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How did changes in sea level affect shallow marine life during the Permian Period?

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Permian paleogeography — Permian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins near the end of the Permian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

During the Permian Period, fluctuations in sea level had a profound impact on shallow marine life. The global withdrawal of seas from continental shelves and platforms significantly reduced the availability of shallow-water habitats, which were essential for many marine species.12

These lowstands, or periods of falling sea levels, were associated with extensive evolutionary turnovers and mass extinctions. As the supercontinent Pangea formed, the resulting decline in shallow marine environments, combined with restricted water circulation, likely reduced dissolved oxygen levels in remaining warm-water habitats. This environmental stress contributed to a catastrophic decline in marine invertebrate diversity, with many highly successful families experiencing severe losses.1234

Ultimately, these disruptive ecological changes, occurring over millions of years, reduced marine invertebrate faunas to crisis levels, representing their lowest diversity since the end of the Ordovician Period.34