Foraminiferal Extinction and Size Reduction during the Permian-Triassic Transition in Southern Tibet.

The miniaturization of organisms during the Permian-Triassic mass extinction, as an ecological strategy in response to environmental devastation, has been widely recognized in diverse marine invertebrates. Previous studies on the extinction process and miniaturization of foraminifers in the Permian-Triassic interval have relied on the fossil record of the low-latitude Paleotethys or a global database, although data and materials from the high-latitude Neotethys region are still rare. To reveal the evolutionary patterns and spatial variability of foraminifers at different latitudes and paleogeographic contexts, here we investigated the fossil distribution and size variation of foraminifers in the Selong Section of southern Tibet, located in the mid-latitude Neotethys of the Southern Hemisphere during the Permian-Triassic transition. The results show that the foraminifer of the Selong Section experienced a two-pulsed extinction (total species extinction rate of 71%), consistent with the time in South China but with a lower magnitude of extinction. Meanwhile, the data show that foraminiferal test volume was significantly miniaturized following the first pulse of extinction event: the mean size of post-extinction foraminifer was only 15% of that in the pre-extinction, mainly reflected by the disappearance of large forms as well as occurrences of smaller survivors and originators. Combined with the South China record, size data from southern Tibet indicate that the miniaturization of foraminifera is synchronous in the Paleotethys and Neotethys but smaller in magnitude in the Neotethys. We propose that ocean anoxia and acidification may be the environmental pressures leading to local and global foraminiferal miniaturizations, along with global warming, which might play a dominant role. [ABSTRACT FROM AUTHOR]