251.902–201.3 million years ago
|Mean atmospheric O|
2 content over period duration
|c. 16 vol %|
(80 % of modern level)
|Mean atmospheric CO|
2 content over period duration
|c. 1750 ppm |
(6 times pre-industrial level)
|Mean surface temperature over period duration||c. 17 °C|
(3 °C above modern level)
The Triassic ( // ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago (Mya), to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.
A system in stratigraphy is a unit of rock layers that were laid down together within the same corresponding geological period. The associated period is a chronological time unit, a part of the geological time scale, while the system is a unit of chronostratigraphy. Systems are unrelated to lithostratigraphy, which subdivides rock layers on their lithology. Systems are subdivisions of erathems and are themselves divided into series and stages.
The Permian is a geologic period and system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic period 251.902 Mya. It is the last period of the Paleozoic era; the following Triassic period belongs to the Mesozoic era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm.
The Jurassic period is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, and the Tithonian event at the end; however, neither event ranks among the "Big Five" mass extinctions.
Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.
The 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 and Triassic geologic periods, as well as between the Paleozoic and Mesozoic eras, approximately 252 million years ago. It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It was the largest known mass extinction of insects. Some 57% of all biological families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of land-dwelling life took significantly longer than after any other extinction event, possibly up to 10 million years. Studies in Bear Lake County, near Paris, Idaho, showed a relatively quick rebound in a localized marine ecosystem, taking around 2 million years to recover, suggesting that the impact of the extinction may have been felt less severely in some areas than others.
Therapsida is a group of synapsids that includes mammals and their ancestors. Many of the traits today seen as unique to mammals had their origin within early therapsids, including having their four limbs extend vertically beneath the body, as opposed to the sprawling posture of reptiles. The earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian.
Archosaurs are a group of diapsid amniotes whose living representatives consist of birds and crocodilians. This group also includes all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most recent common ancestor of living birds and crocodilians and all of its descendants. It includes two main clades: Pseudosuchia, which includes crocodilians and their extinct relatives, and Avemetatarsalia, which includes birds and their extinct relatives.
The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.
Mammals are vertebrate animals constituting the class Mammalia, and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals. The largest orders are the rodents, bats and Soricomorpha. The next three are the Primates, the Cetartiodactyla, and the Carnivora.
Pterosaurs were flying reptiles of the extinct clade or order Pterosauria. They existed during most of the Mesozoic: from the late Triassic to the end of the Cretaceous. Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically lengthened fourth finger.
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago, although the exact origin and timing of the evolution of dinosaurs is the subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago; their dominance continued through the Jurassic and Cretaceous periods. Reverse genetic engineering and the fossil record both demonstrate that birds are modern feathered dinosaurs, having evolved from earlier theropods during the late Jurassic Period. As such, birds were the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event 66 million years ago. Dinosaurs can therefore be divided into avian dinosaurs, or birds; and non-avian dinosaurs, which are all dinosaurs other than birds. This article deals primarily with non-avian dinosaurs.
The global climate during the Triassic was mostly hot and dry,with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic.
The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods,, and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas, a whole class (conodonts) and 23–34% of marine genera disappeared. On land, all archosaurs other than crocodylomorphs and Avemetatarsalia, some remaining therapsids, and many of the large amphibians became extinct.
The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers (tri meaning "three") that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias".
Friedrich August von Alberti was a German geologist whose ground-breaking 1834 publication recognized the unity of the three characteristic strata that compose the sedimentary deposits of the Triassic period in Northern Europe. From the fossils contained in the three distinct layers— of red bed sandstones, capped by limestones (Muschelkalk), followed by black shales— that are found throughout Germany and Northwest Europe, and are called the 'Trias', Alberti detected that they formed a single stratigraphic formation; today it would be termed a system. He identified the Triassic as bearing a unique fossil fauna, bounded by the Permian extinction below and by another extinction above.
Germany, officially the Federal Republic of Germany, is a country in Central and Western Europe, lying between the Baltic and North Seas to the north, and the Alps, Lake Constance and the High Rhine to the south. It borders Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, France to the southwest, and Luxembourg, Belgium and the Netherlands to the west.
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, Asia to the east, and the Mediterranean Sea to the south. It comprises the westernmost part of Eurasia.
The Triassic is usually separated into Early, Middle, and Late Triassic Epochs, and the corresponding rocks are referred to as Lower, Middle, or Upper Triassic. The faunal stages from the youngest to oldest are:
The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.902 Ma and 247.2 Ma. Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy. The Early Triassic is the oldest epoch of the Mesozoic Era and is divided into the Induan and Olenekian ages.
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 247.2 Ma and 237 Ma. The Middle Triassic is divided into the Anisian and Ladinian ages or stages.
The Late Triassic is the third and final of three epochs of the Triassic Period in the geologic timescale. The Triassic-Jurassic extinction event began during this epoch and is one of the five major mass extinction events of the Earth. The corresponding series is known as the Upper Triassic. In Europe the epoch was called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age. The Late Triassic spans the time between 237 Ma and 201.3 Ma. The Late Triassic is divided into the Carnian, Norian and Rhaetian ages.
|Upper/Late Triassic (Tr3)|
|Middle Triassic (Tr2)|
|Lower/Early Triassic (Scythian)|
During the Triassic, almost all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator and spanning from pole to pole, called Pangaea ("all the land"). From the east, along the equator, the Tethys sea penetrated Pangaea, causing the Paleo-Tethys Ocean to be closed.
Later in the mid-Triassic a similar sea penetrated along the equator from the west. The remaining shores were surrounded by the world-ocean known as Panthalassa ("all the sea"). All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates; thus, very little is known of the Triassic open ocean.
The supercontinent Pangaea was rifting during the Triassic—especially late in that period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangaea, which separated New Jersey from Morocco, are of Late Triassic age; in the U.S., these thick sediments comprise the Newark Group.
Because a super-continental mass has less shoreline compared to one broken up, Triassic marine deposits are globally relatively rare, despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west. Thus Triassic stratigraphy is mostly based on organisms that lived in lagoons and hypersaline environments, such as Estheria crustaceans.
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 time boundary separating the Permian and Triassic marks the advent of an extinction event with global impact, although African strata from this time period have not been thoroughly studied.
During the Triassic peneplains are thought to have formed in what is now Norway and southern Sweden.Remnants of this peneplain can be traced as a tilted summit accordance in the Swedish West Coast. In northern Norway Triassic peneplains may have been buried in sediments to be then re-exposed as coastal plains called strandflats. Dating of illite clay from a strandflat of Bømlo, southern Norway, have shown that landscape there became weathered in Late Triassic times (c. 210 million years ago) with the landscape likely also being shaped during that time.
At Paleorrota geopark, located in Rio Grande do Sul, Brazil, the Santa Maria Formation and Caturrita Formations are exposed. In these formations, one of the earliest dinosaurs, Staurikosaurus , as well as the mammal ancestors Brasilitherium and Brasilodon have been discovered.
The Triassic continental interior climate was generally hot and dry, so that typical deposits are red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole; in fact, the polar regions were apparently moist and temperate, providing a climate suitable for forests and vertebrates, including reptiles. Pangaea's large size limited the moderating effect of the global ocean; its continental climate was highly seasonal, with very hot summers and cold winters.The strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons.
The Triassic may have mostly been a dry period, but evidence exists that it was punctuated by several episodes of increased rainfall in tropical and subtropical latitudes of the Tethys Sea and its surrounding land.Sediments and fossils suggestive of a more humid climate are known from the Anisian to Ladinian of the Tethysian domain, and from the Carnian and Rhaetian of a larger area that includes also the Boreal domain (e.g., Svalbard Islands), the North American continent, the South China block and Argentina.
The best studied of such episodes of humid climate, and probably the most intense and widespread, was the Carnian Pluvial Event.
Three categories of organisms can be distinguished in the Triassic record: survivors from the Permian–Triassic extinction event, new groups which flourished briefly, and other new groups which went on to dominate the Mesozoic Era.
On land, the surviving vascular plants included the lycophytes, the dominant cycadophytes, ginkgophyta (represented in modern times by Ginkgo biloba ), ferns, horsetails and glossopterids. The spermatophytes, or seed plants, came to dominate the terrestrial flora: in the northern hemisphere, conifers, ferns and bennettitales flourished. Glossopteris (a seed fern) was the dominant southern hemisphere tree during the Early Triassic period.
Before the Permian extinction, Archaeplastida (red and green algae) had been the major marine phytoplanktons since about 659–645 million years ago,when they replaced marine planktonic cyanobacteria, which first appeared about 800 million years ago, as the dominant phytoplankton in the oceans. In the Triassic, secondary endosymbiotic algae became the most important plankton.
In marine environments, new modern types of corals appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of Devonian or modern times. Serpulids appeared in the Middle Triassic.Microconchids were abundant. The shelled cephalopods called ammonites recovered, diversifying from a single line that survived the Permian extinction.
The fish fauna was remarkably uniform, suggesting that very few families survived the Permian extinction. There were also many types of marine reptiles. These included the Sauropterygia, which featured pachypleurosaurus and nothosaurs (both common during the Middle Triassic, especially in the Tethys region), placodonts, and the first plesiosaurs. The first of the lizardlike Thalattosauria (askeptosaurs) and the highly successful ichthyosaurs, which appeared in Early Triassic seas soon diversified, and some eventually developed to huge size during the Late Triassic. Subequatorial saurichthyids have also been described in Early Triassic strata.
Groups of terrestrial fauna, which appeared in the Triassic period or achieved a new level of evolutionary success during it include:
The Permian–Triassic extinction devastated terrestrial life. Biodiversity rebounded as the surviving species repopulated empty terrain, but these were short-lived. Diverse communities with complex food-web structures took 30 million years to reestablish.
Temnospondyl amphibians were among those groups that survived the Permian–Triassic extinction; some lineages (e.g. trematosaurs) flourished briefly in the Early Triassic, while others (e.g. capitosaurs) remained successful throughout the whole period, or only came to prominence in the Late Triassic (e.g. plagiosaurs, metoposaurs). As for other amphibians, the first Lissamphibia, progenitors of first frogs, are known from the Early Triassic, but the group as a whole did not become common until the Jurassic, when the temnospondyls had become very rare. Other survivors the Chroniosuchia and Embolomeri were more closely related to amniotes than temnospondyls. Those became extinct after some million years.
Most of the Reptiliomorpha, stem-amniotes that gave rise to the amniotes, disappeared in Triassic, but two water-dwelling groups survived; Embolomeri that only survived into the early part of the period, and the Chroniosuchia, which survived until the end of Triassic.
Archosauromorph reptiles, especially archosaurs, progressively replaced the synapsids that had dominated the previous Permian period. The Cynognathus was the characteristic top predator in earlier Triassic (Olenekian and Anisian) on Gondwana. Both kannemeyeriid dicynodonts and gomphodont cynodonts remained important herbivores during much of the period, and ecteniniids played a role as large-sized, cursorial predators in the Late Triassic. During the Carnian (early part of the Late Triassic), some advanced cynodonts gave rise to the first mammals. At the same time the Ornithodira, which until then had been small and insignificant, evolved into pterosaurs and a variety of dinosaurs. The Crurotarsi were the other important archosaur clade, and during the Late Triassic these also reached the height of their diversity, with various groups including the phytosaurs, aetosaurs, several distinct lineages of Rauisuchia, and the first crocodylians (the Sphenosuchia). Meanwhile, the stocky herbivorous rhynchosaurs and the small to medium-sized insectivorous or piscivorous Prolacertiformes were important basal archosauromorph groups throughout most of the Triassic.
Among other reptiles, the earliest turtles, like Proganochelys and Proterochersis , appeared during the Norian Age (Stage) of the Late Triassic Period. The Lepidosauromorpha, specifically the Sphenodontia, are first found in the fossil record of the earlier Carnian Age. The Procolophonidae were an important group of small lizard-like herbivores.
During the Triassic, archosaurs displaced therapsids as the dominant amniotes. This "Triassic Takeover" may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammaliaform successors to live as small, mainly nocturnal insectivores. Nocturnal life may have forced the mammaliaforms to develop fur and a higher metabolic rate.
The Monte San Giorgio lagerstätte, now in the Lake Lugano region of northern Italy and Switzerland, was in Triassic times a lagoon behind reefs with an anoxic bottom layer, so there were no scavengers and little turbulence to disturb fossilization, a situation that can be compared to the better-known Jurassic Solnhofen Limestone lagerstätte.
The remains of fish and various marine reptiles (including the common pachypleurosaur Neusticosaurus, and the bizarre long-necked archosauromorph Tanystropheus ), along with some terrestrial forms like Ticinosuchus and Macrocnemus , have been recovered from this locality. All these fossils date from the Anisian/Ladinian transition (about 237 million years ago).
The Triassic period ended with a mass extinction, which was particularly severe in the oceans; the conodonts disappeared, as did all the marine reptiles except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods, gastropods, and molluscs were severely affected. In the oceans, 22% of marine families and possibly about half of marine genera went missing.
Though the end-Triassic extinction event was not equally devastating in all terrestrial ecosystems, several important clades of crurotarsans (large archosaurian reptiles previously grouped together as the thecodonts) disappeared, as did most of the large labyrinthodont amphibians, groups of small reptiles, and some synapsids (except for the proto-mammals). Some of the early, primitive dinosaurs also became extinct, but more adaptive ones survived to evolve into the Jurassic. Surviving plants that went on to dominate the Mesozoic world included modern conifers and cycadeoids.
The cause of the Late Triassic extinction is uncertain. It was accompanied by huge volcanic eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago (40Ar/39Ar dates), 201.3 Mya. Both dates are gaining accuracy by using more accurate forms of radiometric dating, in particular the decay of uranium to lead in zircons formed at time of the impact. So, the evidence suggests the Manicouagan impact preceded the end of the Triassic by approximately 10±2 Ma. It could not therefore be the immediate cause of the observed mass extinction.forming the Central Atlantic Magmatic Province (CAMP), one of the largest known inland volcanic events since the planet had first cooled and stabilized. Other possible but less likely causes for the extinction events include global cooling or even a bolide impact, for which an impact crater containing Manicouagan Reservoir in Quebec, Canada, has been singled out. However, the Manicouagan impact melt has been dated to 214±1 Mya. The date of the Triassic-Jurassic boundary has also been more accurately fixed recently, at
The number of Late Triassic extinctions is disputed. Some studies suggest that there are at least two periods of extinction towards the end of the Triassic, separated by 12 to 17 million years. But arguing against this is a recent study of North American faunas. In the Petrified Forest of northeast Arizona there is a unique sequence of late Carnian-early Norian terrestrial sediments. An analysis in 2002 found no significant change in the paleoenvironment.Phytosaurs, the most common fossils there, experienced a change-over only at the genus level, and the number of species remained the same. Some aetosaurs, the next most common tetrapods, and early dinosaurs, passed through unchanged. However, both phytosaurs and aetosaurs were among the groups of archosaur reptiles completely wiped out by the end-Triassic extinction event.
It seems likely then that there was some sort of end-Carnian extinction, when several herbivorous archosauromorph groups died out, while the large herbivorous therapsids—the kannemeyeriid dicynodonts and the traversodont cynodonts—were much reduced in the northern half of Pangaea (Laurasia).
These extinctions within the Triassic and at its end allowed the dinosaurs to expand into many niches that had become unoccupied. Dinosaurs became increasingly dominant, abundant and diverse, and remained that way for the next 150 million years. The true "Age of Dinosaurs" is during the following Jurassic and Cretaceous periods, rather than the Triassic.
An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the threshold chosen for describing an extinction event as "major", and the data chosen to measure past diversity.
The Mesozoic Era is an interval of geological time from about. It is also called the Age of Reptiles and the Age of Conifers.
The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 541 million years to the present, and began with the Cambrian Period when animals first developed hard shells preserved in the fossil record. Its name was derived from the Ancient Greek words φανερός and ζωή, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon. The term "Phanerozoic" was coined in 1930 by the American geologist George Halcott Chadwick (1876–1953). The time before the Phanerozoic, called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.
Synapsids (Greek: 'fused arch'; synonymous with theropsids –not to be confused with therapsids, which are a subordinate group to synapsids– are a group of animals that includes mammals and every animal more closely related to mammals than to the other members, reptiles and birds, included in the amniotes clade. They are easily separated from other amniotes by having a temporal fenestra, an opening low in the skull roof behind each eye, leaving a bony arch beneath each; this accounts for their name. Primitive synapsids are usually called pelycosaurs or pelycosaur-grade synapsids. This informal term consists of all synapsids which are not therapsids, a monophyletic more advanced mammal-like group. The non-mammalian synapsids are described as mammal-like reptiles in classical systematics; they can also be called stem mammals or proto-mammals. Synapsids evolved from basal amniotes and are one of the two major groups of the later amniotes, the other being the sauropsids, a group that includes modern reptiles and birds. The distinctive temporal fenestra developed in the ancestral synapsid about 312 million years ago, during the Late Carboniferous period.
The Siberian Traps is a large region of volcanic rock, known as a large igneous province, in Siberia, Russia. The massive eruptive event that formed the traps is one of the largest known volcanic events in the last 500 million years.
Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to 2011, the clade Pseudosuchia was often called Crurotarsi in reference to the crurotarsal ankle found in almost all members of the group, which traditionally included phytosaurs, ornithosuchids, and suchians. However, a major 2011 study of Triassic archosaur relations proposed that phytosaurs were not closely related to other traditional "crurotarsans", at least compared to "bird-line archosaurs" (Avemetatarsalians) such as pterosaurs and dinosaurs. As a result, the possession of a crurotarsal ankle was considered a plesiomorphic ("primitive") feature retained by pseudosuchians. Crurotarsi now refers to a broader group of reptiles including Pseudosuchia, Phytosauria, and Avemetatarsalia. Despite Pseudosuchia meaning "false crocodiles", the name is a misnomer as true crocodilians are a subset of the group.
The geological history of Earth follows the major events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.
The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a Late Anisian to Early Norian age, and is notable for its fossils of early dinosaurs, including the herrerasaur Staurikosaurus, the basal saurischian Teyuwasu, and the basal sauropodomorph Saturnalia. It received this name because it was discovered first in the city of Santa María.
Gondwana, , was a supercontinent that existed from the Neoproterozoic until the Jurassic.
A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes, some are just a collection of small microcontinents while others are large conglomerates of crust. As time progresses and sea levels rise and fall more crust can be exposed making way for larger landmasses. The continents of the past shaped the evolution of organisms on Earth and contributed to the climate of the globe as well. As land masses break apart, species are separated and those that were once the same now have evolved to their new climate. The constant movement of these landmasses greatly determines the distribution of organisms on the Earth's surface. This is evident with how similar fossils are found on completely separate continents. Also, as continents move, mountain building events (orogenies) occur, causing a shift in the global climate as new rock is exposed and then there is more exposed rock at higher elevations. This causes glacial ice expansion and an overall cooler global climate. Which effects the overall global climate trend of the Earth. The movement of the continents greatly affects the overall dispersal of organisms throughout the world and the trend in climate throughout the Earth's history. Examples include Laurentia, Baltica and Avalonia, which collided together during the Caledonian orogeny to form the Old Red Sandstone paleocontinent of Laurussia. Another example includes a collision that occurred during the late Pennsylvanian and early Permian time when there was a collision between the two continents of Tarimsky and Kirghiz-Kazakh. This collision was caused because of their askew convergence when the paleoceanic basin closed.
Reptiles arose about 310–320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds and mammals that are descended from early reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.
The prehistory of the United States comprises the occurrences within regions now part of the United States of America during the interval of time spanning from the formation of the Earth to the documentation of local history in written form. At the start of the Paleozoic era, what is now "North" America was actually in the southern hemisphere. Marine life flourished in the country's many seas, although terrestrial life had not yet evolved. During the latter part of the Paleozoic, seas were largely replaced by swamps home to amphibians and early reptiles. When the continents had assembled into Pangaea drier conditions prevailed. The evolutionary precursors to mammals dominated the country until a mass extinction event ended their reign.
Gracilisuchidae is an extinct family of suchian archosaurs known from the early Middle Triassic to the early Late Triassic of China and Argentina.
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