Mesozoic
Encyclopedia
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time. The era began in the wake of the Permian-Triassic event, the largest mass extinction in Earth's history, and ended with the Cretaceous-Paleogene event, another mass extinction which is known for having killed off non-avian dinosaur
s, as well as other plant and animal species.
It is one of three geologic eras
of the Phanerozoic
eon. The division of time into eras dates back to Giovanni Arduino
, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" (making everything after, including the modern era, the "Tertiary"; the current term Quaternary
was later proposed for the modern era, following the same numbering principle). Lying between the Paleozoic
and the Cenozoic
, "Mesozoic" means "middle life", deriving from the Greek
prefix meso-/μεσο- for "between" and zōon/ζωον meaning "animal
" or "living being".
The Mesozoic was a time of tectonic
, climatic
and evolution
ary activity. The era witnessed the gradual rifting of the supercontinent
Pangaea
into separate landmasses which would eventually become the seven continents we are familiar with today. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was much hotter than it is today. Dinosaur
s would become the dominant terrestrial
vertebrate
group late in the Triassic
period, and would occupy this position for over 150 million years until their demise at the end of the Cretaceous
. Mammal
s also evolved during this era, but would remain small and modest until their ultimate rivals, the dinosaurs, disappeared.
The lower (Triassic) boundary 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 (Cretaceous) boundary is set at the Cretaceous-Tertiary (KT) extinction event (now more accurately called the Cretaceous–Paleogene (or K–Pg) extinction event), which may have been caused by the impactor that created Chicxulub Crater
on the Yucatán Peninsula
. Approximately 50% of all genera became extinct, including all of the non-avian
dinosaurs.
of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the supercontinent
Pangaea
. 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 present form. Laurasia
became North America
and Eurasia
, while Gondwana
split into South America
, Africa
, Australia
, Antarctica and the Indian subcontinent
, which collided with the Asia
n plate during the Cenozoic, the impact giving rise to the Himalayas.
At the beginning of the Mesozoic era, Africa was joined with Earth's other continents in Pangaea. Africa shared the supercontinent's relatively uniform fauna which was dominated by theropods, prosauropods and primitive ornithischians by the close of the Triassic period. Late Triassic fossils are found throughout Africa, but are more common in the south than north. The boundary separating the Triassic and Jurassic marks the advent of an extinction event with global impact, although African strata from this time period have not been thoroughly studied.
Early Jurassic strata are distributed in a similar fashion to Late Triassic beds, with more common outcrops in the south and less common fossil beds which are predominated by tracks to the north. As the Jurassic proceeded, larger and more iconic groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are neither well represented nor well studied in Africa. Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania. The Late Jurassic life of Tendaguru is very similar to that
found in western North America's Morrison Formation
.
Midway through the Mesozoic, about 150-160 million years ago, Madagascar separated from Africa, although it remained connected to India and the rest of the Gondwanan landmasses. Fossils from Madagascar include abelisaur
s and titanosaur
s. Later into the Early Cretaceous epoch, the India-Madagascar landmass separated from the rest of Gondwana. By the Late Cretaceous, Madagascar and India had permanently split ways and continued until later reaching their modern configurations.
By contrast to Madagascar, mainland Africa was relatively stable in position through-out the Mesozoic. Despite the stable position, major changes occurred to its relation to other landmasses as the remains of Pangaea continued to break apart. By the beginning of the Late Cretaceous epoch South America had split off from Africa, completing the southern half of the Atlantic Ocean. This event had a profound effect on global climate by altering ocean currents.
During the Cretaceous, Africa was populated by allosauroids and spinosaurids, including the largest known carnivorous dinosaurs. Titanosaur
s were significant herbivores in its ancient ecosystems. Cretaceous sites are more common than Jurassic ones, but are often unable to be dated radiometrically
making it difficult to know their exact ages. Paleontologist Louis Jacobs, who spent time doing field work in Malawi
, says that African beds are "in need of more field work" and will prove to be a "fertile ground...for discovery."
, 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 ocean
s—experience less variation in temperature. Because much of the land that constituted Pangaea was distant from the oceans, temperatures fluctuated greatly, and the interior of Pangaea probably included expansive areas of desert
. Abundant evidence of red beds
and evaporites such as salt
support these conclusions.
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. Furthermore, 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
. In fact, by the middle Cretaceous, equatorial ocean waters (perhaps as warm as 20°C in the deep ocean) may have been too warm for sea life, and land areas near the equator may have been deserts despite their proximity to water. The circulation of oxygen
to the deep ocean may also have been disrupted. 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 cap
s and glacier
s, but there is no evidence of either. Quantitative models have also been unable to recreate the flatness of the Cretaceous temperature gradient.
The amount of oxygen in the Mesozoic atmosphere varied widely, but was significantly higher on average (~26%) than in today's atmosphere (20 to 21%).
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
and carnivorous
dinocephalia
left those ecological niche
s empty. Some were filled by the surviving cynodont
s and dicynodont
s, the latter of which subsequently became extinct. 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.
The dominant land plant species of the time were gymnosperm
s, 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 species, the ginkgo biloba, is perceived to have evolved at this time and still exists today as the only surviving species from its phylum. As well, the extant genus sequoia
is believed to have evolved in the Mesozoic.
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 P-Tr extinction. Animal
life was then dominated by large archosaur
ian reptile
s: dinosaur
s, pterosaur
s, and aquatic reptiles such as ichthyosaur
s, plesiosaur
s, and mosasaur
s.
The climatic changes of the late Jurassic and Cretaceous provided for further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first bird
s and placental mammal
s 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 fern
s until after the KT extinction.
Some have argued that insect
s 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.
As the temperatures in the seas increased, the larger animals of the early Mesozoic gradually began to disappear while smaller animals of all kinds, including lizard
s, snake
s, and perhaps primate
s, evolved. The KT extinction exacerbated this trend. The large archosaurs became extinct, while birds and mammals thrived, as they do today.
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, as well as other plant and animal species.
It is one of three geologic eras
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
of the Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
eon. The division of time into eras dates back to Giovanni Arduino
Giovanni Arduino (geologist)
Giovanni Arduino was an Italian geologist who is known as the "Father of Italian Geology".Arduino was born at Caprino Veronese, Veneto. He was a mining specialist who developed possibly the first classification of geological time, based on study of the geology of northern Italy...
, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" (making everything after, including the modern era, the "Tertiary"; the current term Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
was later proposed for the modern era, following the same numbering principle). Lying between the Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
and the Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
, "Mesozoic" means "middle life", deriving from the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
prefix meso-/μεσο- for "between" and zōon/ζωον meaning "animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
" or "living being".
The Mesozoic was a time of tectonic
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, climatic
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
and evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary activity. The era witnessed the gradual rifting of the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
into separate landmasses which would eventually become the seven continents we are familiar with today. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was much hotter than it is today. Dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s would become the dominant terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
group late in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period, and would occupy this position for over 150 million years until their demise at the end of the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
. Mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s also evolved during this era, but would remain small and modest until their ultimate rivals, the dinosaurs, disappeared.
Geologic periods
Following the Paleozoic, the Mesozoic extended roughly 180 million years: from 251 million years ago (Mya) to when the Cenozoic era began 65 Mya. This time frame is separated into three geologic periods. From oldest to youngest:- TriassicTriassicThe Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
(251.0 Mya to 199.6 Mya) - JurassicJurassicThe Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
(199.6 Mya to 145.5 Mya) - CretaceousCretaceousThe Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
(145.5 Mya to 65.5 Mya)
The lower (Triassic) boundary is set by the Permian-Triassic extinction event
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
, during which approximately 90% to 96% of marine species and 70% of terrestrial vertebrates became extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
. It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper (Cretaceous) boundary is set at the Cretaceous-Tertiary (KT) extinction event (now more accurately called the Cretaceous–Paleogene (or K–Pg) extinction event), which may have been caused by the impactor that created Chicxulub Crater
Chicxulub Crater
The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named...
on the Yucatán Peninsula
Yucatán Peninsula
The Yucatán Peninsula, in southeastern Mexico, separates the Caribbean Sea from the Gulf of Mexico, with the northern coastline on the Yucatán Channel...
. Approximately 50% of all genera became extinct, including all of the non-avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
dinosaurs.
Paleogeography and tectonics
Compared to the vigorous convergent plate mountain-buildingOrogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
. Pangaea gradually split into a northern continent, Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
, and a southern continent, Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
. This created the passive continental margin that characterizes most of the Atlantic coastline (such as along the U.S. East Coast
East Coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...
) today.
By the end of the era, the continents had rifted into nearly their present form. Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
became North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
, while Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
split into South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Antarctica and the Indian subcontinent
South Asia
South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...
, which collided with the Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n plate during the Cenozoic, the impact giving rise to the Himalayas.
Africa
Early Jurassic strata are distributed in a similar fashion to Late Triassic beds, with more common outcrops in the south and less common fossil beds which are predominated by tracks to the north. As the Jurassic proceeded, larger and more iconic groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are neither well represented nor well studied in Africa. Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania. The Late Jurassic life of Tendaguru is very similar to that
Paleobiota of the Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has a wide assortment of taxa represented in its fossil record, including dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and...
found in western North America's Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
.
Midway through the Mesozoic, about 150-160 million years ago, Madagascar separated from Africa, although it remained connected to India and the rest of the Gondwanan landmasses. Fossils from Madagascar include abelisaur
Abelisaur
Abelisaurs were a group of ceratosaurian dinosaurs which lived in the Southern hemisphere during the Cretaceous period. Some well-known dinosaurs of this group include Abelisaurus, Carnotaurus, and Majungasaurus. They are known for their small arms...
s and titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
s. Later into the Early Cretaceous epoch, the India-Madagascar landmass separated from the rest of Gondwana. By the Late Cretaceous, Madagascar and India had permanently split ways and continued until later reaching their modern configurations.
By contrast to Madagascar, mainland Africa was relatively stable in position through-out the Mesozoic. Despite the stable position, major changes occurred to its relation to other landmasses as the remains of Pangaea continued to break apart. By the beginning of the Late Cretaceous epoch South America had split off from Africa, completing the southern half of the Atlantic Ocean. This event had a profound effect on global climate by altering ocean currents.
During the Cretaceous, Africa was populated by allosauroids and spinosaurids, including the largest known carnivorous dinosaurs. Titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
s were significant herbivores in its ancient ecosystems. Cretaceous sites are more common than Jurassic ones, but are often unable to be dated radiometrically
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
making it difficult to know their exact ages. Paleontologist Louis Jacobs, who spent time doing field work in Malawi
Malawi
The Republic of Malawi is a landlocked country in southeast Africa that was formerly known as Nyasaland. It is bordered by Zambia to the northwest, Tanzania to the northeast, and Mozambique on the east, south and west. The country is separated from Tanzania and Mozambique by Lake Malawi. Its size...
, says that African beds are "in need of more field work" and will prove to be a "fertile ground...for discovery."
Climate
The Triassic was generally dry, a trend that began in the late CarboniferousCarboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
, 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
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water—especially the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
s—experience less variation in temperature. Because much of the land that constituted Pangaea was distant from the oceans, temperatures fluctuated greatly, and the interior of Pangaea probably included expansive areas of desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
. Abundant evidence of red beds
Red beds
Red beds are sedimentary rocks, which typically consist of sandstone, siltstone, and shale that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of...
and evaporites such as salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
support these conclusions.
Sea levels began to rise during the Jurassic, which was probably caused by an increase in seafloor spreading
Seafloor spreading
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics....
. 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. Furthermore, Pangaea began to rift into smaller divisions, bringing more land area in contact with the ocean by forming the Tethys Sea
Tethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
. Temperatures continued to increase and began to stabilize. Humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
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
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
in the atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
are thought to have caused the world temperature gradient
Temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees per unit length...
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
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
. In fact, by the middle Cretaceous, equatorial ocean waters (perhaps as warm as 20°C in the deep ocean) may have been too warm for sea life, and land areas near the equator may have been deserts despite their proximity to water. The circulation of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
to the deep ocean may also have been disrupted. For this reason, large volumes of organic matter that was unable to decompose
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
accumulated, eventually being deposited as "black shale
Oil shale
Oil shale, an organic-rich fine-grained sedimentary rock, contains significant amounts of kerogen from which liquid hydrocarbons called shale oil can be produced...
".
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 cap
Polar ice cap
A polar ice cap is a high latitude region of a planet or natural satellite that is covered in ice. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of...
s and glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s, but there is no evidence of either. Quantitative models have also been unable to recreate the flatness of the Cretaceous temperature gradient.
The amount of oxygen in the Mesozoic atmosphere varied widely, but was significantly higher on average (~26%) than in today's atmosphere (20 to 21%).
Life
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
period allowed for the radiation
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...
of many new lifeforms. In particular, the extinction of the large herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
and carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
dinocephalia
Dinocephalia
Dinocephalia are a clade of large early therapsids that flourished during the Middle Permian, but became extinct leaving no descendants.-Description:...
left those ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s empty. Some were filled by the surviving cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
s and dicynodont
Dicynodont
Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
s, the latter of which subsequently became extinct. 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.
The dominant land plant species of the time were gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...
s, 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 species, the ginkgo biloba, is perceived to have evolved at this time and still exists today as the only surviving species from its phylum. As well, the extant genus sequoia
Sequoia (genus)
Sequoia is a genus of redwood coniferous trees in the Sequoioideae subfamily, of the Cupressaceae family. The only extant species of the genus is the Sequoia sempervirens in the Northern California coastal forests ecoregion of Northern California and Southern Oregon in the United States...
is believed to have evolved in the Mesozoic.
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 P-Tr extinction. Animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
life was then dominated by large archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
ian reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s: dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s, and aquatic reptiles such as ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
s, plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
s, and mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
s.
The climatic changes of the late Jurassic and Cretaceous provided for further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and placental mammal
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
s also appeared. Angiosperms
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
radiated sometime in the early Cretaceous, first in the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
, 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
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
was still dominated by cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
and fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s until after the KT extinction.
Some have argued that insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s diversified with angiosperms because insect anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
, especially the mouth
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of 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.
As the temperatures in the seas increased, the larger animals of the early Mesozoic gradually began to disappear while smaller animals of all kinds, including lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s, snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, and perhaps primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s, evolved. The KT extinction exacerbated this trend. The large archosaurs became extinct, while birds and mammals thrived, as they do today.