Triassic ( /traɪˈæsɪk/) is a geologic period and system which
spans 50.9 million years from the end of the
Permian Period 251.9
million years ago (Mya), to the beginning of the
Jurassic Period 201.3
Triassic is the first period of the
Mesozoic Era. Both the
start and end of the period are marked by major extinction events.
Triassic began in the wake of the Permian–
event, which left the earth's biosphere impoverished; it would take
well into the middle of this period for life to recover 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
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
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
Jurassic extinction event, that wiped out many groups and
allowed dinosaurs to assume dominance in the Jurassic.
Triassic was named in 1834 by Friedrich von Alberti, after the
three distinct rock layers (tri meaning "three") that are found
Germany and northwestern Europe—red beds, capped by
marine limestone, followed by a series of terrestrial mud- and
sandstones—called the "Trias".
1 Dating and subdivisions
2.3 South America
4.2 Marine fauna
4.3 Terrestrial and freshwater fauna
Jurassic extinction event
8 See also
11 External links
Dating and subdivisions
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
Late Triassic (Tr3)
(208.5 – 201.3 Mya)
(227 – 208.5 Mya)
(237– 227 Mya)
Middle Triassic (Tr2)
(242 – 237 Mya)
(247.2 – 242 Mya)
Early Triassic (Scythian)
(251.2 – 247.2 Mya)
(251.902– 251.2 Mya)
230 Ma plate tectonic reconstruction
Australia lies on
Triassic shales and sandstones. Almost all
of the exposed rocks around
Sydney belong to the
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
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
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.
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
Because a super-continental mass has less shoreline compared to one
Triassic marine deposits are globally relatively rare,
despite their prominence in Western Europe, where the
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
Late Triassic fossils are found throughout Africa, but are
more common in the south than north. The time boundary separating
Triassic marks the advent of an extinction event with
global impact, although African strata from this time period have not
been thoroughly studied.
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
Brasilodon have been
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
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
Ladinian of the Tethysian
domain, and from the
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.
Triassic flora as depicted in
Meyers Konversations-Lexikon (1885–90)
Three categories of organisms can be distinguished in the Triassic
record: holdovers from the Permian-
Triassic extinction, new groups
which flourished briefly, and other new groups which went on to
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
Glossopteris (a seed fern) was the dominant southern
hemisphere tree during the
Early Triassic period.
Marine vertebrate apex predators of the early Triassic
Middle Triassic marginal marine sequence, southwestern Utah
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.
abundant. The shelled cephalopods called ammonites recovered,
diversifying from a single line that survived the
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
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.
Terrestrial and freshwater fauna
Groups of terrestrial fauna, which appeared in the
Triassic period or
achieved a new level of evolutionary success during it
Temnospondyls: one of the largest groups of early amphibians,
temnospondyls originated during the
Carboniferous and were still
significant. Once abundant in both terrestrial and aquatic
environments, the terrestrial species had mostly been replaced by
Triassic survivors were aquatic or semi-aquatic, and
were represented by Tupilakosaurus, Thabanchuia,
Micropholis, all of which died out in early Triassic, and the
successful Stereospondyli, with survivors into the
Cretaceous era. The
largest of these, such as the
Mastodonsaurus were up to 13 ft in
Rhynchosaurs, barrel-gutted herbivores which thrived for only a short
period of time, becoming extinct about 220 million years ago. They
were exceptionally abundant in Triassic, the primary large herbivores
in many ecosystems. They sheared plants with their beaks and several
rows of teeth on the roof of the mouth.
Phytosaurs: archosaurs that 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.
Aetosaurs: heavily armored archosaurs that were common during the last
30 million years of the late
Triassic but died out at the
Jurassic extinction. Most aetosaurs were herbivorous, and fed
on low-growing plants but some may have eaten meat.
Rauisuchians, another group of archosaurs, which were the keystone
predators of most
Triassic terrestrial ecosystems. Over 25 species
have been found, and include 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.
Theropods: dinosaurs that first evolved in the
Triassic period but did
not evolve into large sizes until the Jurassic. Most Triassic
theropods, such as the Coelophysis, were only around 1–2 meters long
and hunted small prey in the shadow of the giant Rauisuchians.
Cynodonts, a large group that includes true mammals. The first
cynodonts evolved in the Permian, but many groups prospered during the
Triassic. Their characteristic mammalian features included hair, a
large brain, and upright posture. Many were small but several forms
were enormous and filled a large herbivore niche before the evolution
of sauropodomorph dinosaurs, as well as large sized carnivorous
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
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
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
Embolomeri that only survived into the early part of the
period, and the Chroniosuchia, which survived until the end of
Archosauromorph reptiles, especially archosaurs, progressively
replaced the synapsids that had dominated the previous
Cynognathus was the characteristic top predator in earlier
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
Prolacertiformes were important basal archosauromorph
groups throughout most of the Triassic.
Among other reptiles, the earliest turtles, like
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
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.
Postosuchus An apex predator of its time which preyed on anything
smaller than itself.
Staurikosaurus feeding on a dicynodont, in geopark Paleorrota.
Lystrosaurus was the most common land vertebrate during the Early
Triassic, when animal life had been greatly diminished.
Reconstruction of Proterosuchus, a genus of crocodile-like carnivorous
reptile that existed in the Early Triassic.
Cynognathus was a mammal-like cynodont from the early Triassic. The
first true mammals evolved during this period.
Plateosaurus was an early sauropodomorph, or "prosauropod", of the
Coelophysis, one of the first dinosaurs, appeared in the Late
Life reconstruction of
No known coal deposits date from the start of the
This is known as the "coal gap" and can be seen as part of the
Triassic extinction event. Sharp drops in sea level at
the time of the Permo
Triassic boundary may be the best explanation
for the coal gap. However, there is still speculation as to why it is
missing. During the preceding
Permian period the arid desert
conditions contributed to the evaporation of many inland seas and the
subsequent inundation of those area, perhaps by a number of tsunami
events that may have been responsible for the drop in sea level.
Large salt basins in the southwest United States and a very large
basin in central
Canada are evidence of this. Coal of
is made of the fossilized remains of
Triassic plants and trees.
Immediately above the Permian-
Triassic boundary the glossopteris flora
was suddenly largely displaced by an Australia-wide coniferous
flora containing few species with a lycopod herbaceous under story.
Conifers also became common in Eurasia. These groups of conifers arose
from endemic species because of the ocean barriers that prevented seed
from crossing for over one hundred million years. For instance,
Podocarpis was located south and pines, junipers, and sequoias were
located north. The dividing line ran through the Amazon Valley, across
the Sahara, and north of Arabia, India, Thailand, and
Australia. It has been suggested that there was a climate
barrier for the conifers. although water barriers are more
plausible. If so, something that could cross at least minor water
barriers must have been involved in producing the coal hiatus. Hot
climate could have been an important auxiliary factor across
Antarctica or the Bering Strait, however. There was a spike of fern
and lycopod spores immediately after the close of the Permian.
There was also a spike of fungal spores immediately after the
Triassic boundary. This spike may have lasted 50,000 years
Italy and 200,000 years in
China and must have contributed to the
An event excluding a catastrophe must have been involved to cause the
coal hiatus because fungi would have removed all dead vegetation and
coal forming detritus in a few decades in most tropical places. In
addition, fungal spores rose gradually and declined similarly along
with a prevalence of woody debris. Each phenomenon would hint at
widespread vegetative death. Whatever the cause of the coal hiatus, it
must have started in
North America approximately 25 million years
Triassic sandstone near Stadtroda, Germany
Monte San Giorgio lagerstätte, now in the
Lake Lugano region of
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
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).
Jurassic extinction event
Main article: Triassic–
Jurassic extinction event
The mass extinction event is marked by 'End Tr'
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
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
Pangaea began to break apart about 202 to 191 million
years ago (40Ar/39Ar dates), 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 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, therefore, not be the
immediate cause of the observed mass extinction.
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
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
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
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
rather than the Triassic.
Geologic time scale
List of fossil sites
List of fossil sites (with link directory)
Phanerozoic Carbon Dioxide.png
^ Image:All palaeotemps.png
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( … colored sandstone, shell limestone, and mudstone are the result
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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".)
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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. ISBN 0-7167-2882-6
Sues, Hans-Dieter & Fraser, Nicholas C.
Triassic Life on Land: The
Great Transition New York: Columbia University Press, 2010. Series:
Critical Moments and Perspectives in Earth History and Paleobiology.
van Andel, Tjeerd, (1985) 1994, New Views on an Old Planet: A History
of Global Change, Cambridge University Press
Wikimedia Commons has media related to Triassic.
Look up triassic in Wiktionary, the free dictionary.
A Visit To
Ammonite Canyon, Nevada Virtual field trip to one of the
most famous places on Earth to study the
Late Triassic extinction in a
marine geologic section.
Middle Triassic Ammonoids From Nevada
Ammonoids At Union Wash, California Virtual field trip to a classic
Triassic ammonoid locality in Inyo County, California.
Ichthyosaur And Invertebrate Fossils In Nevada
Early Triassic Ammonoid Fossils In Nevada
Douglas Henderson's illustrations of
Triassic animals[permanent dead
Paleofiles page on the
Geologic history of Earth
Quaternary (present–2.588 Mya)
Holocene (present–11.784 kya)
Pleistocene (11.784 kya–2.588 Mya)
Neogene (2.588–23.03 Mya)
Pliocene (2.588–5.333 Mya)
Miocene (5.333–23.03 Mya)
Paleogene (23.03–66.0 Mya)
Oligocene (23.03–33.9 Mya)
Eocene (33.9–56.0 Mya)
Paleocene (56.0–66.0 Mya)
Cretaceous (66.0–145.0 Mya)
Late (66.0–100.5 Mya)
Early (100.5–145.0 Mya)
Jurassic (145.0–201.3 Mya)
Late (145.0–163.5 Mya)
Middle (163.5–174.1 Mya)
Early (174.1–201.3 Mya)
Triassic (201.3–251.902 Mya)
Late (201.3–237 Mya)
Middle (237–247.2 Mya)
Early (247.2–251.902 Mya)
Permian (251.902–298.9 Mya)
Lopingian (251.902–259.8 Mya)
Guadalupian (259.8–272.3 Mya)
Cisuralian (272.3–298.9 Mya)
Carboniferous (298.9–358.9 Mya)
Pennsylvanian (298.9–323.2 Mya)
Mississippian (323.2–358.9 Mya)
Devonian (358.9–419.2 Mya)
Late (358.9–382.7 Mya)
Middle (382.7–393.3 Mya)
Early (393.3–419.2 Mya)
Silurian (419.2–443.8 Mya)
Pridoli (419.2–423.0 Mya)
Ludlow (423.0–427.4 Mya)
Wenlock (427.4–433.4 Mya)
Llandovery (433.4–443.8 Mya)
Ordovician (443.8–485.4 Mya)
Late (443.8–458.4 Mya)
Middle (458.4–470.0 Mya)
Early (470.0–485.4 Mya)
Cambrian (485.4–541.0 Mya)
Furongian (485.4–497 Mya)
Series 3 (497–509 Mya)
Series 2 (509–521 Mya)
Terreneuvian (521–541.0 Mya)
(541.0 Mya–2.5 Gya)
Neoproterozoic era (541.0 Mya–1 Gya)
Ediacaran (541.0-~635 Mya)
Cryogenian (~635-~720 Mya)
Tonian (~720 Mya-1 Gya)
Mesoproterozoic era (1–1.6 Gya)
Stenian (1-1.2 Gya)
Ectasian (1.2-1.4 Gya)
Calymmian (1.4-1.6 Gya)
Paleoproterozoic era (1.6–2.5 Gya)
Statherian (1.6-1.8 Gya)
Orosirian (1.8-2.05 Gya)
Rhyacian (2.05-2.3 Gya)
Siderian (2.3-2.5 Gya)
Archean eon² (2.5–4 Gya)
Neoarchean (2.5–2.8 Gya)
Mesoarchean (2.8–3.2 Gya)
Paleoarchean (3.2–3.6 Gya)
Eoarchean (3.6–4 Gya)
Hadean eon² (4–4.6 Gya)
kya = thousands years ago. Mya = millions years ago.
Gya = billions
years ago.¹ =
Phanerozoic eon. ² =
Source: (2017/02). International Commission on Stratigraphy. Retrieved
13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic
and Geochronologic Units USGS Retrieved 10 March 2013.