The middle episode in the history of life begins with the earliest Triassic, 247 mya, and marks the end of the ancient, Paleozoic realm. There is perhaps no more dramatic transition in biotas than that between the Paleozoic and Mesozoic. Little is known of the effects of this extinction for the terrestrial biota during this time because the stratigraphic sampling for most terrestrial groups is grossly incomplete compared to that of marine invertebrates with durable, calcified shells. Preliminary indications from some groups, though, like vascular plants, suggest that there was a gradual replacement of floras from the late Permian to Triassic, not a cataclysmic extinction (Knoll, 1984). Overall, the fossil record clearly shows that the Mesozoic is a period of modernization for terrestrial life, including the insects.

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