The Triassic Period refers to a time in Earth's history from about 251 million years ago to 201 million years ago. Some synonyms for this period include the Trias, the Triassic Era, and the Lower Mesozoic Era. During this period, the world was dominated by the supercontinent Pangea, and many reptiles, including dinosaurs, first appeared. Additionally, the Triassic saw the rise of various types of marine life, including ammonites and ichthyosaurs. The end of the Triassic Period was marked by a mass extinction event, which led to the eventual dominance of dinosaurs in the subsequent Jurassic Period.