Triassic period

Definition

The first and shortest geologic period of the Mesozoic Era, spanning approximately 50 million years (251.9–201.4 million years ago) between the Permian and Jurassic periods. Marked by the catastrophic end-Permian mass extinction and the subsequent recovery and radiation of terrestrial and aquatic life, including the diversification of early modern insect orders and the emergence of stem-group lineages leading to extant arachnid clades.

Etymology

From the German Trias, coined by Friedrich August von Alberti in 1834 for the three characteristic rock layers (Bunter, Muschelkalk, Keuper) found in central Europe.

Example

The Triassic period witnessed the origin and early diversification of several extant insect orders, including Coleoptera (beetles) and Diptera (true flies), as well as the terrestrial radiation of arachnids such as early spiders (Araneae) and harvestmen (Opiliones) in the recovering post-extinction ecosystems.

Synonyms

• Triassic
• Trias

Related Terms

• Mesozoic Era
• Permian-Triassic extinction event
• Jurassic period
• fossil record
• chronostratigraphy
• insect evolution
• arachnid phylogeny

Usage Notes

Capitalized as a formal geochronologic unit. Specialists distinguish between the Triassic 'Period' (time) and Triassic 'System' (rocks). The period is subdivided into Early, Middle, and Late Triassic epochs, or alternatively into the Induan, Olenekian, Anisian, Ladinian, Carnian, Norian, and Rhaetian ages. In paleoentomology and paleoarachnology, Triassic deposits—particularly those of the Madygen Formation (Kyrgyzstan) and the Molteno Formation (South Africa)—yield exceptionally preserved specimens critical for understanding the early evolution of modern arthropod lineages.