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The Triassic Period: (245 million years ago)

 

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 years.

 

During the Triassic, both marine and continental life show an adaptive radiation beginning from the starkly impoverished biosphere that followed the Permian-Triassic extinction. Corals of the hexacorallia group made their first appearance. The first flying vertebrates, the pterosaurs, evolved during the Triassic.

 

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"). 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. 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 Newark Group.

 

At the beginning of the Triassic Period, 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.

 

 

 

Life

 

The start of the Triassic followed the Permian Extinction, an event of unknown cause that wiped out over two-thirds of land-dwelling vertebrates. Taking their place were strangely mammalian-looking reptiles called cynodonts, early dinosaurs like Herrerasaurus and Eoraptor, and primitive reptiles called archosaurs, from which some dinosaurs (as well as all crocodiles) later evolved. It was during the late Triassic that the therapsids ("mammal-like reptiles") evolved into the first early mammals.

 

Except for insects, the skies of the early Triassic were relatively quiet. It was only toward the end of this period that the earliest pterosaurs, such as Eudimorphodon, appeared, and they probably weren't the most accomplished fliers.

 

 

 

Climate

 

The Triassic climate was generally hot and dry, forming typical 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, a climate suitable for reptile-like creatures. 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. It probably had strong, cross-equatorial monsoons.

 

 

The End of the Triassic Period

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, forming the Central Atlantic Magmatic Province 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 singled out.

 

 

Map of the Earth during the Triassic Period

 

 

 

 

 

 

Paleozoic Era

Mesozoic Era