The Triassic Period was the first period of the Mesozoic Era and occurred between 251 million and 199 million years ago. It followed the great mass extinction at the end of the Permian Period and was a time when life outside of the oceans began to diversify. At the beginning of the Triassic, most of the continents were concentrated in the giant C-shaped supercontinent known as Pangaea. Climate was generally very dry over much of Pangaea with very hot summers and cold winters in the continental interior. A highly seasonal monsoon climate prevailed nearer to the coastal regions. Although the climate was more moderate farther from the equator, it was generally warmer than today with no polar ice caps. Late in the Triassic, seafloor spreading in the Tethys Sea led to rifting between the northern and southern portions of Pangaea, which began the separation of Pangaea into two continents, Laurasia and Gondwana, which would be completed in the Jurassic Period.

By the start of the Triassic, all the Earth's landmasses had coalesced to form Pangaea, a supercontinent shaped like a giant C that straddled the Equator and extended toward the Poles. Almost as soon as the supercontinent formed, it started to come undone. By the end of the period 199 million years ago, tectonic forces had slowly begun to split the supercontinent in two: Laurasia in the north and Gondwana in the south. The giant ocean called Panthalassa surrounded Pangaea. Areas near the coast were pummeled by seasonal monsoons, but ocean-circulation patterns kept the isolated and vast interior warm and dry. Even the Poles were ice-free. The Tethys Ocean filled the C and was the zipper upon which Pangaea began to split apart. Earlier failed attempts at the split formed rift valleys in North America and Africa filled with red sediments that today contain the best preserved fossils of Triassic life.