The Triassic period is the first of the three divisions of the Mesozoic era, which is known as "The Age of Reptiles." The period lasted for 37 million years, from 245 to 208 million years ago. The Triassic is named after a tricolor sequence of red, white and brown rock layers found in Germany.
Towards the end of the Paleozoic era, which preceded the Triassic, Earth's great crustal plates collided to form the supercontinent Pangaea. Early in the Triassic, Pangaea began to break apart again in a process that is still going on. North America, Europe, and Asia split away as one continent (called Laurasia) from South America, Australia, India, Africa, and Antarctica (known as Gondwanaland). These giant continents continued to break apart into the land masses we have today.
The Triassic began with a relatively warm and wet climate . However, deposits of fossilized sand dunes and evaporites (rocks formed from evaporation of salty and mineral-rich liquid) found in later Triassic strata suggest that the general climate was hot and dry, although some areas may have had defined rainy seasons.
Fossils found in Triassic rocks suggest that this was a period of transition, in which older forms of plants and animals died out and new ones began to appear. A major extinction had occurred at the end of the Paleozoic. Over 90 percent of marine invertebrate species (animals without a backbone) became extinct, as well as many other species of land plants and animals. Scientists hypothesize that a combination of volcanic eruptions, a global drop in sea level, climate change, or loss of habitat during the formation of Pangaea may have contributed to the extinctions.
The Triassic marked the beginning of important advances in plant life. The conifers (including pine trees) appeared to join the already flourishing ferns, cycads (a palmlike plant), horsetail rushes, and now-extinct species like seed ferns. Triassic plants had thick waxy coverings and did not usually grow as tall as modern trees. Scientists hypothesize that the tough coverings on these plants (perhaps developed to keep from drying out in the warm climate) contributed to the development of larger, blunt, rounded teeth (designed for tearing, shredding and chewing) in many animals, including dinosaurs.
Early Triassic oceans contained many different invertebrates than before. When seas reflooded the continents during the early Triassic period many changes took place in the composition of species. Many species died out following the Permian extinction and different species began to fill ecological niches. Modern reef-forming corals replaced earlier, more primitive forms.
Clams, snails, scallops, and other mollusks weathered the Permian extinction and replaced brachiopods as the most common shelled marine invertebrates. Two groups of bryozoans (small seaweed-like colonies attached to objects in shallow seawater), cryptostomate and fenestarte, became extinct. Many families of brachiopods (animals with two shells situated on the top and bottom of the animal) including productaceans, chonetaceans, spiriferaceans, and richthofeniaceans became extinct. The entire group of trilobites (early arthropods with three lobes—head, abdomen and tail that burrowed in mud or sand) died out during the Permian extinction. Calms, snails, scallops, and other modern mollusks weathered the Permian extinction. Sea stars, urchins, and sand dollars became the dominant echinoderms , over crinoids and blastoids.
Crinoids and blastoids were two groups that been previously very successful during the flower-like animals known as stalked echinoderms who attached their stalks (or bodies) to the sea floor. They had multiple food gathering "arms" that allowed them to filter water. Fishes continued to evolve and became better adapted to their watery environments. The cartilaginous fishes, represented by sharks and rays, had skeletons of cartilage , with bony teeth and spines.
The skeletons of bony fishes were primarily of bone instead of cartilage. An interesting group of bony fishes included the lungfish and the lobefin fishes. These ancestors of the amphibians had a backbone and small limbs for support, along with an air bladder (a primitive lung) that enabled them to breathe out of water for short periods.
Although, not as numerous as during the Permian period, the amphibians continued to be well represented and diverse. were diverse. One group of common Triassic amphibians was the labyrinthodonts ("labyrinth teeth"). These flat-headed creatures grew several feet in length, had sharp, conical teeth with deeply folded enamel (hence the name of the group), small limbs and very weak backbones, and spent their time in the swampy backwaters of Triassic rivers. The labyrinthodonts became extinct during the Triassic, but other amphibians, including frogs, became established.
One landmark of animal evolution during the Triassic was the success of the reptiles. Unlike amphibians, which must stay near water for much of their lives, reptiles were completely adapted to life on land and so occupied a variety of habitats, ranging from semidesert to dry uplands, marshes, swamps, and even oceans. Ocean reptiles included the dolphin-like ichthyosaurs, turtles, and large-bodied, long-necked, paddle-flippered reptiles known as plesiosaurs. Except for the turtles, all these marine reptiles are now extinct.
Triassic land vertebrates were dominated by two groups. In the early Triassic, the synapsids, the group that includes mammals and their close relatives, were the most common. One group of synapsids, the "mammal-like reptiles," shared the characteristics of both mammals and reptiles and ultimately gave rise to mammals. True mammals—small, shrewlike creatures— did not appear until the late Triassic. The other large group of terrestrial vertebrates during the Triassic was the archosaurs, which includes dinosaurs, crocodiles, and pterosaurs (flying reptiles), as well as several other now-extinct forms.
The first dinosaurs appeared in the late Triassic. Early dinosaurs include Eoraptor, Herrerasaurus, Staurikosaurus, and Coelophysis. These creatures were small, bipedal , and carnivorous . By the end of the Triassic, dinosaurs had become the most common land vertebrates, along with the pterosaurs, crocodiles, and crocodile-like creatures known as phytosaurs.
Lane, Gary A., and William Ausich. Life of the Past, 4th ed. Upper Saddle River, NJ: Prentice Hall, 1999.
Triassic period (trīăs´Ĭk), first period of the Mesozoic era of geologic time (see Geologic Timescale, 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 era, 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 cycads, appeared. Many Paleozoic invertebrates appeared for the last time in the Triassic. The ammonites 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 dinosaurs, pterosaurs, and marine reptiles. The Triassic rocks also contain the fossils of the earliest known mammals.
The Triassic Period, first of the Mesozoic Era's three periods, began about 240 million years ago and lasted for approximately 40 million years. It was preceded by the great Permian-Triassic mass extinction, which destroyed over 90% of living species. This extinction, the worst in Earth's history, was probably caused in part by the merger (late in the late Permian) of all the continental plates into a single huge land mass, Pangaea (pronounced pan-JEE-ah). This destroyed many species by producing a net loss of coastline, while Pangaea's size—one fourth of the Earth's surface—dictated an arid climate over much of its interior. The Triassic was therefore a period of adaptive radiation—the slow filling of vacant ecological niches by species evolved from survivors of the great extinction.
For the most part Pangaea remained geologically stable and volcanically inactive during the Triassic. Erosion proceeded more rapidly than mountain-building. Particles eroded from the Pangaean highlands accumulated in various basins to produce a distinctively Triassic class of reddish sandstones and shales called the red beds. It is not known why the red beds are all red; some geologists argue that the Pangaean climate encouraged iron-concentrating soil bacteria. In the late Triassic, the plates comprising Pangaea began to break up, and continental drift has subsequently distributed the red beds all over the world (North America , South Africa, Europe , Brazil).
Conifers (pine trees) and ferns were common land plants of the Triassic Period. Petrified Triassic conifers, some over 5 ft (1.5 m) across and over 100 ft (30 m) long, are found in Utah.
More than 95% of marine invertebrate species died in the Permian-Triassic extinction. During the Triassic, invertebrates slowly re-evolved diversity. Lobsters and crabs first appeared in this period.
Reptiles increased in number and variety throughout the Triassic Period. Some species took to the sea, evolving into the fish-eating plesiosaurs and ichthyosaurs. The first mammals appeared late in the Triassic Period. These were small and shrew-like, as their descendants would remain until the final elimination of the dinosaurs by an asteroid impact some 120 million years later.
The first dinosaurs also evolved in the late Triassic, but remained unspectacular by modern standards. It was not until the Jurassic Period that the most familiar species (Tyrannosaurus rex, Brontosaurus, etc.) were to evolve.
See also Archean; Cambrian Period; Carbon dioxide; Cenozoic Era; Continental drift theory; Cretaceous Period; Dating methods; Devonian Period; Eocene Epoch; Evolution, evidence of; Fossil record; Fossils and fossilization; Geologic time; Historical geology; Holocene Epoch; Miocene Epoch; Mississippian Period; Oligocene Epoch; Ordovician Period; Paleocene Epoch; Paleozoic Era; Pennsylvanian Period; Phanerozoic Eon; Pleistocene Epoch; Pliocene Epoch; Precambrian; Proterozoic Era; Quaternary Period; Silurian Period; Tertiary Period