Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
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The Triassic
Extinction and Recovery
Origin of Mammals
Origin of the Dinosaurs
Climate and Plate Tectonics
Skull of Coelophysis
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Skull of Cynognathus
Skull of Buettneria
Bennettitalean 1
Bennettitalean 2
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Foundational Concepts
Dating Methods
Earth Processes
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Triassic 252–200 mya
Defining Characteristics:
  • • Early Triassic: the start of life’s remarkable recovery after the end-Permian extinction
  • • the origin and rise of dinosaurs and the first mammals in the Middle to Late Triassic
  • • Map of the Triassic World
Secondary Characteristics:
  • • the emergence of giant marine reptiles (ichthyosaurs) and the rapid diversification of cephalopod ammonites in the oceans
  • • the first truly modern coral reefs in the Middle Triassic

In 1834, Friedrich August von Alberti gave the name Trias (“three parts”) to three distinct rock strata in southern Germany: the Bunter (lower), Muschelkalk (middle), and Keuper (upper). These three units proved to be easily identifiable throughout Europe and were clearly younger than the underlying Permian rocks. Now geologists consider any rock layers that are the same ages as those of the Trias to belong to the Triassic Period. Triassic rocks are now known from every continent, although not all of them show these same three units. Triassic fossils provide important information about the history of life at the start of the Mesozoic Era.

At the start of the Triassic, 252 million years ago, the equatorial supercontinent of Pangea completed its formation as the final continents collided with the mainland. Polar ice caps were absent and sea level remained fairly low and stable. The climate was generally warm and arid, but moist river and lake environments sustained gymnosperm forests and large amphibians. Nevertheless, life on Earth was sparse. Only a few types of animals and plants were left after the great mass extinction at the end of the Permian, and sea life in particular was severely depleted. The repopulation of Pangea had meager beginnings, and the rediversification of life took 4–6 million years. The Early Triassic is characterized by low diversity in both marine and terrestrial habitats, but by the Middle or Late Triassic diversity had rebounded in most environments.

The first dinosaurs appeared in the early Late Triassic alongside the first flying reptiles (pterosaurs), crocodyliforms, turtles, frogs, and mammals. Terrestrial vegetation was dominated in many areas by conifers, seed ferns, and cycads. In the oceans, invertebrates such as echinoderms and corals evolved into many new species. They lived among a great variety of mollusks (such as clams and snails), sharks, and the first marine reptiles. By the end of the Triassic, the first rumblings of Pangea’s splitting apart had begun.


Overview | Extinction and Recovery | Origin of Mammals
Origin of the Dinosaurs | Climate and Plate Tectonics

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