Triassic period


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See also: Geologic Timescale (table)Geologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
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Triassic period

(trīăs`ĭk), first period of the Mesozoic eraMesozoic era
[Gr.,=middle life], major division of geologic time (see Geologic Timescale, table) from 65 to 225 million years ago. Great crustal disturbances that marked the close of the Paleozoic and the beginning of the Mesozoic eras brought about drastic changes in the
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 of geologic time (see Geologic TimescaleGeologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
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, table) from 205 to 250 million years ago.

Throughout the Triassic, E North America, as a result of the mountain-building episode that formed the Appalachians in the late Paleozoic eraPaleozoic era
, a major division (era) of geologic time (see Geologic Timescale, table) occurring between 570 to 240 million years ago. It is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (see each listed individually).
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, was elevated above sea level. California and Nevada, however, were submerged. In the Lower Triassic the sea extended E to Idaho, Colorado, and Wyoming; in the Middle Triassic it submerged British Columbia; in the Upper Triassic it extended into Alaska. In Lower and Upper Triassic time the west coast, from Alaska to British Columbia, was disturbed by violent and widespread volcanic activity. The Triassic formations of W North America are chiefly marine shale and limestone, with considerable igneous intrusions.

Near the end of the period, the only Triassic formation of E North America was deposited in downfaulted troughs, parallel to the Appalachians, from Nova Scotia to North Carolina. Composed of shale, conglomerate, and sandstone, this Newark series is comprised of sediments from the Appalachians. It is widely interrupted by so-called traprock—diabase dikes and sills—which forms ridges and cliffs, such as the Palisades of the Hudson near New York City. The end of the Triassic in North America was marked by extensive faulting and tilting of the Newark series, called the Palisade disturbance, and by the emergence of W North America.

The Triassic deposits of Germany form three series. In the Bunter series, the land was emergent, and red sandstone and sandy shale, with some salt and gypsum, were deposited. The Muschelkalk series saw the transgression of the land by the sea and the deposition of marine shale and limestone; the Keuper series saw the land again emergent and shale, sandstone, and gypsum being formed. In England there was no marine phase corresponding to the Muschelkalk; the Triassic of England is commonly called the New Red Sandstone. The Tethys, a great seaway, extended through the Mediterranean region E through the Middle East to the Himalayas and to E India. During the Triassic a subduction complex including an elongate volcanic arc system developed along the N American west coast. N Africa and Europe were still attached to N America as part of the supercontinent Pangaea.

The climate of the Triassic was semiarid to arid. In the plant life, marine algae were abundant, ferns and tree ferns less important than in the Paleozoic, conifers dominant among the trees, and a new group, the cycadscycad
, any plant of the order Cycadales, tropical and subtropical palmlike evergreens. The cycads, ginkgoes, and conifers comprise the three major orders of gymnosperms, or cone-bearing plants (see cone and plant). The cycads first appeared in the Permian period.
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, appeared. Many Paleozoic invertebrates appeared for the last time in the Triassic. The ammonitesammonite
, one of a type of extinct marine cephalopod mollusk, related to the nautilus and resembling it in having an elaborately coiled and chambered shell. Unlike the interiors of nautilus shells, the chambers of ammonite shells display intricately shaped septa and sutures.
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 became very important, then were reduced at the end of the Triassic to one species, but were destined to become numerous again in the succeeding Jurassic period. Amphibians were apparently not as numerous as in the Paleozoic, but some types were more highly developed. The dominant animals of the Triassic were the reptiles; although the Triassic reptiles were less specialized than those of the Jurassic, there were already a number of types of dinosaursdinosaur
[Gr., = terrible lizard], extinct land reptile of the Mesozoic era. The dinosaurs, which were egg-laying animals, ranged in length from 2 1-2 ft (91 cm) to about 127 ft (39 m).
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, pterosaurspterosaur
[Gr., = winged lizard], extinct flying reptile (commonly called pterodactyl [Gr., = wing finger]) of the order Pterosauria, common in the late Triassic and Cretaceous periods, from approximately 228 to 65 million years ago.
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, and marine reptiles. The Triassic rocks also contain the fossils of the earliest known mammals.

References in periodicals archive ?
DESERT DAYS * Some 220 million years ago, in the later part of the Triassic Period, the area lay in the arid belt north of the equator (currently occupied by the Sahara), and South Wales was a hot desert.
Scientists believe turtles appeared on land 210 million years ago in the Triassic Period before diversifying.
Examination of the assumed pattern of continents and oceans during the Triassic Period shows how this ancient seaway must have stretched from southern Europe and northern Africa across India to lands farther east.
But back in the Triassic period these giant predators would have made lakes and rivers scary places to be.
The article itself notes that this discovery pushes back the fossil record 'for this type of pterosaur' by more than 5 million years; the pterosaurs as a whole--the order of extinct flying reptiles--go back significantly earlier, to the late Triassic period.
Shonisaurus popularis was a school-bus-size, flippered marine reptile which lived in the Triassic period, 250 - 200 million years ago.
The show includes a Tyrannosaurus Rex, the terror of the ancient terrain, as well as the Plateosaurus and Lilienstemus from the Triassic period, the Stegosaurus and Allosaurus from the Jurassic period and Torosaurus and Utahraptor from the awesome Cretaceous period.
In this case, the dead zone, during the Early Triassic period which followed, lasted for a perplexingly long period: five million years.
Ten species (17 dinosaurs) are represented from the creatures' entire 200,000,000-year reign, including Tyrannosaurus rex, the terror of the ancient terrain, as well as the Plateosaurus and Liliensternus from the Triassic period, the Stegosaurus and Allosaurus from the Jurassic period, and Torosaurus and Utahraptor from the Cretaceous period.
Asilisaurus is part of the silesaurs group of creatures who evolved separately from dinosaurs and lived in the triassic period 200million-250million years ago.
Three of them are variations on a story that began 225 million to 136 million years ago during the Triassic Period when this area was locked in a dance of wind and waves, shallow seas retreating and returning, laying down sedimentary rock--the rich red sandstone and siltstone of the Spearfish Formation, chalky gypsums, the green shales of the Sundance Formation.
Ten species of dinosaur are represented from the entire 200 million year reign of the dinosaur, including the Tyrannosaurus Rex, the terror of the ancient terrain, as well as the Plateosaurus and Liliensternus from the Triassic period, the Stegosaurus and Allosaurus from the Jurassic period and Torosaurus and Utahraptor from the awesome Cretaceous period.