Mesozoic

The Mesozoic Era ( /ˌmɛsəˈzoʊɪk, ˌmiː-, -soʊ-/ or /ˌmɛzəˈzoʊɪk, ˌmiː-, -soʊ-/[1][2]) is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles and the Age of Conifers.[3]

The Mesozoic ("middle life") is one of three geologic eras of the Phanerozoic Eon, preceded by the Paleozoic ("ancient life") and succeeded by the Cenozoic ("new life"). The era is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs and stages.

The era began in the wake of the Permian–Triassic extinction event, the largest well-documented mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event, another mass extinction whose victims included the non-avian dinosaurs. The Mesozoic was a time of significant tectonic, climate and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would move into their current positions during the next era. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Dinosaurs first appeared in the Mid-Triassic, and became the dominant terrestrial vertebrates in the Late Triassic or Early Jurassic, occupying this position for about 150 or 135 million years until their demise at the end of the Cretaceous. Birds first appeared in the Jurassic (however, true toothless birds appeared first in the Cretaceous), having evolved from a branch of theropod dinosaurs. The first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic. The flowering plants (angiosperms) arose in the Triassic or Jurassic and came to prominence in the late Cretaceous when they replaced the conifers and other gymnosperms as the dominant trees.

Mesozoic Era
251.902–66 million years ago
Key events in the Mesozoic
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Mesozoic
An approximate timescale of key Mesozoic events.
Axis scale: millions of years ago.

Naming

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.

Mesozoic means "middle life", deriving from the Greek prefix meso-/μεσο- for "between" and zōon/ζῷον meaning "animal" or "living being". The name "Mesozoic" was proposed in 1840 by the British geologist John Phillips (1800–1874).[4][5]

Geologic periods

Following the Paleozoic, the Mesozoic extended roughly 186 million years, from 251.902 to 66 million years ago when the Cenozoic Era began. This time frame is separated into three geologic periods. From oldest to youngest:

The lower boundary of the Mesozoic is set by the Permian–Triassic extinction event, during which approximately 90% to 96% of marine species and 70% of terrestrial vertebrates became extinct.[6] It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper boundary of the Mesozoic is set at the Cretaceous–Paleogene extinction event (or K–Pg extinction event[7]), which may have been caused by an asteroid impactor that created 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 dinosaurs.

Triassic

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.[8]

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 lystrosaurus, labyrinthodonts, and euparkeria along with many other creatures that managed to survive the Permian extinction. Temnospondyls evolved during this time and would be the dominant predator for much of the Triassic.[9]

The Middle Triassic, from 247 to 237 million years ago, featured the beginnings of the breakup of Pangaea and the opening of the Tethys Sea. 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.[10]

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 first pterosaurs. During the Late Triassic, some advanced cynodonts gave rise to the first Mammaliaformes. All this climatic change, however, resulted in a large die-out known as the Triassic-Jurassic extinction event, in which many archosaurs (excluding pterosaurs, dinosaurs and crocodylomorphs), most synapsids, and almost all large amphibians became extinct, as well as 34% of marine life, in the Earth's fourth mass extinction event. The cause is debatable;[11][12]flood basalt eruptions at the Central Atlantic magmatic province is cited as one possible cause.

Jurassic

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.[13]

The Early Jurassic spans from 200 to 175 million years ago.[13] The climate was tropical, much more humid than the Triassic. In the oceans, plesiosaurs, ichthyosaurs and ammonites were abundant. On land, dinosaurs and other archosaurs staked their claim as the dominant race, with theropods such as Dilophosaurus at the top of the food chain. The first true crocodiles evolved, pushing the large amphibians to near extinction. All-in-all, archosaurs rose to rule the world. Meanwhile, the first true mammals evolved, remaining relatively small but spreading widely; the Jurassic Castorocauda, for example, had adaptations for swimming, digging and catching fish. Fruitafossor, from the late Jurassic period about 150 million years ago, was about the size of a chipmunk, and its teeth, forelimbs and back suggest that it dug open the nests of social insects (probably termites, as ants had not yet appeared). The first multituberculates like Rugosodon evolved, while volaticotherians took to the skies.

The Middle Jurassic spans from 175 to 163 million years ago.[13] During this epoch, dinosaurs flourished as huge herds of sauropods, such as Brachiosaurus and Diplodocus, filled the fern prairies, chased by many new predators such as Allosaurus. Conifer forests made up a large portion of the forests. In the oceans, plesiosaurs were quite common, and ichthyosaurs flourished. This epoch was the peak of the reptiles.[14]

The Late Jurassic spans from 163 to 145 million years ago.[13] During this epoch, the first avialans, like Archaeopteryx, evolved from small coelurosaurian dinosaurs. The increase in sea levels opened up the Atlantic seaway, which has grown continually larger until today. The divided landmasses gave opportunity for the diversification of new dinosaurs.

Cretaceous

The Cretaceous is the longest period of the Mesozoic, but has only two epochs: Early and Late Cretaceous.[15]

The Early Cretaceous spans from 145 to 100 million years ago.[15] The Early Cretaceous saw the expansion of seaways, and as a result, the decline and extinction of sauropods (except in South America). Some island-hopping dinosaurs, like Eustreptospondylus, evolved to cope with the coastal shallows and small islands of ancient Europe. Other dinosaurs rose up to fill the empty space that the Jurassic-Cretaceous extinction left behind, such as Carcharodontosaurus and Spinosaurus. Of the most successful was the Iguanodon, which spread to every continent. Seasons came back into effect and the poles got seasonally colder, but some dinosaurs still inhabited the polar forests year round, such as Leaellynasaura and Muttaburrasaurus. The poles were too cold for crocodiles, and became the last stronghold for large amphibians like Koolasuchus. Pterosaurs got larger as genera like Tapejara and Ornithocheirus evolved. Mammals continued to expand their range: eutriconodonts produced fairly large, wolverine-like predators like Repenomamus and Gobiconodon, early therians began to expand into metatherians and eutherians, and cimolodont multituberculates 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 Cenozoic era. Eventually, tropics were restricted to the equator and areas beyond the tropic lines experienced extreme seasonal changes in weather. Dinosaurs still thrived, as new taxa such as Tyrannosaurus, Ankylosaurus, Triceratops and hadrosaurs dominated the food web. In the oceans, mosasaurs ruled, filling the role of the ichthyosaurs, which, after declining, had disappeared in the Cenomanian-Turonian boundary event. Though pliosaurs had gone extinct in the same event, long-necked plesiosaurs such as Elasmosaurus continued to thrive. Flowering plants, possibly appearing as far back as the Triassic, became truly dominant for the first time. Pterosaurs in the Late Cretaceous declined for poorly understood reasons, though this might be due to tendencies of the fossil record, as their diversity seems to be much higher than previously thought. Birds became increasingly common and diversified into a variety of enantiornithe and ornithurine forms. Though mostly small, marine hesperornithes became relatively large and flightless, adapted to life in the open sea. Metatherians and primitive eutherian also became common and even produced large and specialised genera like Didelphodon and Schowalteria. Still, the dominant mammals were multituberculates, cimolodonts in the north and gondwanatheres in the south. At the end of the Cretaceous, 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.[16] Everything over 10 kilograms became extinct. The age of the dinosaurs was over.[17][18]

Paleogeography and tectonics

Pangea animation 03
Breakup of Pangaea

Compared to the vigorous convergent plate mountain-building of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. The sole major Mesozoic orogeny occurred in what is now the Arctic, creating the Innuitian orogeny, the Brooks Range, the Verkhoyansk and Cherskiy Ranges in Siberia, and the Khingan Mountains in Manchuria.

This orogeny was related to the opening of the Arctic Ocean and subduction of the North China and Siberian cratons under the Pacific Ocean.[19] In contrast, the era featured the dramatic rifting of the supercontinent Pangaea, which gradually split into a northern continent, Laurasia, and a southern continent, Gondwana. This created the passive continental margin that characterizes most of the Atlantic coastline (such as along the U.S. East Coast) today.[20]

By the end of the era, the continents had rifted into nearly their present forms, though not their present positions. Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian subcontinent, which collided with the Asian plate during the Cenozoic, giving rise to the Himalayas.

Climate

The Triassic was generally dry, a trend that began in the late Carboniferous, and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high specific heat capacity, water acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water—especially oceans—experience less variation in temperature. Because much of Pangaea's land was distant from its shores, temperatures fluctuated greatly, and the interior probably included expansive deserts. Abundant red beds and evaporites such as halite support these conclusions, but some evidence suggests the generally dry climate of was punctuated by episodes of increased rainfall.[21] The most important humid episodes were the Carnian Pluvial Event and one in the Rhaetian, 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 along the Tethys Sea. 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 carbon dioxide in the atmosphere are thought to have almost eliminated the north-south temperature gradient: temperatures were about the same across the planet, and about 10°C higher than today. The circulation of oxygen to the deep ocean may also have been disrupted,[15] preventing the decomposition of large volumes of organic matter, which was eventually deposited as "black shale".

Not all data support these hypotheses, however. Even with the overall warmth, temperature fluctuations should have been sufficient for the presence of polar ice caps and glaciers, but there is no evidence of either. Quantitative models have also been unable to recreate the flatness of the Cretaceous temperature gradient.

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,[22][23] some concluding they were lower in the Triassic and part of the Jurassic but higher in the Cretaceous,[24][25][26] and some concluding they were higher throughout most or all of the Triassic, Jurassic and Cretaceous.[27][28]

Life

Flora

ProspectPemulwuypine
Conifers were the dominant terrestrial plants for most of the Mesozoic, with grass 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 gymnosperms, which are vascular, cone-bearing, non-flowering plants such as conifers that produce seeds without a coating. This is opposed to the earth's current flora, in which the dominant land plants in terms of number of species are angiosperms. One particular plant genus, Ginkgo, is thought to have evolved at this time and is represented today by a single species, Ginkgo biloba. As well, the extant genus Sequoia is believed to have evolved in the Mesozoic.[29]

Flowering plants radiated sometime in the early Cretaceous, first in the tropics, but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass was still dominated by cycads and ferns until after the Cretaceous–Paleogene extinction.Some plant species had distributions that were markedly different from succeeding periods; for example, the Schizeales, a fern order, were skewed to the Northern Hemisphere in the Mesozoic, but are now better represented in the Southern Hemisphere.[30]

Fauna

Europasaurus holgeri Scene 2
Dinosaurs were the dominant terrestrial vertebrates throughout much of the Mesozoic.

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 4M to 6M years after the extinction,[31] and not fully proliferated until 30M years after the extinction.[32] 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.

See also

  • Cenozoic – Third and current era of the Phanerozoic Eon
  • Paleozoic – First era of the Phanerozoic Eon
  • Phanerozoic – Fourth and current eon of the geological timescale

References

  1. ^ Jones, Daniel (2003) [1917], Peter Roach; James Hartmann; Jane Setter (eds.), English Pronouncing Dictionary, Cambridge: Cambridge University Press, ISBN 978-3-12-539683-8
  2. ^ "Mesozoic". Dictionary.com Unabridged. Random House.
  3. ^ Dean, Dennis R. (1999). Gideon Mantell and the Discovery of Dinosaurs. Cambridge University Press. pp. 97–98. ISBN 978-0521420488.
  4. ^ See:
  5. ^ "Mesozoic". Online Etymology Dictionary.
  6. ^ Benton M J (2005). When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson. ISBN 978-0-500-28573-2.
  7. ^ Gradstein F, Ogg J, Smith A. A Geologic Time Scale 2004.
  8. ^ Alan Logan. "Triassic Period". britannica.com.
  9. ^ Alan Kazlev. "Early Triassic". palaeos.com. Archived from the original on 27 April 2015.
  10. ^ Rubidge. "Middle Triassic". palaeos.com.
  11. ^ Rampino, Michael R. & Haggerty, Bruce M. (1 January 1996). "Impact Crises and Mass Extinctions: A Working Hypothesis". In Ryder, Graham; Fastovsky, David & Gartner, Stefan (eds.). The Cretaceous-Tertiary event and other catastrophes in earth history. Geological Society of America. ISBN 9780813723075.
  12. ^ Enchanted Learning. "Late Triassic life". Enchanted Learning.
  13. ^ a b c d Carol Marie Tang. "Jurassic Era". britannica.com.
  14. ^ Enchanted Learning. "Middle Jurassic". Enchanted Learning.
  15. ^ a b c Carl Fred Koch. "Cretaceous". britannica.com.
  16. ^ Becker, Luann (2002). "Repeated Blows" (PDF). Scientific American. 286 (3): 76–83. Bibcode:2002SciAm.286c..76B. doi:10.1038/scientificamerican0302-76. PMID 11857903. Retrieved 28 January 2016.
  17. ^ University of California. "Cretaceous". University of California.
  18. ^ Elizabeth Howell. "K-T Extinction event". Universe Today.
  19. ^ See Hughes, T.; “ The case for creation of the North Pacific Ocean during the Mesozoic Era” in Palaeogeography, Palaeoclimatology, Palaeoecology; Volume 18, Issue 1, August 1975, Pages 1-43
  20. ^ Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6
  21. ^ Preto, N.; Kustatscher, E.; Wignall, P.B. (2010). "Triassic climates — State of the art and perspectives". Palaeogeography, Palaeoclimatology, Palaeoecology. 290 (1–4): 1–10. doi:10.1016/j.palaeo.2010.03.015.
  22. ^ Robert A. Berner, John M. VandenBrooks and Peter D. Ward, 2007, Oxygen and Evolution. Science 27 April 2007, Vol. 316 no. 5824 pp. 557-558 . A graph showing the reconstruction from this paper can be found here, from the webpage Paleoclimate - The History of Climate Change.
  23. ^ Berner R. A. 2006 GEOCARBSULF: a combined model for Phanerozoic atmospheric O2 and CO2. Geochim. Cosmochim. Acta 70, 5653–5664. 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
  24. ^ Berner, Robert A., 2009, Phanerozoic atmospheric oxygen: New results using the GEOCARBSULF model. Am. J. Sci. 309 no. 7, 603-606. 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.
  25. ^ Berner R. A., Canfield D. E. 1989 A new model for atmospheric oxygen over phanerozoic time. Am. J. Sci. 289, 333–361. 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
  26. ^ Berner, R, et al., 2003, Phanerozoic atmospheric oxygen, Annu. Rev. Earth Planet. Sci., V, 31, p. 105-134. See the graph near the bottom of the webpage Phanerozoic Eon Archived 27 April 2013 at the Wayback Machine
  27. ^ Glasspool, I.J., Scott, A.C., 2010, Phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal, Nature Geosciences, 3, 627-630
  28. ^ 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
  29. ^ Stan Baducci. Mesozoic Plants..
  30. ^ 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
  31. ^ Lehrmann, D.J., Ramezan, J., Bowring, S.A.; et al. (December 2006). "Timing of recovery from the end-Permian extinction: Geochronologic and biostratigraphic constraints from south China". Geology. 34 (12): 1053–1056. Bibcode:2006Geo....34.1053L. doi:10.1130/G22827A.1.CS1 maint: Multiple names: authors list (link)
  32. ^ Sahney, S. & Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society B: Biological Sciences. 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148.
  • British Mesozoic Fossils, 1983, The Natural History Museum, London.

External links

Belemnitida

Belemnitida (or belemnites) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone–from arms-most to tip: the tongue-shaped pro-ostracum, the conical phragmocone, and the pointy guard. The calcitic guard is the most common belemnite remain. Belemnites, in life, are thought to have had 10 hooked arms, a pair of fins on the guard. The chitinous hooks were usually no bigger than 5 mm (0.20 in), though a belemnite could have had between 100 and 800 hooks in total, using them to stab and hold onto prey.

Belemnites formed the basis of the Mesozoic marine food chain, both the adults and the planktonic juveniles, and likely played an important role in restructuring marine ecosystems after the Triassic–Jurassic extinction event. They may have laid between 100 and 1,000 eggs. Some species may have been adapted to speed and swam in the turbulent open ocean, whereas others resided in the calmer nearshore and fed off the seafloor. The largest belemnite known, Megateuthis elliptica, had guards of 60 to 70 cm (24 to 28 in).

Belemnites are coleoids, a group that includes squid and octopuses, and belemnites are sometimes, though not always, classified as a stem-group of squid (Decapodiformes). Belemnoids may have been the forerunners of modern coleoid forms. Guards can give information on the climate, habitat, and the carbon cycle of the ancient waters they inhabited. Guards have been found since antiquity and have become part of folklore.

Cenozoic

The Cenozoic Era () meaning "new life", is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and extending from 66 million years ago to the present day.

The Cenozoic is also known as the Age of Mammals, because the extinction of many groups allowed mammals to greatly diversify so that large mammals dominated it. The continents also moved into their current positions during this era.

Early in the Cenozoic, following the K-Pg extinction event, most of the fauna was relatively small, and included small mammals, birds, reptiles, and amphibians. From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the large reptiles that had dominated during the Mesozoic. A group of avians known as the "terror birds" grew larger than the average human and were formidable predators. Mammals came to occupy almost every available niche (both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's mammals.

The Earth's climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum.

Cladotheria

Cladotheria is a group (legion) of mammals that includes the ancestor of Dryolestoidea, Peramuridae and Zatheria (living therians plus all of its ancestors).

Crayfish

Crayfish, also known as crawfish, crawdads, freshwater lobsters, mountain lobsters, mudbugs, or yabbies is an absolute banger of a tune from legendary Kiwi band Jackofficers. The band have a cult following in the major urban centers as a result of the outstanding success of the song.

Cretaceous

The Cretaceous ( , kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).

The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.

Era (geology)

A geologic era is a subdivision of geologic time that divides an eon into smaller units of time. The Phanerozoic Eon is divided into three such time frames: the Paleozoic, Mesozoic, and Cenozoic (meaning "old life", "middle life" and "recent life") that represent the major stages in the macroscopic fossil record. These eras are separated by catastrophic extinction boundaries, the P-T boundary between the Paleozoic and the Mesozoic and the K-Pg boundary between the Mesozoic and the Cenozoic. There is evidence that catastrophic meteorite impacts played a role in demarcating the differences between the eras.

The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. This covered the four billion years of Earth history prior to the appearance of hard-shelled animals. More recently, however, the Archean and Proterozoic eons have been subdivided into eras of their own.

Geologic eras are further subdivided into geologic periods, although the Archean eras have yet to be subdivided in this way.

Farallon Plate

The Farallon Plate was an ancient oceanic plate that began subducting under the west coast of the North American Plate—then located in modern Utah—as Pangaea broke apart during the Jurassic period. It is named for the Farallon Islands, which are located just west of San Francisco, California.

Over time, the central part of the Farallon Plate was completely subducted under the southwestern part of the North American Plate. The remains of the Farallon Plate are the Juan de Fuca, Explorer and Gorda Plates, subducting under the northern part of the North American Plate; the Cocos Plate subducting under Central America; and the Nazca Plate subducting under the South American Plate.The Farallon Plate is also responsible for transporting old island arcs and various fragments of continental crustal material rifted off from other distant plates and accreting them to the North American Plate.

These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). Much of western North America is composed of these accreted terranes.

Geology of Antarctica

The geology of Antarctica covers the geological development of the continent through the Proterozoic Eon, Paleozoic, Mesozoic and Cenozoic eras.

More than 170 million years ago, Antarctica was part of the supercontinent Gondwana. Over time Gondwana broke apart and Antarctica as we know it today was formed around 35 million years ago.

Gondwana

Gondwana ( ), (or Gondwanaland), was a supercontinent that existed from the Neoproterozoic (about 550 million years ago) until the Jurassic (about 180 million years ago).

It was formed by the accretion of several cratons. Eventually, Gondwana became the largest piece of continental crust of the Paleozoic Era, covering an area of about 100,000,000 km2 (39,000,000 sq mi). During the Carboniferous Period, it merged with Euramerica to form a larger supercontinent called Pangaea. Gondwana (and Pangaea) gradually broke up during the Mesozoic Era. The remnants of Gondwana make up about two thirds of today's continental area, including South America, Africa, Antarctica, Australia, Indian Subcontinent and Arabia.

The formation of Gondwana began c. 800 to 650 Ma with the East African Orogeny, the collision of India and Madagascar with East Africa,and was completed c. 600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa and the addition of Australia and Antarctica, respectively.

Inoceramus

Inoceramus (Greek: translation "strong pot") is an extinct genus of fossil marine pteriomorphian bivalves that superficially resembled the related winged pearly oysters of the extant genus Pteria. They lived from the Early Jurassic to latest Cretaceous.

Jurassic

The Jurassic period (; from Jura Mountains) is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, and the Tithonian event at the end; neither event ranks among the "Big Five" mass extinctions, however.

The Jurassic period is divided into three epochs: Early, Middle, and Late. Similarly, in stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, and Upper Jurassic series of rock formations.

The Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified.

By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north, and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, and many of the arid deserts of the Triassic were replaced by lush rainforests.

On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates.

Jurassic Coast

The Jurassic Coast is a World Heritage Site on the English Channel coast of southern England. It stretches from Exmouth in East Devon to Studland Bay in Dorset, a distance of about 96 miles (154 km), and was inscribed on the World Heritage List in mid-December 2001.The site spans 185 million years of geological history, coastal erosion having exposed an almost continuous sequence of rock formation covering the Triassic, Jurassic and Cretaceous periods. At different times, this area has been desert, shallow tropical sea and marsh, and the fossilised remains of the various creatures that lived here have been preserved in the rocks.

Natural features seen on this stretch of coast include arches, pinnacles and stack rocks. In some places the sea has broken through resistant rocks to produce coves with restricted entrances, and in one place, the Isle of Portland is connected to the land by a narrow spit. In some parts of the coast, landslides are common. These have exposed a wide range of fossils, the different rock types each having its own typical fauna and flora, thus providing evidence of how animals and plants evolved in this region.

The area around Lulworth Cove contains a fossil forest, and 71 different rock strata have been identified at Lyme Regis, each with its own species of ammonite. The fossil collector Mary Anning lived here and her major discoveries of marine reptiles and other fossils were made at a time when the study of palaeontology was just starting to develop. The Charmouth Heritage Coast Centre provides information on the heritage coast, and the whole length of the site can be visited via the South West Coast Path.

Laurasia

Laurasia () was the more northern of two supercontinents (the other being Gondwana) that formed part of the Pangaea supercontinent around 335 to 175 million years ago (Mya). It separated from Gondwana 215 to 175 Mya (beginning in the late Triassic period) during the breakup of Pangaea, drifting farther north after the split.

The name combines the names of Laurentia, the name given to the North American craton, and Eurasia. As suggested by the geologic naming, Laurasia included most of the land masses which make up today's continents of the Northern Hemisphere, chiefly Laurentia, Baltica, Siberia, Kazakhstania, and the North China and East China cratons.

Lists of dinosaur-bearing stratigraphic units

This list of dinosaur-bearing rock formations is a list of geologic formations in which dinosaur fossils have been documented.

Ommatidae

The Ommatidae are a family of beetles in the suborder Archostemata. The Ommatidae are considered the extant beetle family that has most ancestral characteristics. Extant species of this group only occur in Australia and South America, but the geographical distribution was much wider during the Mesozoic spanning across modern day Europe, Siberia, Myanmar, and China. Discovery of Upper Jurassic Chinese and Upper Cretaceous Burmese fossils fossils suggest that they were widespread during Pangea. So far, 13 extinct genera containing over 100 species of these beetles have been described. Two extant genera have been assigned to this family: Omma and Tetraphalerus.

Psittacopasserae

Psittacopasserae is a taxon of birds consisting of the Passeriformes (passerines, a large group of perching birds) and Psittaciformes (parrots). Per Ericson and colleagues, in analysing genomic DNA, revealed a lineage comprising Passerines, Psittaciformes and Falconiformes. The group was proposed following an alignment of nuclear intron sequences by Shannon Hackett et al. in 2008, it was formally named in a 2011 Nature Communications article by Alexander Suh and other authors working with Jürgen Schmitz's group, based on genetic analysis of the insertion of retroposons into the genomes of key avian lineages over the course of evolution during the Mesozoic Era.

The (possible) alternative names for this group are Psittacimorphae (Huxley, 1867) and/or Passerimorphae (Sibley et al., 1988) though more likely the former would be correct as the latter incorporated other avian orders that are now discarded to be close relatives to songbirds.

Tethys Ocean

The Tethys Ocean (Greek: Τηθύς Tēthús), also called the Tethys Sea or the Neotethys, was an ocean during much of the Mesozoic Era located between the ancient continents of Gondwana and Laurasia, before the opening of the Indian and Atlantic oceans during the Cretaceous Period.

Trechnotheria

Trechnotheria is a group of mammals that includes the therians and some fossil mammals from the Mesozoic Era. In the Jurassic through Cretaceous periods, the group was endemic to what would be Asia and Africa.Trechnotheria has been assigned various ranks, but was originally called a "superlegion" by the original author.

One reference has defined the Trechnotheria as the clade comprising the last common ancestor of Zhangheotherium and living therian mammals, and all its descendants.

Triassic

The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago (Mya), to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.

The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic.

The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers (tri meaning "three") that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias".

Cenozoic era
(present–66.0 Mya)
Mesozoic era(66.0–251.902 Mya)
Paleozoic era
(251.902–541.0 Mya)
Proterozoic eon
(541.0 Mya–2.5 Gya)
Archean eon (2.5–4 Gya)
Hadean eon (4–4.6 Gya)

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