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When did the first dinosaurs appear during the Triassic Period?
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Triassic Period
Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the early Triassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
The first dinosaurs appeared during the Late Triassic period. While their ancestors, such as small bipedal archosaurs, were present earlier in the period, the primitive dinosaurs belonging to the saurischian and ornithischian orders emerged during the Late Triassic and continued into the Early Jurassic.12