is a geologic period and system
that extends from
about 251 to 199 Ma
(million years ago). As
the first period of the Mesozoic
Triassic follows the Permian
and is followed
by the Jurassic
. Both the start and end of
the Triassic are marked by major extinction events
. The extinction event
that closed the Triassic period has recently been more accurately
dated, but as with most older geologic periods, the rock beds that
define the start and end are well identified, but the exact dates
of the start and end of the period are uncertain by a few million
During the Triassic, both marine and continental life show an
the starkly impoverished biosphere
followed the Permian-Triassic
. Corals of the hexacorallia
group made their first appearance.
The first flying vertebrates, the pterosaurs
, evolved during the Triassic.
Dating and subdivisions
Triassic was named in 1834 by Friedrich Von Alberti from the three
distinct layers (Latin trias meaning triad)—red beds,
capped by chalk, followed by black shales—that are found throughout Germany and
northwest Europe, called the
The Triassic is usually separated into Early
and Late Triassic Epoch
, and the corresponding rocks are
referred to as Lower, Middle, or Upper Triassic. The faunal stages
from the youngest to oldest
230 Ma plate tectonic
During the Triassic, almost all the Earth's land mass was
concentrated into a single supercontinent
centered more or less on the
equator, called Pangaea
("all the land").
From the east a vast gulf entered Pangaea, the Tethys sea
. It opened farther westward in the
mid-Triassic, at the expense of the shrinking Paleo-Tethys Ocean
, an ocean that existed
during the Paleozoic
. 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
of oceanic plates; thus, very
little is known of the Triassic open ocean.The supercontinent
Pangaea was rifting during the Triassic—especially late in the
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 of the
limited shoreline of one super-continental mass, Triassic marine
deposits are globally relatively rare, despite their prominence in
, 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
mostly based on organisms living 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 through-out
Africa, but are more common in the south than north. The boundary
separating the Triassic and Jurassic marks the advent of an
extinction event with global impact, although African strata from
this time period have not been thoroughly studied.
The Triassic climate was generally hot and dry, forming typical
red bed sandstones
. There is no evidence of
at or near either pole; in fact,
the polar regions were apparently moist and temperate
, a climate suitable for reptile-like
creatures. Pangaea's large size limited the moderating effect of
the global ocean; its continental
was highly seasonal, with very hot summers and cold
winters. It probably had strong, cross
Three categories of organisms can be distinguished in the Triassic
record: holdovers from the Permian-Triassic extinction
groups which flourished briefly, and other new groups which went on
to dominate the Mesozoic
On land, the holdover plants included the lycophytes
, the dominant cycads
(represented in modern times by Ginkgo
) and glossopterid
, or seed plants
came to dominate the terrestrial flora: in the northern hemisphere,
) was the dominant southern hemisphere tree during the
Early Triassic period.
In marine environments
, new modern types of
appeared in the Early Triassic,
forming small patches of reefs
extent compared to the great reef systems of Devonian
times or modern reefs. The shelled
recovered, diversifying from a single
line that survived the Permian extinction. The fish fauna was
remarkably uniform, reflecting the fact that very few families
survived the Permian extinction. There were also many types of
marine reptiles. These included the Sauropterygia
, which featured pachypleurosaurs
(both common during the Middle
Triassic, especially in the Tethys
, and the first
; the first of the lizardlike
); and the highly successful
, which appeared in Early
Triassic seas and soon diversified, some eventually developing to
huge size during the late Triassic.
The Permian-Triassic extinction devastated terrestrial life.
Biodiversity rebounded with the influx of disaster taxa, however
these were short lived. Diverse communities with complex trophic
structures took 30 million years to reestablish.
were among those groups that survived
the Permian-Triassic extinction, some lineages (e.g. Trematosaurs)
flourishing 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,
). As for other amphibians,
the first Lissamphibia
by the first frogs
, are known from the Early
Triassic, but the group as a whole did not become common until the
, when the temnospondyls had become
replaced the synapsids
that had dominated
the Permian. Although Cynognathus
was a characteristic top
predator in earlier Triassic (Olenekian
, and both kannemeyeriid dicynodonts
and gomphodont cynodonts
remained important herbivores
during much of the period. By the end
of the Triassic, synapsids played only bit parts. During the
(early part of the Late Triassic),
some advanced cynodont 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
during the Late Triassic these also reached the height of their
diversity, with various groups including the phytosaurs
several distinct lineages of Rauisuchia
and the first crocodylians
). Meanwhile the stocky herbivorous
and the small to
medium-sized insectivorous or piscivorous Prolacertiformes
were important basal
throughout most of the Triassic.
Among other reptiles, the earliest turtles
, like Proganochelys
appeared during the Norian
(middle of the
Late Triassic). The Lepidosauromorpha
—are first known in the
fossil record a little earlier (during the Carnian). The Procolophonidae
were an important group of
small lizard-like herbivores.
Archosaurs were initially rarer than the therapsids
which had dominated Permian
terrestrial ecosystems, but they began to
displace therapsids in the mid-Triassic. This "Triassic Takeover"
may have contributed to the evolution of mammals
by forcing the
surviving therapsids and their mammaliform
successors to live as small,
mainly nocturnal insectivores
life probably forced at least the mammaliforms to develop fur and
higher metabolic rates
At the start of the Triassic period coal is noticeable by its
absence throughout the world. This is known as the "coal gap" and
can be seen as part of the Permian–Triassic
. Sharp drops in sea level across the Permo
Triassic boundary may be partially to blame. During the preceding
period the hot desert conditions had
contributed to the evaporation of many inland seas and the
inundation of these seas, perhaps by a number of tsunami events may
have been responsible for the drop in sea level. There are large
salt basins in the southwest United States and a very large basin
is suspected in central Canada.
Immediately above the boundary the glossopteris
flora was suddenly largely
displaced by an Australia wide coniferous flora containing few
species and containing a lycopod herbaceous under story. Conifers
became common in Eurasia also. Each of these groups of conifers
arose from endemic species because conifers are very poor at
crossing ocean barriers and they remained separated for hundreds of
millions of years, largely to the present. Podocarpis was south and
Pines, Junipers, and Sequoias were north, for instance. 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
can cross at least short 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 Straights,
however. There was a spike of fern and lycopod spores immediately
after the close of the Permian. In addition there was also a spike
of fungal spores immediately after the Permian-Triassic boundary.
This spike may have lasted 50,000 years in Italy and 200,000 years
in China and must have contributed to the climate warmth.
If so, something besides an instant catastrophe must have been
involved to cause the coal hiatus because fungi would surely have
removed all dead vegetation and coal forming detritus in a few
decades in most tropical places. Besides, the fungal spores rose
gradually and declined similarly. There was also much woody debris.
Each phenomenon would hint at widespread vegetative death. Whatever
caused the coal hiatus must have started in North America 25
million years sooner..
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
The remains of fish and various marine reptiles
(including the common pachypleurosaur
Neusticosaurus, and the
bizarre long-necked archosauromorph
), along with
some terrestrial forms like Ticinosuchus
, have been recovered from this
locality. All these fossils date from the Anisian
(about 237 million years ago).
Late Triassic extinction event
The Triassic period ended with a mass extinction, which was
particularly severe in the oceans; the conodonts
disappeared, and all the marine reptiles
except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods
were severely affected.
oceans, 22% of marine families and possibly about half of marine
genera went missing according to University of Chicago paleontologist Jack
Though the end-Triassic extinction event was not equally
devastating everywhere in terrestrial ecosystems, several important
clades of crurotarsans
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 went extinct, but other more adaptive
dinosaurs survived to evolve in the Jurassic. Surviving plants that
went on to dominate the Mesozoic world included modern conifers and
What caused this Late Triassic extinction is not known with
certainty. 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)], forming the Central Atlantic Magmatic
[(CAMP)], one of the largest known inland volcanic
events since the planet 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
At the Manicouagan impact crater, however,
recent research has shown that the impact melt within the crater
has an age of 214±1 Ma. The date of the Triassic-Jurassic boundary
has also been more accurately fixed recently, at 201.58±0.28 Ma.
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 the impact. So the evidence suggests the
Manicouagan impact preceded the end of the Triassic by
approximately 10±2 Ma. Therefore it could 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, between 12 and 17 million years apart. But
arguing against this is a recent study of North American faunas.
Forest of northeast Arizona there is a unique sequence of
latest Carnian-early Norian terrestrial sediments.
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 the Jurassic and Cretaceous, rather than the
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