late Cretaceous.

The Early Cretaceous spans from 145 to 100 million years ago.

went on to become common in the fossil record.

The Late Cretaceous spans from 100 to 66 million years ago. The Late Cretaceous featured a cooling trend that would continue in the

Deccan traps and other volcanic eruptions were poisoning the atmosphere. As this continued, it is thought that a large meteor smashed into earth 66 million years ago, creating the Chicxulub Crater in an event known as the K-Pg Extinction (formerly K-T), the fifth and most recent mass extinction event, in which 75% of life became extinct, including all non-avian dinosaurs.[18][19][20]

Paleogeography and tectonics

Compared to the vigorous convergent plate

Khingan Mountains
in Manchuria.

This orogeny was related to the opening of the

Atlantic coastline (such as along the U.S. East Coast) today.[22]

By the end of the era, the continents had rifted into nearly their present forms, though not their present positions.



The Triassic was generally dry, a trend that began in the late

, a few million years before the Triassic–Jurassic extinction event.

Sea levels began to rise during the Jurassic, probably caused by an increase in seafloor spreading. The formation of new crust beneath the surface displaced ocean waters by as much as 200 m (656 ft) above today's sea level, flooding coastal areas. Furthermore, Pangaea began to rift into smaller divisions, creating new shoreline around the Tethys Ocean. Temperatures continued to increase, then began to stabilize. Humidity also increased with the proximity of water, and deserts retreated.

The climate of the Cretaceous is less certain and more widely disputed. Probably, higher levels of

black shale".[24][25]

Different studies have come to different conclusions about the amount of oxygen in the atmosphere during different parts of the Mesozoic, with some concluding oxygen levels were lower than the current level (about 21%) throughout the Mesozoic,[26][27] some concluding they were lower in the Triassic and part of the Jurassic but higher in the Cretaceous,[28][29][30] and some concluding they were higher throughout most or all of the Triassic, Jurassic and Cretaceous.[31][32]



grasses becoming widespread in the Late Cretaceous. Flowering plants appeared late in the era but did not become widespread until the Cenozoic

The dominant land plant species of the time were

extant genus Sequoia is believed to have evolved in the Mesozoic.[33] Bennettitales, an extinct group of gymnosperms with foliage superficially resembling that of cycads gained a global distribution during the Late Triassic, and represented one of the most common groups of Mesozoic seed plants.[34]

Schizeales, a fern order, were skewed to the Northern Hemisphere in the Mesozoic, but are now better represented in the Southern Hemisphere.[35]


The extinction of nearly all animal species at the end of the Permian Period allowed for the radiation of many new lifeforms. In particular, the extinction of the large herbivorous pareiasaurs and carnivorous gorgonopsians left those ecological niches empty. Some were filled by the surviving cynodonts and dicynodonts, the latter of which subsequently became extinct.

Recent research indicates that it took much longer for the reestablishment of complex ecosystems with high biodiversity, complex food webs, and specialized animals in a variety of niches, beginning in the mid-Triassic 4 million to 6 million years after the extinction,[36] and not fully proliferated until 30 million years after the extinction.[37] Animal life was then dominated by various archosaurs: dinosaurs, pterosaurs, and aquatic reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs.

The climatic changes of the late Jurassic and Cretaceous favored further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first birds and eutherian mammals also appeared. Some have argued that insects diversified in symbiosis with angiosperms, because insect anatomy, especially the mouth parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms, and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose.[citation needed]

See also


  1. ^ "Mesozoic". Unabridged (Online). n.d.
  2. ^ See:
  3. ^ "Mesozoic". Online Etymology Dictionary.
  4. ^ Tang, Carol Marie. "Mesozoic Era". Encyclopædia Britannica. Encyclopædia Britannica. Retrieved 5 September 2019.
  5. ]
  6. .
  7. ^ Gradstein F, Ogg J, Smith A. A Geologic Time Scale 2004.
  8. ^ Alan Logan. "Triassic Period".
  9. S2CID 85411546
  10. ^ Rubidge. "Middle Triassic".
  11. .
  12. ^ Enchanted Learning. "Late Triassic life". Enchanted Learning.
  13. ^ a b c d Carol Marie Tang. "Jurassic Era".
  14. ^ Enchanted Learning. "Middle Jurassic". Enchanted Learning.
  15. ^ a b Carl Fred Koch. "Cretaceous".
  16. S2CID 26000791
  17. .
  18. ^ "Cretaceous". University of California.
  19. ^ Elizabeth Howell (3 February 2015). "K-T Extinction event". Universe Today.
  20. .
  21. .
  22. .
  23. .
  24. ^ Robert A. Berner, John M. VandenBrooks and Peter D. Ward, 2007, Oxygen and Evolution. Science 27 April 2007, Vol. 316 no. 5824 pp. 557–58 . A graph showing the reconstruction from this paper can be found here, from the webpage Paleoclimate – The History of Climate Change.
  25. ^ Berner R. A. 2006 GEOCARBSULF: a combined model for Phanerozoic atmospheric O2 and CO2. Geochim. Cosmochim. Acta 70, 5653–64. See the dotted line in Fig. 1 of Atmospheric oxygen level and the evolution of insect body size by Jon F. Harrison, Alexander Kaiser and John M. VandenBrooks
  26. ^ Berner, Robert A., 2009, Phanerozoic atmospheric oxygen: New results using the GEOCARBSULF model. Am. J. Sci. 309 no. 7, 603–06. A graph showing the reconstructed levels in this paper can be found on p. 31 of the book Living Dinosaurs by Gareth Dyke and Gary Kaiser.
  27. ^ Berner R. A., Canfield D. E. 1989 A new model for atmospheric oxygen over phanerozoic time. Am. J. Sci. 289, 333–61. See the solid line in Fig. 1 of Atmospheric oxygen level and the evolution of insect body size by Jon F. Harrison, Alexander Kaiser and John M. VandenBrooks
  28. ^ Berner, R, et al., 2003, Phanerozoic atmospheric oxygen, Annu. Rev. Earth Planet. Sci., V, 31, p. 105–34. See the graph near the bottom of the webpage Phanerozoic Eon Archived 27 April 2013 at the Wayback Machine
  29. ^ Glasspool, I.J., Scott, A.C., 2010, Phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal, Nature Geosciences, 3, 627–30
  30. ^ Bergman N. M., Lenton T. M., Watson A. J. 2004 COPSE: a new model of biogeochemical cycling over Phanaerozoic time. Am. J. Sci. 304, 397–437. See the dashed line in Fig. 1 of Atmospheric oxygen level and the evolution of insect body size by Jon F. Harrison, Alexander Kaiser and John M. VandenBrooks
  31. ^ Stan Baducci. Mesozoic Plants..
  32. ISSN 2296-6463
  33. ^ C.Michael Hogan. 2010. Fern. Encyclopedia of Earth. National council for Science and the Environment Archived 9 November 2011 at the Wayback Machine. Washington, DC
  34. .
  35. .
  • British Mesozoic Fossils, 1983, The Natural History Museum, London.

External links