adj. Of, relating to, or being the period of geologic time from about 251 to 200 million years ago, the oldest period of the Mesozoic Era. The Triassic Period is characterized by the presence of the supercontinent Pangaea, the diversification of land life, the rise of dinosaurs, and the appearance of the earliest mammals. See Table at geologic time. n. The Triassic Period. |
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