Triassic

The Triassic (/trˈæs.ɪk/ try-ASS-ik)[8] is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya.[9] The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.[10] The Triassic period is subdivided into three epochs: Early Triassic, Middle Triassic and Late Triassic.

Triassic
251.902 ± 0.024 – 201.36 ± 0.17 Ma
Chronology
Etymology
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitPeriod
Stratigraphic unitSystem
Time span formalityFormal
Lower boundary definitionFirst appearance of the Conodont Hindeodus parvus
Lower boundary GSSPMeishan, Zhejiang, China
31.0798°N 119.7058°E / 31.0798; 119.7058
GSSP ratified2001[6]
Upper boundary definitionFirst appearance of the Ammonite Psiloceras spelae tirolicum
Upper boundary GSSPKuhjoch section, Karwendel mountains, Northern Calcareous Alps, Austria
47.4839°N 11.5306°E / 47.4839; 11.5306
GSSP ratified2010[7]
Atmospheric and climatic data
Mean atmospheric O
2
content
c. 16 vol %
(80 % of modern)
Mean atmospheric CO
2
content
c. 1750 ppm
(6 times pre-industrial)
Mean surface temperaturec. 17 °C
(3 °C above modern)

The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.[11]

The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.

The global climate during the Triassic was mostly hot and dry,[12] with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic.