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Why is the formation of Pangea unlikely to have been the only cause of the Permian extinction?

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Line graph showing the number of marine animal families from the Precambrian era to the present, with illustrations of key groups such as trilobites, ammonoids, marine reptiles, and diatoms. The graph highlights major extinction events and a rise to 1,900 living families today. — Permian extinction The diversity of marine animal families since late Precambrian time. The data for the curve comprise only those families that are reliably preserved in the fossil record; the 1,900 value for living families also includes those families rarely preserved as fossils. The several pronounced dips in the curve correspond to major mass-extinction events. The most catastrophic extinction took place at the end of the Permian Period.

The formation of Pangea is unlikely to have been the sole cause of the Permian extinction primarily due to a significant chronological discrepancy. While the assembly of the supercontinent was completed by the first half of the Permian Period, the mass extinction events did not occur until the final 15 million years of the period.1

Although the formation of Pangea contributed to the crisis by destroying shallow-water marine habitats and altering ocean currents and regional climates, these factors alone do not account for the timing or the severity of the extinction. Scientists point to other critical drivers, most notably the prolonged eruption of the Siberian flood basalts. These eruptions are believed to have caused widespread oceanic anoxia and significant disruptions to the carbon cycle, which coincide more closely with the extinction events than the earlier completion of Pangea.1234