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The Mesozoic Era ( ), also called the Age of Reptiles and the Age of Conifers, is the second-to-last
era An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth. Compar ...
of Earth's
geological history
geological history
, lasting from about and comprising the
Triassic The Triassic ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions int ...

Triassic
,
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and
Cretaceous The Cretaceous ( ) is a that lasted from about 145 to 66 (Mya). It is the third and final period of the , as well as the longest. At around 79 million years, it is the longest geological period of the entire . The name is derived from the Latin ...

Cretaceous
Periods. It is characterized by the dominance of archosaurian
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

reptile
s, like the
dinosaur Dinosaurs are a diverse group of reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) an ...

dinosaur
s; an abundance of
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ex ...
s and
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses and other bryophytes by being vascular, ...

fern
s; a hot
greenhouse '' (giant Amazon waterlilies) in a large greenhouse at the Saint Petersburg Botanical Garden. A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent mater ...
climate; and the
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building A mountain is an elevated portion of the Earth's crust, gene ...
break-up of
Pangaea Pangaea or Pangea () was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology) ...

Pangaea
. The Mesozoic is the middle of three eras since complex life evolved: the
Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popula ...
, the Mesozoic, and the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the ge ...

Cenozoic
. The era began in the wake of the
Permian–Triassic extinction event The Permian–Triassic extinction event, also known as the P–Tr extinction, the P–T extinction, the End-Permian Extinction, and colloquially as the Great Dying, formed the boundary between the Permian The Permian ( ) is a geologic period ...
, the largest well-documented
mass extinction An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity Biodiversity is the biological variety and Genetic variability, variability of life, life on Earth. Biodiversity is ...
in Earth's history, and ended with the
Cretaceous–Paleogene extinction event near Drumheller Drumheller is a town within the Red Deer River The Red Deer River is a river in Alberta ("Strong and free") , image_map = Alberta in Canada 2.svg , Label_map = yes , coordinates ...
, another mass extinction whose victims included the non-avian dinosaurs. The Mesozoic was a time of significant tectonic, climatic, 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. Archaic
bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwide and range in size from the to the . There ar ...

bird
s appeared in the Jurassic, having
evolved Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...
from a branch of
theropod Theropoda ( from Ancient Greek, Greek 'wild beast' and 'foot'), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three-toed limbs. Theropods are generally classed as a group of saurischian d ...

theropod
dinosaurs, then
true toothless birds
true toothless birds
appeared in the Cretaceous. The first
mammal Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republ ...
s also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic. The
flowering plants The flowering plants, also known as Angiospermae (), or Magnoliophyta (), are the most diverse group of land plants The Embryophyta () or land plants are the most familiar group of green plants that form vegetation on earth. Embryophyta is a c ...

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


Naming

The phrase "Age of Reptiles" was introduced by the 19th century
paleontologist Paleontology, also spelled palaeontology or palæontology (), is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch (roughly 11,700 years before present). It includes the study of Fossil, ...
Gideon Mantell Gideon Algernon Mantell MRCS Fellow of the Royal Society, FRS (3 February 1790 – 10 November 1852) was an English obstetrician, geologist and paleontology, palaeontologist. His attempts to reconstruct the structure and life of ''Iguanodon'' be ...

Gideon Mantell
who viewed it as dominated by
diapsid Diapsids ("two arches") are a group of amniote tetrapods that developed two holes (temporal fenestra) in each side of their skulls about 300 million years ago during the late Carboniferous period. The diapsids are extremely diverse, and include all ...

diapsid
s such as ''
Iguanodon ''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of ornithopod dinosaur that existed roughly halfway between the first of the swift bipedal hypsilophodontids of the mid-Jurassic and the duck-billed dinosaurs of the late Creta ...

Iguanodon
'', ''
Megalosaurus ''Megalosaurus'' (meaning "great lizard", from Greek , ', meaning 'big', 'tall' or 'great' and , ', meaning 'lizard') is an extinct genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classifica ...

Megalosaurus
'', ''
Plesiosaurus ''Plesiosaurus'' (Greek: ' ('), near to + ' ('), lizard) is a genus of extinct, large marine sauropterygian reptile that lived during the early part of the Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigrap ...

Plesiosaurus
'', and ''
Pterodactylus ''Pterodactylus'' (from Greek language, Greek πτεροδάκτυλος, ''pterodaktulos'', meaning "winged finger") is an extinct genus of pterosaurs, whose members are commonly known as pterodactyls (). It is thought to contain only a single ...

Pterodactylus
''. The current name was proposed in 1840 by the British geologist
John Phillips
John Phillips
(1800–1874). "Mesozoic" literally means 'middle life', deriving from the
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
prefix ( 'between') and ( 'animal, living being'). In this way, the Mesozoic is comparable to the Cenozoic () and Paleozoic ('old life') Eras as well as the
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 541million years ago. It is the most recent part of the Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part ...
('earlier life') Eon. The Mesozoic Era was originally described as the "secondary" era, following the "primary" (
Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popula ...
), and preceding the
Tertiary Tertiary ( ) is a widely used but obsolete term for the Period (geology), geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-bird, avian dinosaurs in the Cretaceous–Paleogene extincti ...

Tertiary
.


Geologic periods

Following the Paleozoic, the Mesozoic extended roughly 186 million years, from when the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the ge ...

Cenozoic
Era began. This time frame is separated into three geologic periods. From oldest to youngest: *
Triassic The Triassic ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions int ...

Triassic
() *
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
() *
Cretaceous The Cretaceous ( ) is a that lasted from about 145 to 66 (Mya). It is the third and final period of the , as well as the longest. At around 79 million years, it is the longest geological period of the entire . The name is derived from the Latin ...

Cretaceous
() The lower boundary of the Mesozoic is set by the
Permian–Triassic extinction event The Permian–Triassic extinction event, also known as the P–Tr extinction, the P–T extinction, the End-Permian Extinction, and colloquially as the Great Dying, formed the boundary between the Permian The Permian ( ) is a geologic period ...
, during which it has been estimated that up to 90-96% of marine species became
extinct Extinction is the termination of a kind of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by ...

extinct
although those approximations have been brought into question with some paleontologists estimating the actual numbers as low as 81%. 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 near Drumheller Drumheller is a town within the Red Deer River The Red Deer River is a river in Alberta ("Strong and free") , image_map = Alberta in Canada 2.svg , Label_map = yes , coordinates ...
(or K–Pg extinction event), which may have been caused by an asteroid impactor that created
Chicxulub Crater The Chicxulub crater (; ) is an impact crater buried underneath the Yucatán Peninsula in Mexico Mexico ( es, México ; Nahuan languages: ), officially the United Mexican States (; EUM ), is a List of sovereign states, country in the s ...

Chicxulub Crater
on the
Yucatán Peninsula The Yucatán Peninsula (, also , ; es, Península de Yucatán), in southeastern Mexico, separates the Caribbean Sea from the Gulf of Mexico, with the northern coastline on the Yucatán Channel. The peninsula lies east of the Isthmus of Tehuantep ...

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
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 The Triassic–Jurassic (Tr-J) extinction event, sometimes called the end-Triassic extinction, marks the boundary between the Triassic The Triassic ( ) is a geologic period and system A system is a group of Interaction, interacting or interrel ...
, two of the "
big fiveBig Five may refer to: Animals * the Big five game, Big Five, large African wild animals said to be most difficult to hunt: lion, leopard, rhinoceros, elephant and Cape buffalo * Big Five animals of the Kaziranga National Park, Assam, India: Ind ...
", and it is divided into three major epochs: Early, Middle, and Late Triassic. 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 ''Lystrosaurus'' (; 'shovel lizard'; proper Greek is λίστρον ''lístron'' ‘tool for leveling or smoothing, shovel, spade, hoe’) was a herbivorous genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice a ...

Lystrosaurus
'',
labyrinthodont Labyrinthodontia (Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mil ...
s, and ''
Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W.K. Parker) is an Extinction, extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and ...

Euparkeria
'' along with many other creatures that managed to survive the Permian extinction.
Temnospondyl Temnospondyli (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 ...
s evolved during this time and would be the dominant predator for much of the Triassic. The Middle Triassic, from 247 to 237 million years ago, featured the beginnings of the breakup of Pangaea and the opening of the
Tethys Ocean The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was an ocean during much of the Era located between the ancient continents of and , before the opening of the and oceans during the Period. Etym ...
. Ecosystems had recovered from the Permian extinction. Algae, sponge, corals, and crustaceans all had recovered, and new aquatic reptiles evolved, such as
ichthyosaur Ichthyosaurs (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Myce ...
s and
nothosaur Nothosaurs (order Nothosauroidea) were Triassic The Triassic ( ) is a geologic period and system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system ...
s. 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. Following the bloom of the Middle Triassic, the Late Triassic, from 237 to 201 million years ago, featured frequent heat spells and moderate precipitation (10–20 inches per year). The recent warming led to a boom of dinosaurian evolution on land as those one began to separate from each other (Nyasasaurus from 243 to 210 million years ago, approximately 235–30 ma, some of them separated into Sauropodomorphs, Theropods and Herrerasaurids), as well as the first
pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") were flying reptiles of the extinct clade or Order (biology), order Pterosauria. They existed during most of the Mesozoic: from the late Triassic to the end of the Cretace ...
s. During the Late Triassic, some advanced
cynodont The cynodonts ("dog teeth") (clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancestor and all ...

cynodont
s gave rise to the first
Mammaliaformes Mammaliaformes ("mammal-shaped") is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancestor ...

Mammaliaformes
. All this climatic change, however, resulted in a large die-out known as the Triassic–Jurassic extinction event, in which many
archosaurs Archosauria ("ruling reptiles") is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancestor an ...
(excluding pterosaurs, dinosaurs and
crocodylomorph Crocodylomorpha is a group of archosaur Archosauria ("ruling reptiles") is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of term which i ...

crocodylomorph
s), most
synapsid Synapsids are a group of animals that includes mammals and every animal more closely related to mammals than to the other members of the amniote clade, such as reptiles and birds. Unlike other amniotes, they have a Skull#Fenestrae, temporal fenes ...

synapsid
s, 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; 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. The Early Jurassic spans from 200 to 175 million years ago. The climate was tropical and much more humid than the Triassic, as a result of the large seas appearing between the land masses. In the oceans,
plesiosaurs The Plesiosauria (; Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 ...
, ichthyosaurs and
ammonites Ammonoids are a group of extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Li ...

ammonites
were abundant. On land, dinosaurs and other archosaurs staked their claim as the dominant race, with
theropods Theropoda ( from Greek 'wild beast' and 'foot'), whose members are known as theropods, is a dinosaur Dinosaurs are a diverse group of reptiles of the clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyleti ...

theropods
such as ''
Dilophosaurus ''Dilophosaurus'' ( ) is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 193 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserved ...

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 ''Castorocauda'' is an extinct, semi-aquatic, beaver Beavers are large, semiaquatic rodents in the genus ''Castor'' native to the temperate Northern Hemisphere. There are two extant species: the North American beaver (''Castor canade ...
'', for example, had adaptations for swimming, digging and catching fish. ''
Fruitafossor ''Fruitafossor'' was a termite Termites are Eusociality, eusocial insects that are classified at the Taxonomy (biology), taxonomic rank of infraorder Isoptera, or as Taxonomic rank#All ranks, epifamily Termitoidae within the order Blattodea (a ...
'', 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
termite Termites are Eusociality, eusocial insects that are classified at the Taxonomy (biology), taxonomic rank of infraorder Isoptera, or alternatively as Taxonomic rank#All ranks, epifamily Termitoidae, within the order Blattodea (along with cockroa ...

termite
s, as ants had not yet appeared). The first
multituberculates Multituberculata (commonly known as multituberculates, named for the multiple tubercle Image:Mammillaria marksiana.jpg, 250px, This view of the cactus ''Mammillaria marksiana'' shows its pattern of prominent tubercles, with the spines emanating fr ...
like '' Rugosodon'' evolved, while
volaticotheria Volaticotherini is a clade of eutriconodont mammals from the Mesozoic. In addition to the type genus ''Volaticotherium'', it includes the genera ''Argentoconodon'', ''Ichthyoconodon'', and potentially ''Triconolestes''. Since most remains are pr ...
ns took to the skies. The Middle Jurassic spans from 175 to 163 million years ago. During this epoch, dinosaurs flourished as huge herds of sauropods, such as ''
Brachiosaurus ''Brachiosaurus'' () is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classificatio ...

Brachiosaurus
'' and ''
Diplodocus ''Diplodocus'' (, , or ) is a genus of diplodocid sauropod dinosaurs, whose fossils were first discovered in 1877 by Samuel Wendell Williston, S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a New Latin, neo-Lati ...

Diplodocus
'', filled the fern prairies, chased by many new predators such as ''
Allosaurus ''Allosaurus'' () is a genus of large carnivorous theropoda, theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic Epoch (geology), epoch (Kimmeridgian to late TithonianTurner, C.E. and Peterson, F., (1999). ...

Allosaurus
''.
Conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ex ...
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. The Late Jurassic spans from 163 to 145 million years ago. During this epoch, the first
avialan Avialae ("bird wings") is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancestor and all it ...
s, like ''
Archaeopteryx ''Archaeopteryx'' ( "old wing"), sometimes referred to by its German name, ' ("original bird" or "first bird"), is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of thi ...

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


Cretaceous

The Cretaceous is the longest period of the Mesozoic, but has only two epochs: Early and Late Cretaceous. The Early Cretaceous spans from 145 to 100 million years ago. The Early Cretaceous saw the expansion of seaways, and as a result, the decline and/or extinction of Laurasian sauropods. Some island-hopping dinosaurs, like ''
Eustreptospondylus ''Eustreptospondylus'' ( ; meaning "true ''Streptospondylus''") is a genus of megalosaurid Theropoda, theropod dinosaur, from the Oxfordian stage of the Late Jurassic period (some time between 163 and 154 million years ago) in southern Engla ...

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 ''Carcharodontosaurus'' is a genus of large carcharodontosaurid Carcharodontosaurids (from the Greek language, Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") were a group of carnivorous thero ...

Carcharodontosaurus
'' and ''
Spinosaurus ''Spinosaurus'' (meaning "spine lizard") is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classificati ...

Spinosaurus
''. Seasons came back into effect and the poles got seasonally colder, but some dinosaurs still inhabited the polar forests year round, such as '''' and ''
Muttaburrasaurus ''Muttaburrasaurus'' was a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also r ...
''. The poles were too cold for crocodiles, and became the last stronghold for large amphibians like ''
Koolasuchus ''Koolasuchus'' is an extinct genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may als ...

Koolasuchus
''. Pterosaurs got larger as genera like '' Tapejara'' and '''' evolved. Mammals continued to expand their range:
eutriconodont Eutriconodonta is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, ...
s produced fairly large,
wolverine The wolverine () (also spelled wolverene), ''Gulo gulo'' (''Gulo'' is Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area aro ...

wolverine
-like predators like ''
Repenomamus ''Repenomamus'' is a genus of opossum-sized to badger-sized gobiconodontid mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by t ...
'' and ''
Gobiconodon ''Gobiconodon'' is an extinct genus of carnivorous mammal from the early Cretaceous. It weighed and measured . It was one of the largest mammals known from the Mesozoic. Like other gobiconodontidae, gobiconodontids, it possesses several speciation ...

Gobiconodon
'', early
theria Theria (; Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximatel ...
ns began to expand into
metatheria Metatheria is a mammalian clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All or ...
ns and
eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all Theria, therian mammals that are more closely related to Placentalia, placentals than to Marsupial, marsupials. Eutherians are distinguished from noneuther ...

eutheria
ns, and cimolodont
multituberculate Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct taxon of rodent-like allotherian mammals that existed for approximately 166 million years, the longest fossil history of any ...
s 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 The Cenozoic ( ; ) is Earth's current geological era An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the ge ...

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 ''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosau ...

Tyrannosaurus
'', ''
Ankylosaurus ''Ankylosaurus'' is a genus of Thyreophora, armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period (geology), Period, about 68–66 million years ago, in western North America, mak ...

Ankylosaurus
'', ''
Triceratops ''Triceratops'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refe ...

Triceratops
'' and
hadrosaurs Hadrosaurids ( el, ἁδρός, ''hadrós'', "stout, thick"), or duck-billed dinosaur Dinosaurs are a diverse group of reptiles of the clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural gr ...
dominated the food web. In the oceans,
mosasaurs Mosasaurs (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roma ...

mosasaurs
ruled, filling the role of the ichthyosaurs, which, after declining, had disappeared in the
Cenomanian-Turonian boundary event The Cenomanian-Turonian boundary event, or the Cenomanian-Turonian extinction event, the Cenomanian-Turonian anoxic event (Anoxic event, OAE 2), and referred also as the Bonarelli event, was one of two Anoxic event, anoxic extinction events in the ...
. Though
pliosaur Pliosauroidea is an extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biol ...
s had gone extinct in the same event, long-necked plesiosaurs such as ''
Elasmosaurus ''Elasmosaurus'' (;) is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also re ...
'' 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 Enantiornithes is a group of extinct Avialae, avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern ...
and ornithurine forms. Though mostly small, marine
hesperornithes Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by f ...
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 ''Didelphodon'' (from ''is''/nowiki>.html" ;"title="/nowiki>''is''/nowiki>">/nowiki>''is''/nowiki> "opossum" plus "tooth") is a genus of stagodont metatherians from the Late Cretaceous The Cretaceous (, ) is a geological period that lasted f ...

Didelphodon
'' and ''
Schowalteria ''Schowalteria'' is a genus of extinct mammal from the Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from plac ...
''. 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 Cretaceous–Paleogene extinction event, 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. Everything over 10 kilograms became extinct.


Paleogeography and tectonics

Compared to the vigorous convergent plate orogeny, 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 Range, 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 Craton, North China and Siberian cratons under the Pacific Ocean. 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 East Coast of the United States, U.S. East Coast) today. 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 South Asia, 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. 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 above today's sea level, flooding coastal areas. Furthermore, Pangaea began to rift into smaller divisions, creating new shoreline around the Tethys Ocean. Temperatures continued to increase, then began to stabilize. Humidity also increased with the proximity of water, and deserts retreated. The climate of the Cretaceous is less certain and more widely disputed. Probably, higher levels of carbon dioxide in the Earth's atmosphere, atmosphere are thought to have almost eliminated the north–south temperature gradient: temperatures were about the same across the planet, and about 10°Celsius, C higher than today. The circulation of oxygen to the deep ocean may also have been disrupted, preventing the decomposition of large volumes of organic matter, which was eventually deposition (sediment), deposited as "Oil shale, black shale". 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, Jurassic and Cretaceous.


Life


Flora

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. The earliest members of the genus ''Ginkgo'' first appeared during the Middle Jurassic. This genus is represented today by a single species, ''Ginkgo biloba''. The extant taxon, extant genus ''sequoia (genus), Sequoia'' is believed to have evolved in the Mesozoic. Bennettitales, an extinct group of gymnosperms with foliage superficially resembling that of cycads gained a global distribution during the Late Triassic, and represented one of the most common groups of Mesozoic seed plants. Flowering plants radiated during 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 (ecology), biomass was still dominated by cycads and
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses and other bryophytes by being vascular, ...

fern
s 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.C.Michael Hogan. 2010
''Fern''. Encyclopedia of Earth. National council for Science and the Environment
. Washington, DC


Fauna

The extinction of nearly all animal species at the end of the Permian Period allowed for the adaptive radiation, radiation of many new lifeforms. In particular, the extinction of the large herbivore, herbivorous pareiasaurs and carnivore, carnivorous gorgonopsians left those ecological niches empty. Some were filled by the surviving
cynodont The cynodonts ("dog teeth") (clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancestor and all ...

cynodont
s and dicynodonts, the latter of which subsequently became extinct. Recent research indicates that it took much longer for the reestablishment of complex ecosystems with high biodiversity, complex food webs, and specialized animals in a variety of niches, beginning in the mid-Triassic 4 million to 6 million years after the extinction, and not fully proliferated until 30 million years after the extinction. Animal life was then dominated by various archosaurs:
dinosaur Dinosaurs are a diverse group of reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) an ...

dinosaur
s, 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
bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwide and range in size from the to the . There ar ...

bird
s and
eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all Theria, therian mammals that are more closely related to Placentalia, placentals than to Marsupial, marsupials. Eutherians are distinguished from noneuther ...

eutheria
n 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

*


References

*''British Mesozoic Fossils'', 1983, The Natural History Museum, London.


External links


Mesozoic (chronostratigraphy scale)
{{Authority control Mesozoic, Geological eras