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Smaller Protistan Evidence and Explanation of the Permian-Triassic Crisis
Protistan primary producers of the Permian-Triassic seas include the phytoplankton and benthic calcareous algae. Animal protists include the benthic foraminifera and the zooplanktonic tintinnids and radiolaria, which may be important intermediate links in marine food chains. By analogy with modern oceanic ecosystems, the fossil record of these protists can be utilized to interpret the level of productivity of the paleoecosystems.
Apparently, the Permian-Triassic crisis resulted from the coincidence of moderately adverse physical conditions with important biologic changes. Adapted to high nutrient levels in the early Paleozoic, phytoplankton decreased steadily in abundance and diversity as these levels dropped in the mid Paleozoic, dropping precipitously by latest Permian. The reduced productivity caused the extinction of most suspension feeders and higher trophic levels; only the most cosmopolitan and efficient grazers, carnivores, and detritus feeders persisted. This minimal late Permian diversity was followed by a moderate expansion in the Mid Triassic; the former diversity level was not regained until after the Late Triassic development of new groups of phytoplankton and their Jurassic expansion.
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