Triassic Period, in geologic time, the first period of the Mesozoic Era. It began 252 million years ago, at the close of the Permian Period, and ended 201 million years ago, when it was succeeded by the Jurassic Period.

The Triassic Period marked the beginning of major changes that were to take place throughout the Mesozoic Era, particularly in the distribution of continents, the evolution of life, and the geographic distribution of living things. At the beginning of the Triassic, virtually all the major landmasses of the world were collected into the supercontinent of Pangea. Terrestrial climates were predominately warm and dry (though seasonal monsoons occurred over large areas), and the Earth’s crust was relatively quiescent. At the end of the Triassic, however, plate tectonic activity picked up, and a period of continental rifting began. On the margins of the continents, shallow seas, which had dwindled in area at the end of the Permian, became more extensive; as sea levels gradually rose, the waters of continental shelves were colonized for the first time by large marine reptiles and reef-building corals of modern aspect.

The Triassic followed on the heels of the largest mass extinction in the history of the Earth. This event occurred at the end of the Permian, when 85 to 95 percent of marine invertebrate species and 70 percent of terrestrial vertebrate genera died out. During the recovery of life in the Triassic Period, the relative importance of land animals grew. Reptiles increased in diversity and number, and the first dinosaurs appeared, heralding the great radiation that would characterize this group during the Jurassic and Cretaceous periods. Finally, the end of the Triassic saw the appearance of the first mammals—tiny, fur-bearing, shrewlike animals derived from reptiles.

Another episode of mass extinction occurred at the end of the Triassic. Though this event was less devastating than its counterpart at the end of the Permian, it did result in drastic reductions of some living populations—particularly of the ammonoids, primitive mollusks that have served as important index fossils for assigning relative ages to various strata in the Triassic System of rocks.

Paleoclimate

Worldwide climatic conditions during the Triassic seem to have been much more homogeneous than at present. No polar ice existed. Temperature differences between the Equator and the poles would have been less extreme than they are today, which would have resulted in less diversity in biological habitats.

Beginning in the Late Permian and continuing into the Early Triassic, the emergence of the supercontinent Pangea and the associated reduction in the total area covered by continental shelf seas led to widespread aridity over most land areas. Judging from modern conditions, a single large landmass such as Pangea would be expected to experience an extreme, strongly seasonal continental climate with hot summers and cold winters.

Triassic life

The boundary between the Paleozoic and Mesozoic eras was marked by the Earth’s third and largest mass extinction episode, which occurred immediately prior to the Triassic. As a result, Early Triassic biotas were impoverished, though diversity and abundance progressively increased during Middle and Late Triassic times. The fossils of many Early Triassic life-forms tend to be Paleozoic in aspect, whereas those of the Middle and Late Triassic are decidedly Mesozoic in appearance and are clearly the precursors of things to come. New land vertebrates appeared throughout the Triassic. By the end of the period, both the first true mammals and the earliest dinosaurs had appeared.

The first true mammals, which were very small, appeared in the Late Triassic (the shrewlike Morganucodon, for example). Although their fossilized remains have been collected from a bone bed in Great Britain dating from the Rhaetian Stage at the end of the Triassic, the evolutionary transition from therapsid reptiles to mammals at the close of the Triassic is nowhere clearly demonstrated by well-preserved fossils.

The first dinosaurs

First encountered in the Early Triassic, the archosaurs (or “ruling reptiles”) in the Triassic were small bipedal forms belonging to the pseudosuchians. Forms such as Lagosuchus were swift-running predators that had erect limbs directly under the body, which made them more mobile and agile. This group presumably gave rise to primitive dinosaurs belonging to the saurischian and ornithischian orders during the Late Triassic to Early Jurassic. The early dinosaurs were bipedal, swift-moving, and relatively small compared with later Mesozoic forms, but some, such as Plateosaurus (see the figure), reached lengths of 8 metres (26 feet). Coelophysis (see the figure) was a Late Triassic carnivorous dinosaur about 2 metres (6 to 8 feet) long; its fossils have been found in the Chinle Formation in the Petrified Forest National Park of northeastern Arizona in the United States. The dinosaur group was to achieve much greater importance later in the Mesozoic, resulting in the era being informally called the “Age of Reptiles.”

Flying reptiles

Some of the earliest lizards may have been the first vertebrates to take to the air. Gliding lizards, such as the small Late Triassic Icarosaurus, are thought to have developed an airfoil from skin stretched between extended ribs, which would have allowed short glides similar to those made by present-day flying squirrels. Similarly, Longisquama had long scales that could have been employed as primitive wings, while the Late Triassic Sharovipteryx was an active flyer and may have been the first true pterosaur (flying reptile). All these forms became extinct at the end of the Triassic, their role as fliers being taken over by the later pterosaurs of the Jurassic and Cretaceous.

Economic significance of Triassic deposits

Few mineral deposits of major economic importance were formed during the Triassic. Workable coal deposits are known from Arctic Canada, Russia, Ukraine, China, Japan, Australia, and Antarctica. Oil and gas occurrences are not common, but potentially important gas reserves have been discovered in Triassic rocks of the Western Canada Sedimentary Basin. Halite (rock salt) is mined from Triassic evaporites in England, France, Germany, and Austria. Low-grade uranium ores such as carnotite occur in continental deposits of Triassic age in the western United States.

BBC Earth: Walking With Dinosaurs Episode 1 - New Blood :shocked-dino:

A post-Apocalyptic world, at the dawn of the Dinosaurs : Triassic :posadist-nuke:

That Time It Rained for Two Million Years ☂☂☂

The Oddest Couple in the Fossil Record :ancom-heart:

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  • ilyenkov [she/her, they/them]
    ·
    2 years ago

    Basically been sick ever since I had covid over a month ago. Currently coughing up bloody phlegm :agony-acid:

    I love that my lungs are destroyed