When was the Triassic Period?
The Triassic was from about 225 million to 190 million years
ago. It is the first period of the Mesozoic ("middle life")
The Triassic Period is most commonly believed to have begun 251 million years ago and lasted until 199.6 million years ago.
There is no Permian-Triassic period. The Permian and Triassic were two-separate geolgic period. The Permian-Triassic extinction event marks the end of the Permian period and the beginning of the Triassic period. This event was the most devastating mass extinction in Earth's history during which 90% of all life died out. It also marks the end of the Paleozoic era and the beginning of the Mesozoic.
Icthyosaurs and plesiosaurs are both known from Triassic strata. Crinoids were common then, but their history spans more than just the Triassic. Coelophysis appeared in the middle of the Triassic. Phytosaurs and aetosaurs did not survive past the end of the Triassic. Lystrosaurus was a Triassic dicynodont, about the size of a sheep, which has been found on every continent (including Antarctica). Podocarps and other gymnosperms (plants) survived beyond the Triassic period.