Chronologically, the Triassic Period is divided into three epochs: (i) theEarly Triassic, (ii) theMiddle Triassic, and (iii) theLate Triassic. The Triassic Period began after thePermian–Triassic extinction event that much reduced thebiosphere of planet Earth. The fossil record of the Triassic Period presents three categories of organisms: (i) animals that survived the Permian–Triassic extinction event, (ii) new animals that briefly flourished in the Triassic biosphere, and (iii) new animals that evolved and dominated theMesozoic Era.Reptiles, especiallyarchosaurs, were the chief terrestrial vertebrates during this time. A specialized group of archosaurs, calleddinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.[11] Archosaurs that became dominant in this period were primarilypseudosuchians, relatives and ancestors of moderncrocodilians, while some archosaurs specialized in flight, the first time among vertebrates, becoming thepterosaurs.Therapsids, the dominant vertebrates of the preceding Permian period, saw a brief surge in diversification in the Triassic, withdicynodonts andcynodonts quickly becoming dominant, but they declined throughout the period with the majority becoming extinct by the end. However, the first stem-groupmammals (mammaliamorphs), themselves a specialized subgroup of cynodonts, appeared during the Triassic and would survive the extinction event, allowing them to radiate during the Jurassic.Amphibians were primarily represented by thetemnospondyls, giant aquatic predators that had survived the end-Permian extinction and saw a new burst of diversification in the Triassic, before going extinct by the end; however, early crown-grouplissamphibians (including stem-groupfrogs,salamanders andcaecilians) also became more common during the Triassic and survived the extinction event. The earliest knownneopterygian fish, including earlyholosteans andteleosts, appeared near the beginning of the Triassic, and quickly diversified to become among the dominant groups of fish in both freshwater and marine habitats.
The vastsupercontinent ofPangaea dominated the globe during the Triassic, but in the latest Triassic (Rhaetian) and Early Jurassic it began to gradually rift into two separate landmasses:Laurasia to the north andGondwana to the south. The global climate during the Triassic was mostly hot and dry,[12] 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, theTriassic–Jurassic extinction event, that wiped out many groups, including most pseudosuchians, and allowed dinosaurs to assume dominance in the Jurassic.
View of the Tethys area during the Ladinian stage (230 Ma)230 Ma continental reconstruction
At the beginning of the Triassic, all the major continents were amalgamated into the supercontinent of Pangea. Centred on the equator, this stretched in an arc from the north to south polar regions withLaurussia in the north and Gondwana in the south. ThePaleo- andNeo-Tethys oceans lay within the arc of the supercontinent with the vastPanthalassa Ocean beyond.[14]North China andAmuria, andSouth China were separated from Pangea by the Paleoasian Ocean, but this closed by the Late Triassic.[15]
Pangea was surrounded bysubduction zones that dipped beneath the supercontinent. The great mountain ranges that marked the Late Paleozoic continental collisions were largely eroded and were being replaced by regions of thinned crust that lay along the lines of the futureAtlantic,Indian andSouthern oceans.[14][16]
The supercontinent changed motion from drifting westward to rotating counterclockwise during late Permian. This continued until the Carnian (c. 230 Ma), after which it resumed the westward motion. These changes in motion were triggered by the opening of the Neo-Tethys, and closing of the Paleo-Tethys respectively, and affected tectonic regimes particularly along the southern and western margins.[17]
The narrowCimmerianterranes that had rifted from the northern margin of Gondwana in the Permian continued to drift northwards; the Paleo-Tethys Ocean closing in front of them and the Neo-Tethys opening behind.[15]
In northern-eastern Pangea, the Siberian Traps LIP continued to erupt into the Middle Triassic. Lower Triassic major deltaic systems (including theTriassic Boreal Ocean delta plain)[19] advanced across the shallowArctic Ocean. Theircatchment areas the high ground of theUrals,Fennoscandinavia, the Canada-Greenland Shield and the Lomonosov High.[14] During the Late Triassic, in response to the opening of the Central Atlantic to the south, tectonic movements between North America andBaltica led to convergence in the High Arctic with uplift, folding and thrusting in theBarents Sea and North Siberian margin.[14]
Majorextensional tectonic movements, that began in the late Permian, continued across Laurussia from North/Central Europe in the east to eastern Canada in the west, with north-south trending graben systems developing across Europe, including further subsidence in the Northern and SouthernPermian basins.[14][16] Lower Triassic sediments deposited in these basins are continental to brackish marine in nature. They are overlain by shallow marinecarbonates andmudstones andevaporites of theZechstein Sea.[14]
Further south, during the Norian, the opening of the Central Atlantic led to the formation of narrow, deep water basins in the Eastern Mediterranean area.[14]Corsica,Sardinia,Calabria, and theBalearic terranes were attached to Europe, whilstApulia, Adria, and the terranes of southernTurkey remained attached to theAfrican plate.[16]
Along the western margin of Laurussia, a continentalmagmatic arc extended from the southwestern United States to the Arctic with an associated continental-scaleforeland basin system. Localisedback-arc basins developed within this, in regions of extension.[20] Along the northern section of the margin, the Permian to Early Triassic counterclockwise rotation of Pangea resulted in the closure of the narrowSlide Mountain Ocean and theSonoma orogeny.[14][21] In south, it led to a reduction in the dip of the subducting slab and thickening of thecontinental crust.[21]
Much of Africa was stable and above sea level, with only a few Triassic-aged lake sediments known, although along the northern coast marine sediments were deposited during periods of higher sea levels.[14]
Northeast-southwest trending rifting along the eastern edge of Africa betweenMadagascar (Indian plate) and eastern Africa (Somalian plate) continued from the Late Carboniferous into the Triassic, with substantial mountains rising along the edge of the rift and the formation of a series ofpull-apart basins. Gradual marine incursions from the Neo-Tethys resulted in the deposition of Lower and Middle Triassic marine sediments in these basins. Upper Triassic sediments are continental in nature and thisrift system ultimately failed and a new north-south trending rift system developed in the Jurassic.[14][22]
The opening of the Neo-Tethys createdpassive margins along the Arabian and Indian margins.[14][23] Rifting in the Neo-Tethys extended westwards between thePontides andTaurides terranes of Turkey during the Late Triassic.[14] The Tethyan Himalayan block remained attached to India but was separated by the thinned crust of Greater India, the northern margin of which supplied sediments to the passive margin.[24]
The counterclockwise rotation of Pangea precipitateddextraltranspression across the NNE-SSW trending, west-dipping subduction zone, along the eastern Australian margin, which culminated in theHunter-Bowen orogeny (c. 260-230 Ma).[17][25] Following this, the magmatic arc rotated to north-south and compression gave way to extension. This was accompanied bysubduction rollback and back-arc basin formation.[17][25]
Along the southwestern margin ofSouth America, low plate convergence and subduction rates, triggered by the assembly and rotation of Pangea, resulted in subduction rollback and extension across the back-arc region. This generated large amounts offelsicmagmatism.[26][17] These extensional forces stretched across the continent with the formation of large northwest-trending basins with thick sedimentary deposits and the extension related magmatism.[14]
The Paleo-Tethys ocean formed as the continents surrounding it assembled to form Pangea in the Late Palaeozoic.[27] The Eurasian sector of Pangea lay along its north and northwestern margin.[14] To the northeast, the narrow Paleoasian Ocean (a branch of the Paleo-Tethys) lay between Eurasia, and North China and Tarim, and to the east, South China and Annamia (Southeast Asia). To the south were the Cimmerian terranes (Central Iran,Qiangtang(north Tibet),Lhasa (south Tibet), andSibumasu (eastern Myanmar, Thailand, Malay peninsula and Sumatra). These terranes had rifted from northeastern Gondwana during the Permian. As they drifted northwards through the Triassic, the Paleo-Tethys closed in front of them, and the Neotethys opened behind.[14][15]
The Paleo-Tethys was being consumed by subduction zones along the southern margin of North China, much of the Eurasian margin, and along the northern margin of the Qiangtang-Annamia and Lhasa-Sibumasu blocks.[14][15]
Collisions between Annamia and South China (c. 246-230 Ma); between Sibumasu and South China–Annamia (c. 240-230 Ma); and, between Qiangtang and Lhasa (c. 250–230 Ma) resulted in the Indosinian orogeny and the formation of a single large Eastern Asian continent.[15] At about the same time (c. 240-230 Ma), the final closure of the Paleoasian Ocean led to the collision of Tarim and North China with the Kazakhstan and Siberian regions of Pangea, to form theCentral Asian orogenic belt.[15] South China collided with North China (c. 220 Ma), forming the Central China orogenic belt.[15] The segment of the Paleo-Tethys between North China and Qiangtang may never have fully closed, but was filled with Permo-Triassic turbidites preserved in the West Kunlun and Bayanhar belts of the Central China orogenic belt.[28]
The amalgamation of these East Asian blocks with Pangea in the Late Triassic maximised the land area of the supercontinent. It coincided with a period of dramatic climate change and the development of the megamonsoon, although the relationship between these is the subject of ongoing research.[15]
The western Paleo-Tethys remained open until about 205 Ma, when the Iranian blocks collided with the Turan platform, on the southern margin of Eurasia, resulting in the Cimmerian orogeny. This extended from theAnatolian Plateau in the northwest, and merged with the Indosinian orogenic belt in the east.[14][29] Late Triassic deformation across the Eastern Mediterranean area and much of the Middle East was complex, with regional scalestrike-slip faulting and continued subduction below the Iranian margin.[14]
Beginning in the latest Permian, a broad zone oflithospheric extension developed across Pangea along the line of the future Central Atlantic Ocean.[18][30] The location of this rifting followed the pre-existing structures of theVariscan orogeny, and began immediately after theorogenic collapse of the Variscan belt.[18][22] Extension began in the northern Central Atlantic region in the Anisian, and in the southern Central Atlantic in the Carnian.[18][30]
Major rift basins formed along the present-day eastern North American margin from Florida to Newfoundland (Newark Supergroup basins), and along the Europe/African margin (Moroccan and Iberian basins). The Moroccan basins are the equivalent of Nova Scotian basins, and the Iberian the equivalent of the Newfoundland basins.[30] These basins formed broad depressions on the continental crust that extended for hundreds of kilometres across central Pangea, with localised faulting formed sub-basins.[22] The basins were filled by mainly continental deposits from regional-scale river systems and lakes, with only minor, late marine incursions in some areas.[30][22]
The period of rifting came to an end with the emplacement of the Central Atlantic Magmatic Province (CAMP) around 201 Ma. This was followed by seafloor spreading and the opening of the Central Atlantic Ocean.[18] The CAMP is one of the largest LIPs and covered a region of about 10 million km2 across North America, northeastern South America, northwestern Africa, and southwestern Europe.[14][18] The magmatism produced densedyke swarms, with individual dykes up to 800 km long, massivesill complexes, andlava fields that covered several hundred kilometres.[31] Despite its size, the period of magmatism was brief, lasting only about 1 million years. Such intense igneous activity indicates widespreadmantle melting, rather than a simpleplume within the mantle. The variedpetrological composition of the CAMP magmatism reflects local contamination of the upper mantle by continental lithosphere, including partial melting of previously subducted slabs.[18][31] The magmatism, with its large scale injection of carbon and sulphur into the atmosphere, precipitatedvolcanic winters. This was followed by longer-term climate warming andocean acidification, which caused the end-Triassic mass extinction.[18][32][31]
Although no direct evidence remains, Panthalassa is thought to have been divided into three major tectonic plates: theFarallon;Izanagi; and,Phoenix. These were separated by oceanic spreading ridges. In the northeast, the smaller Cache Creek plate was being subducted beneath the western margin of North America, and beneath the Farallon plate to the south.[14]
Eustatic sea level in the Triassic was consistently low compared to the other geological periods. The beginning of the Triassic was around present sea level, rising to about 10–20 metres (33–66 ft) above present-day sea level during the Early and Middle Triassic. Sea level rise accelerated in the Ladinian, culminating with a sea level up to 50 metres (164 ft) above present-day levels during the Carnian. Sea level began to decline in the Norian, reaching a low of 50 metres (164 ft) below present sea level during the mid-Rhaetian. Low global sea levels persisted into the earliest Jurassic. The long-term sea level trend is superimposed by 22 sea level drop events widespread in the geologic record, mostly of minor (less than 25-metre (82 ft)) and medium (25–75-metre (82–246 ft)) magnitudes. A lack of evidence for Triassic continental ice sheets suggest that glacial eustasy is unlikely to be the cause of these changes.[34] It has generally been assumed that the cause was changes in volume of the global ocean basin due to variations in oceanic volcanism, with largest volumes occurring in volcanism's absence when the ocean basins were subsiding.[35] Variation in water and sediment delivery to the oceans, with higher sea levels during pluvial eras lasting up to four million years, is also hypothesised to be behind these sea level variations.[34]
The Triassic continental interior climate was generally hot and dry, so that typical deposits arered bedsandstones andevaporites. There is no evidence ofglaciation at or near either pole; in fact, the polar regions were apparently moist andtemperate, providing a climate suitable for forests and vertebrates, including reptiles. Pangaea's large size limited the moderating effect of the global ocean; itscontinental climate was highly seasonal, with very hot summers and cool winters.[36] The strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorialmonsoons,[36] sometimes referred to as thePangean megamonsoons.[37]
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.[38] 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), theNorth American continent, the SouthChina block andArgentina. The best-studied of such episodes of humid climate, and probably the most intense and widespread, was theCarnian Pluvial Event.
The Early Triassic was the hottest portion of the entire Phanerozoic, seeing as it occurred during and immediately after the discharge of titanic volumes ofgreenhouse gases from the Siberian Traps. The Early Triassic began with thePermian-Triassic Thermal Maximum (PTTM) and was followed by the briefDienerian Cooling (DC) from 251 to 249 Ma, which was in turn followed by the LatestSmithian Thermal Maximum (LSTT) around 249 to 248 Ma. During the LatestOlenekian Cooling (LOC), from 248 to 247 Ma, temperatures cooled by about 6 °C.[39]
The Middle Triassic was cooler than the Early Triassic, with temperatures falling over most of the Anisian, with the exception of a warming spike in the latter portion of the stage.[40] From 242 to 233 Ma, the Ladinian-Carnian Cooling (LCC) ensued.[39]
At the beginning of the Carnian, global temperatures continued to be relatively cool.[41] The eruption of the Wrangellia Large Igneous Province around 234 Ma caused abrupt global warming, terminating the cooling trend of the LCC.[42] This warming was responsible for the Carnian Pluvial Event and resulted in an episode of widespread global humidity.[43] The CPE ushered in the Mid-Carnian Warm Interval (MCWI), which lasted from 234 to 227 Ma.[39] At the Carnian-Norian boundary occurred a positiveδ13C excursion believed to signify an increase in organic carbon burial.[44] From 227 to 217 Ma, there was a relatively cool period known as the Early Norian Cool Interval (ENCI), after which occurred the Mid-Norian Warm Interval (MNWI) from 217 to 209 Ma. The MNWI was briefly interrupted around 214 Ma by a cooling possibly related to theManicouagan impact.[39] Around 212 Ma, a 10 Myr eccentricity maximum caused a paludification of Pangaea and a reduction in the size of arid climatic zones.[45] The Rhaetian Cool Interval (RCI) lasted from 209 to 201 Ma.[39] At the terminus of the Triassic, there was an extreme warming event referred to as the End-Triassic Thermal Event (ETTE), which was responsible for the Triassic-Jurassic mass extinction.[39] Bubbles ofcarbon dioxide in basaltic rocks dating back to the end of the Triassic indicate that volcanic activity from the Central Atlantic Magmatic Province helped trigger climate change in the ETTE.[46]
During the Early Triassic,lycophytes, particularly those of the orderIsoetales (which contains livingquillworts), rose to prominence due to the environmental instability following the Permian-Triassic extinction, with one particularly notable example being the genusPleuromeia, which grew in columnar like fashion, sometimes reaching a height of 2 metres (6.6 ft). The relevance of lycophytes declined from the Middle Triassic onwards, following the return of more stable environmental conditions.[47]
While having first appeared during the Permian, the extinct seed plant groupBennettitales first became a prominent element in global floras during the Late Triassic, a position they would hold for much of the Mesozoic.[48] In the Southern Hemisphere landmasses of Gondwana, the treeDicroidium, an extinct "seed fern" belong to the orderCorystospermales was a dominant element in forest habitats across the region during the Middle-Late Triassic.[49] During the Late Triassic, theGinkgoales (which today are represented by only a single species,Ginkgo biloba) underwent considerable diversification.[50] Conifers were abundant during the Triassic, and included theVoltziales (which contains various lineages, probably including those ancestral to modern conifers),[51] as well as the extinct familyCheirolepidiaceae, which first appeared in the Late Triassic, and would be prominent throughout most of the rest of the Mesozoic.[52]
Immediately above the Permian–Triassic boundary theglossopteris flora was suddenly[53] largely displaced by anAustralia-wide coniferous flora.
No knowncoal deposits date from the start of the Triassic Period. This is known as theEarly Triassic "coal gap" and can be seen as part of thePermian–Triassic extinction event.[54] Possible explanations for the coal gap include sharp drops in sea level at the time of the Permo-Triassic boundary;[55] acid rain from the Siberian Traps eruptions or from an impact event that overwhelmed acidic swamps; climate shift to a greenhouse climate that was too hot and dry for peat accumulation; evolution of fungi or herbivores that were more destructive of wetlands; the extinction of all plants adapted to peat swamps, with a hiatus of several million years before new plant species evolved that were adapted to peat swamps;[54] or soil anoxia as oxygen levels plummeted.[56]
Before the Permian extinction,Archaeplastida (red and green algae) had been the major marinephytoplanktons since about 659–645 million years ago,[57] when they replaced marine planktoniccyanobacteria, which first appeared about 800 million years ago, as the dominant phytoplankton in the oceans.[58] In the Triassic,secondary endosymbiotic algae became the most important plankton.[59]
Inmarine environments, new modern types ofcorals appeared in the Early Triassic, forming small patches ofreefs of modest extent compared to the great reef systems ofDevonian or modern times. At the end of the Carnian, a reef crisis occurred in South China.[60]Serpulids appeared in the Middle Triassic.[61]Microconchids were abundant. The shelledcephalopods calledammonites recovered, diversifying from a single line that survived the Permian extinction. Bivalves began to rapidly diversify during the Middle Triassic, becoming highly abundant in the oceans.[62]
Aquatic insects rapidly diversified during the Middle Triassic, with this time interval representing a crucial diversification forHolometabola, the clade containing the majority of modern insect species.[63]
In the wake of thePermian-Triassic mass extinction event, thefish fauna was remarkably uniform, with manyfamilies andgenera exhibiting acosmopolitan distribution.[64]Coelacanths show their highest post-Devonian diversity in theEarly Triassic.[65]Ray-finned fishes (actinopterygians) went through a remarkable diversification in the beginning of the Triassic, leading to peak diversity during the Middle Triassic; however, the pattern of this diversification is still not well understood due to ataphonomic megabias.[66] The firststem-groupteleosts appeared during the Triassic (teleosts are by far the most diverse group of fish today).[64] Predatory actinopterygians such assaurichthyids andbirgeriids, some of which grew over 1.2 m (3.9 ft) in length, appeared in the Early Triassic and became widespread and successful during the period as a whole.[67] Lakes and rivers were populated bylungfish (Dipnoi), such asCeratodus, which are mainly known from the dental plates, abundant in the fossils record.[68]Hybodonts, a group of shark-likecartilaginous fish, were dominant in both freshwater and marine environments throughout the Triassic.[69] Last survivors of the mainlyPalaeozoicEugeneodontida are known from the Early Triassic.[70]
Temnospondylamphibians were among those groups that survived the Permian–Triassic extinction. Once abundant in both terrestrial and aquatic environments, the terrestrial species had mostly died out during the extinction event. The Triassic survivors were aquatic or semi-aquatic, and were represented byTupilakosaurus,Thabanchuia,Branchiosauridae andMicropholis, all of which died out in Early Triassic, and the successfulStereospondyli, with survivors into the Cretaceous Period. The largest Triassic stereospondyls, such asMastodonsaurus, were up to 4 to 6 metres (13 to 20 ft) in length.[71][72] 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.Plagiosaurus,metoposaurs).
The firstLissamphibians (modern amphibians) appear in the Triassic, with the progenitors of the firstfrogs already present by the Early Triassic. However, the group as a whole did not become common until theJurassic, when the temnospondyls had become very rare.
Most of theReptiliomorpha, stem-amniotes that gave rise to the amniotes, disappeared in the Triassic, but two water-dwelling groups survived:Embolomeri that only survived into the early part of the period, and theChroniosuchia, which survived until the end of the Triassic.
The Permian–Triassic extinction devastated terrestrial life. Biodiversity rebounded as thesurviving species repopulated empty terrain, but these were short-lived. Diverse communities with complexfood-web structures took 30 million years to reestablish.[10][73]Archosauromorph reptiles, which had already appeared and diversified to an extent in the Permian Period, exploded in diversity as anadaptive radiation in response to the Permian-Triassic mass extinction. By the Early Triassic, several major archosauromorph groups had appeared. Long-necked, lizard-like early archosauromorphs were known asprotorosaurs, which is likely a paraphyletic group rather than a true clade.Tanystropheids were a family of protorosaurs which elevated their neck size to extremes, with the largest genusTanystropheus having a neck longer than its body. The protorosaur familySharovipterygidae used their elongated hindlimbs for gliding. Other archosauromorphs, such asrhynchosaurs andallokotosaurs, were mostly stocky-bodied herbivores with specialized jaw structures.
Rhynchosaurs, barrel-gutted herbivores, thrived for only a short period of time, becoming extinct about 220 million years ago. They were exceptionally abundant in the middle of the Triassic, as the primary large herbivores in many Carnian-age ecosystems. They sheared plants with premaxillary beaks and plates along the upper jaw with multiple rows of teeth. Allokotosaurs were iguana-like reptiles, includingTrilophosaurus (a common Late Triassic reptile with three-crowned teeth),Teraterpeton (which had a long beak-like snout), andShringasaurus (a horned herbivore which reached a body length of 3–4 metres (9.8–13.1 ft)).
One group of archosauromorphs, thearchosauriforms, were distinguished by their active predatory lifestyle, with serrated teeth and upright limb postures. Archosauriforms were diverse in the Triassic, including various terrestrial and semiaquatic predators of all shapes and sizes. The large-headed and robusterythrosuchids were among the dominant carnivores in the early Triassic.Phytosaurs were a particularly common group which prospered during the Late Triassic. These long-snouted and semiaquatic predators resemble living crocodiles and probably had a similar lifestyle, hunting for fish and small reptiles around the water's edge. However, this resemblance is only superficial and is a prime-case of convergent evolution.
Truearchosaurs appeared in the early Triassic, splitting into two branches:Avemetatarsalia (the ancestors to birds) andPseudosuchia (the ancestors to crocodilians). Avemetatarsalians were a minor component of their ecosystems, but eventually produced the earliestpterosaurs anddinosaurs in the Late Triassic. Early long-tailed pterosaurs appeared in the Norian and quickly spread worldwide. Triassic dinosaurs evolved in the Carnian and include early sauropodomorphs and theropods. Most Triassic dinosaurs were small predators and only a few were common, such asCoelophysis, which was 1 to 2 metres (3.3 to 6.6 ft) long. Triassicsauropodomorphs primarily inhabited cooler regions of the world.[74]
The large predatorSmok was most likely also an archosaur, but it is uncertain if it was a primitive dinosaur or a pseudosuchian.
Pseudosuchians were far more ecologically dominant in the Triassic, including large herbivores (such asaetosaurs), large carnivores ("rauisuchians"), and the firstcrocodylomorphs ("sphenosuchians").Aetosaurs were heavily-armored reptiles that were common during the last 30 million years of the Late Triassic until they died out at the Triassic-Jurassic extinction. Most aetosaurs were herbivorous and fed on low-growing plants, but some may have eaten meat. "rauisuchians" (formally known asparacrocodylomorphs) were the keystone predators of most Triassic terrestrial ecosystems. Over 25 species have been found, including giant quadrupedal hunters, sleek bipedal omnivores, and lumbering beasts with deep sails on their backs. They probably occupied the large-predator niche later filled by theropods. "Rauisuchians" were ancestral to small, lightly-built crocodylomorphs, the only pseudosuchians which survived into the Jurassic.
Among other reptiles, the earliestturtles, likeProganochelys andProterochersis, appeared during theNorian Age (Stage) of the Late Triassic Period. TheLepidosauromorpha, specifically theSphenodontia, are first found in the fossil record of the earlier Carnian Age, though the earliest lepidosauromorphs likely occurred in the Permian. TheProcolophonidae, the last survivingparareptiles, were an important group of small lizard-like herbivores. Thedrepanosaurs were a clade of unusual, chameleon-like arboreal reptiles with birdlike heads and specialised claws.
During the Triassic, archosaurs displaced therapsids as the largest and most ecologically prolific terrestrial amniotes. This "Triassic Takeover" may have contributed to theevolution of mammals by forcing the surviving therapsids and theirmammaliaform successors to live as small, mainly nocturnalinsectivores.Nocturnal life may have forced the mammaliaforms to develop fur and a highermetabolic rate.[77]
Lystrosaurus was a widespread dicynodont and the most common land vertebrate during the Early Triassic, after animal life had been greatly diminished
The Triassic Period ended with a mass extinction, which was particularly severe in the oceans; theconodonts disappeared, as did all the marine reptiles exceptichthyosaurs andplesiosaurs. Invertebrates likebrachiopods andmolluscs (such asgastropods) 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 ofcrurotarsans (large archosaurian reptiles previously grouped together as thethecodonts) disappeared, as did most of the large labyrinthodont amphibians, groups of small reptiles, and most synapsids. 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 hugevolcanic eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago (40Ar/39Ar dates),[80] forming theCentral Atlantic Magmatic Province (CAMP),[81] 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 abolide impact, for which an impact crater containingManicouagan Reservoir inQuebec,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 201.4 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.[82]
Skull of a Triassic Period phytosaur found in the Petrified Forest National Park
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 thePetrified 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.[83]Phytosaurs, the most common fossils there, experienced a change-over only at the genus level, and the number of species remained the same. Someaetosaurs, 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 herbivoroustherapsids—thekannemeyeriid dicynodonts and thetraversodont 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.
^Friedrich von Alberti,Beitrag zu einer Monographie des bunten Sandsteins, Muschelkalks und Keupers, und die Verbindung dieser Gebilde zu einer Formation [Contribution to a monograph on the colored sandstone, shell limestone and mudstone, and the joining of these structures into one formation] (Stuttgart and Tübingen, (Germany): J. G. Cotta, 1834). Alberti coined the term "Trias" onpage 324 : "… bunter Sandstein, Muschelkalk und Keuper das Resultat einer Periode, ihre Versteinerungen, um mich der Worte E. de Beaumont's zu bedeinen, die Thermometer einer geologischen Epoche seyen, … also die bis jezt beobachtete Trennung dieser Gebilde in 3 Formationen nicht angemessen, und es mehr dem Begriffe Formation entsprechend sey, sie zu einer Formation, welche ich vorläufigTrias nennen will, zu verbinden." ( … colored sandstone, shell limestone, and mudstone are the result of a period; their fossils are, to avail myself of the words of E. de Beaumont, the thermometer of a geologic epoch; … thus the separation of these structures into 3 formations, which has been maintained until now, isn't appropriate, and it is more consistent with the concept of "formation" to join them into one formation, which for now I will name "trias".)
^abcdefghijklmnopqrstuTorsvik, Trond H.; Cocks, Leonard Robert Morrison (2017).Earth history and palaeogeography. Cambridge: Cambridge university press.ISBN978-1-107-10532-4.
^abcMarzoli, Andrea; Callegaro, Sara; Dal Corso, Jacopo; Davies, Joshua H. F. L.; Chiaradia, Massimo; Youbi, Nassrrdine; Bertrand, Hervé; Reisberg, Laurie; Merle, Renaud (2018)."The Central Atlantic Magmatic Province (CAMP): A Review". In Tanner, Lawrence H. (ed.).The Late Triassic World: Earth in a Time of Transition. Cham: Springer International Publishing. pp. 91–125.doi:10.1007/978-3-319-68009-5_4.ISBN978-3-319-68009-5. Retrieved2025-06-25.
^Embry, Ashton F. (1985). "Triassic Sea-Level Changes: Evidence from the Canadian Arctic Archipelago". In Wilgus, Cheryl K.; Hastings, Bruce S.; Posamentier, Henry; van Wagoner, John; Ross, Charles A.; Kendall, Christopher G. St. C. (eds.).Sea-Level Changes: An Integrated Approach.Calgary,Alberta: Geological Survey of Canada. pp. 249–259.
^Preto, N.; Kustatscher, E.; Wignall, P. B. (2010). "Triassic climates – State of the art and perspectives".Palaeogeography, Palaeoclimatology, Palaeoecology.290 (1–4):1–10.Bibcode:2010PPP...290....1P.doi:10.1016/j.palaeo.2010.03.015.
^Agnolin, F. L., Mateus O., Milàn J., Marzola M., Wings O., Adolfssen J. S., & Clemmensen L. B. (2018). Ceratodus tunuensis, sp. nov., a new lungfish (Sarcopterygii, Dipnoi) from the Upper Triassic of central East Greenland. Journal of Vertebrate PaleontologyJournal of Vertebrate Paleontology. e1439834
^Kumar, Krishna; Bajpai, Sunil; Pandey, Pragya; Ghosh, Triparna; Bhattacharya, Debasish (2021-08-04). "Hybodont sharks from the Jurassic of Jaisalmer, western India".Historical Biology.34 (6):953–963.doi:10.1080/08912963.2021.1954920.ISSN0891-2963.S2CID238781606.
^Mutter, Raoul J.; Neuman, Andrew G. (2008). "New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada". In Cavin, L.; Longbottom, A.; Richter, M. (eds.).Fishes and the Break-up of Pangaea. Geological Society of London, Special Publications. Vol. 295. London: Geological Society of London. pp. 9–41.doi:10.1144/sp295.3.S2CID130268582.
Emiliani, Cesare. (1992).Planet Earth: Cosmology, Geology, & the Evolution of Life & the Environment. Cambridge University Press. (Paperback EditionISBN0-521-40949-7)
Ogg, Jim; June, 2004,Overview of Global Boundary Stratotype Sections and Points (GSSP's)Stratigraphy.org, Accessed April 30, 2006
Stanley, Steven M.Earth System History. New York: W.H. Freeman and Company, 1999.ISBN0-7167-2882-6
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