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Permian Triassic Systems and Their Mutual Boundary — Memoir 2, 1973
Phanerozoic Biotic Crisis
A. Lee McAlester
The well-known extinctions of marine animals near the Permian - Triassic boundary were accompanied by comparable reductions in both land animals and land plants, and by a severe drop in the rate of diversification of marine plants. Similar crises affecting much of the preserved biosphere characterized Late Cambrian, Late Ordovician, Late Devonian and Late Triassic time. With few exceptions, Phanerozoic intervals of diversification and extinction have tended to occur simultaneously in all fossilized groups — marine and terrestrial, animal and plant. This unity of biotic events imposes new constraints on theories seeking to explain periodic extinctions.
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