Mesozoic Era ( /ˌmɛsəˈzoʊɪk, ˌmiː-, -soʊ-/ or
/ˌmɛzəˈzoʊɪk, ˌmiː-, -soʊ-/) is an interval of
geological time from about 252 to 66 million years ago. It
is also called the Age of Reptiles, a phrase introduced by the 19th
Gideon Mantell who viewed it as dominated by
diapsids such as Iguanodon, Megalosaurus,
Pterodactylus. This Era is also called from a paleobotanist view the
Age of Conifers.
Mesozoic means "middle life", deriving from the Greek prefix
meso-/μεσο- for "between" and zōon/ζῷον meaning "animal" or
"living being". It 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 which is known for having killed off non-avian dinosaurs,
as well as other plant and animal species. The
Mesozoic was a time of
significant tectonic, climate and evolutionary activity. The era
witnessed the gradual rifting of the supercontinent
separate landmasses that would eventually move into their current
positions. The climate of the
Mesozoic was varied, alternating between
warming and cooling periods. Overall, however, the Earth was hotter
than it is today. Dinosaurs appeared in the Late
Triassic and became
the dominant terrestrial vertebrates early in the Jurassic, occupying
this position for about 135 million years until their demise at the
end of the Cretaceous. Birds first appeared in the Jurassic, 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.
1 Geologic periods
2 Paleogeography and tectonics
5 See also
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:
Triassic (251.902 to 201.3 million years ago)
Jurassic (201.3 to 145 million years ago)
Cretaceous (145 to 66 million years ago)
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. 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
Cretaceous–Paleogene extinction event (or
K–Pg extinction event), which may have been caused by the
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
Triassic ranges roughly from 252 million to 201 million years ago.
Triassic is a time in Earth's history bracketed between the
Extinction and the Triassic–
Jurassic extinction event, two
of the big five, and precedes the
Jurassic Period. It has three major
epochs: the Early Triassic, the Middle
Triassic and the Late
Triassic was between about 252 million to 247 million years
ago and was dominated by deserts as
Pangaea had not yet broken up,
thus the interior was nothing but arid. The Earth had just witnessed a
massive die-off in which 95% of all life became extinct. The most
common vertebrate life on earth were Lystrosaurus, labyrinthodonts,
Euparkeria along with many other creatures that managed to survive
the Great Dying. Temnospondyls evolved during this time and would be
the dominant predator for much of the Triassic.
Plateosaurus (a prosauropod)
Triassic spans roughly from 247 million to 237 million
years ago. The Middle
Triassic featured the beginnings of the breakup
of Pangaea, and the opening of the Tethys Sea. The ecosystem had
recovered from the devastation that was the Great Dying. Algae,
sponge, corals, and crustaceans all had recovered, and the reptiles
began to get bigger and bigger. New aquatic reptiles evolved, such as
ichthyosaurs and nothosaurs. Meanwhile, on land, pine forests
flourished, as did groups of insects like mosquitoes and fruit flies.
The first ancient crocodilians evolved, which sparked competition with
the large amphibians that had since ruled the freshwater world.
Triassic spans roughly from 237 million to 201 million years
ago. Following the bloom of the Middle Triassic, the Late Triassic
featured frequent heat spells, as well as moderate precipitation
(10-20 inches per year). The recent warming led to a boom of reptilian
evolution on land as the first true dinosaurs evolved, as well as
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-
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 fourth mass
extinction event of the world. The cause is debatable.
Jurassic ranges from 200 million years to 145 million years ago
and features 3 major epochs: The Early Jurassic, the Middle Jurassic,
and the Late Jurassic.
Jurassic spans from 200 million years to 175 million years
ago. The climate was much more humid than the Triassic, and as a
result, the world was very tropical. In the oceans, plesiosaurs,
ichthyosaurs and ammonites were abundant. On land, dinosaurs and other
archosaurs stake their claim as the dominant race of the land, with
species such as
Dilophosaurus at the top. The first true crocodiles
evolved, pushing out the large amphibians to near extinction.
All-in-all, archosaurs rise to rule the world. Meanwhile, the first
true mammals evolve, remaining relatively small sized but otherwise
expanding ecologically; 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 broke open the nest of social insects to prey on them (probably
termites, as ants had not yet appeared). The first multituberculates
Rugosodon evolve, while volaticotherians take to the skies.
Jurassic spans from 175 million to 163 million years
ago. During this epoch, dinosaurs flourished as huge herds of
sauropods, such as
Brachiosaurus and Diplodocus, filled the fern
prairies of the Middle Jurassic. Many other predators rose as well,
such as Allosaurus.
Conifer forests made up a large portion of the
forests. In the oceans, plesiosaurs were quite common, and
ichthyosaurs were flourishing. This epoch was the peak of the
Jurassic spans from 163 million to 145 million years ago.
During the Late Jurassic, the first avialans, like Archaeopteryx,
evolved from small coelurosaurian dinosaurs. The increase in
sea-levels opened up the
Atlantic sea way which would continue to get
larger over time. The divided world would give opportunity for the
diversification of new dinosaurs.
Cretaceous is the longest period in the Mesozoic, but has only two
epochs: the Early Cretaceous, and the Late Cretaceous.
Tylosaurus (a mosasaur) hunting Xiphactinus
Cretaceous spans from 145 million to 100 million years
ago. 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
Cretaceous extinction left behind, such as
Carcharodontosaurus and Spinosaurus. Of the most successful would be
Iguanodon which spread to every continent. Seasons came back into
effect and the poles got seasonally colder, but dinosaurs still
inhabited this area like the
inhabited the polar forests year-round. Since it was too cold for
crocodiles, it was the last stronghold for large amphibians, like
Koolasuchus. Pterosaurs got larger as species like Tapejara and
Ornithocheirus evolved. Mammals continued to expand ecologically;
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 large components of the fossil record.
Cretaceous spans from 100 million to 66 million years ago.
Cretaceous featured a cooling trend that would continue on in
Cenozoic period. Eventually, tropics were restricted to the
equator and areas beyond the tropic lines featured extreme seasonal
changes in weather. Dinosaurs still thrived as new species such as
Triceratops and hadrosaurs dominated the
food web. In the oceans, mosasaurs ruled the seas, 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 fossil record bias as their diversity seems to be
much higher than previously thought. Birds became increasingly common
and diverse, diversifying in a variety of enantiornithe and
ornithurine forms. Though mostly small, marine
relatively large and flightless, adapted to life in the open sea.
Metatherians and primitive eutherian also became common and even
produced large and specialised species like
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 was continuing, 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-T Extinction, the fifth
and most recent mass extinction event, in which 75% of life on earth
became extinct, including all non-avian dinosaurs. Everything over
10 kilograms became extinct. The age of the dinosaurs was
Paleogeography and tectonics
Breakup of Pangaea
Compared to the vigorous convergent plate mountain-building of the
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
subduction of the North China and Siberian cratons under the Pacific
Ocean. Nevertheless, the era featured the dramatic rifting of the
Pangaea 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.
By the end of the era, the continents had rifted into nearly their
North America and Eurasia, while
Gondwana split into South America, Africa, Australia,
the Indian subcontinent, which collided with the Asian plate during
the Cenozoic, the impact giving rise to the Himalayas.
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 the oceans—experience less variation in
temperature. Because much of the land that constituted
distant from the oceans, temperatures fluctuated greatly, and the
Pangaea probably included expansive areas of desert.
Abundant red beds and evaporites such as halite support these
conclusions, but evidence exists that the generally dry climate of the
Triassic was punctuated by episodes of increased rainfall. The
most important humid episodes were the
Carnian Pluvial Event and one
in the Rhaetian, a few million years before the Triassic–Jurassic
Sea levels began to rise during the Jurassic, which was 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) more than today, which flooded coastal areas.
Pangaea began to rift into smaller divisions, bringing
more land area in contact with the ocean by forming the Tethys Sea.
Temperatures continued to increase and 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. Higher levels of carbon dioxide in the atmosphere are
thought to have caused the world temperature gradient from north to
south to become almost flat: temperatures were about the same across
the planet. Average temperatures were also higher than today by about
10°C. The circulation of oxygen to the deep ocean may also have been
disrupted.[dubious – discuss] For this reason, large volumes of
organic matter that was unable to decompose accumulated, eventually
being deposited as "black shale".
Not all of the 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.[citation
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, some concluding they were
lower in the
Triassic and part of the
Jurassic but higher in the
Cretaceous, and some concluding they were higher
throughout most or all of the Triassic,
Conifers were the dominant terrestrial plants for most of the
Mesozoic. 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
Ginkgo biloba. As well, the extant genus Sequoia is
believed to have evolved in the Mesozoic.
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.
Dinosaurs were the dominant terrestrial vertebrates throughout much of
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 the specialized animals that formed
complex ecosystems, with high biodiversity, complex food webs and a
variety of niches, took much longer to reestablish, recovery did not
begin until the start of the mid-Triassic, 4M to 6M years after the
extinction and was not complete until 30M years after the
Triassic extinction event.
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
Cretaceous provided for
further adaptive radiation. The
Jurassic was the height of archosaur
diversity, and the first birds and eutherian mammals also appeared.
Angiosperms 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 cycad and ferns
until after the Cretaceous–
Some have argued that insects diversified 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.
Wikisource has original works on the topic: Mesozoic
Wikimedia Commons has media related to Mesozoic.
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557-558 . A graph showing the reconstruction from this paper can be
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John M. VandenBrooks
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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.
^ 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
^ Berner, R, et al., 2003,
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Phanerozoic concentrations of
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biogeochemical cycling over Phanaerozoic time. Am. J. Sci. 304,
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Mesozoic Fossils, 1983, The Natural History Museum, London.
Geologic history of Earth
Quaternary (present–2.588 Mya)
Holocene (present–11.784 kya)
Pleistocene (11.784 kya–2.588 Mya)
Neogene (2.588–23.03 Mya)
Pliocene (2.588–5.333 Mya)
Miocene (5.333–23.03 Mya)
Paleogene (23.03–66.0 Mya)
Oligocene (23.03–33.9 Mya)
Eocene (33.9–56.0 Mya)
Paleocene (56.0–66.0 Mya)
Cretaceous (66.0–145.0 Mya)
Late (66.0–100.5 Mya)
Early (100.5–145.0 Mya)
Jurassic (145.0–201.3 Mya)
Late (145.0–163.5 Mya)
Middle (163.5–174.1 Mya)
Early (174.1–201.3 Mya)
Triassic (201.3–251.902 Mya)
Late (201.3–237 Mya)
Middle (237–247.2 Mya)
Early (247.2–251.902 Mya)
Permian (251.902–298.9 Mya)
Lopingian (251.902–259.8 Mya)
Guadalupian (259.8–272.3 Mya)
Cisuralian (272.3–298.9 Mya)
Carboniferous (298.9–358.9 Mya)
Pennsylvanian (298.9–323.2 Mya)
Mississippian (323.2–358.9 Mya)
Devonian (358.9–419.2 Mya)
Late (358.9–382.7 Mya)
Middle (382.7–393.3 Mya)
Early (393.3–419.2 Mya)
Silurian (419.2–443.8 Mya)
Pridoli (419.2–423.0 Mya)
Ludlow (423.0–427.4 Mya)
Wenlock (427.4–433.4 Mya)
Llandovery (433.4–443.8 Mya)
Ordovician (443.8–485.4 Mya)
Late (443.8–458.4 Mya)
Middle (458.4–470.0 Mya)
Early (470.0–485.4 Mya)
Cambrian (485.4–541.0 Mya)
Furongian (485.4–497 Mya)
Series 3 (497–509 Mya)
Series 2 (509–521 Mya)
Terreneuvian (521–541.0 Mya)
(541.0 Mya–2.5 Gya)
Neoproterozoic era (541.0 Mya–1 Gya)
Ediacaran (541.0-~635 Mya)
Cryogenian (~635-~720 Mya)
Tonian (~720 Mya-1 Gya)
Mesoproterozoic era (1–1.6 Gya)
Stenian (1-1.2 Gya)
Ectasian (1.2-1.4 Gya)
Calymmian (1.4-1.6 Gya)
Paleoproterozoic era (1.6–2.5 Gya)
Statherian (1.6-1.8 Gya)
Orosirian (1.8-2.05 Gya)
Rhyacian (2.05-2.3 Gya)
Siderian (2.3-2.5 Gya)
Archean eon² (2.5–4 Gya)
Neoarchean (2.5–2.8 Gya)
Mesoarchean (2.8–3.2 Gya)
Paleoarchean (3.2–3.6 Gya)
Eoarchean (3.6–4 Gya)
Hadean eon² (4–4.6 Gya)
kya = thousands years ago. Mya = millions years ago.
Gya = billions
years ago.¹ =
Phanerozoic eon. ² =
Source: (2017/02). International Commission on Stratigraphy. Retrieved
13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic
and Geochronologic Units USGS Retrieved 10 March 2013.