WHEN AND WHERE DID LIFE RECOVER FROM THE END-PERMIAN MASS EXTINCTION?

The end-Permian mass extinction was the most devastating loss of life in Earth’s history. Evidence suggests that ecological devastation following this event was protracted and may have lasted 5 million years until the Middle Triassic (Anisian). Despite this, the timing and nature of full biotic recovery is not completely understood. Previous work has based the onset of biotic recovery on generic and species diversity and the reappearance of metazoan reefs, largely from broad global datasets. However, emerging research shows that community recovery should be based on more than these parameters, and that it can vary in time and space. Further fieldwork is needed to understand patterns of post-extinction community ecology.

Previous understanding of the timing and spatial pattern of recovery has been confined mostly to shallow water environments in low latitude settings. However it has been proposed that shallow-marine environments may have acted as refuges from toxic deep ocean conditions, and thus it is hypothesized that shallow and deep marine communities recovered very differently. Recent data has also shown that Triassic recovery has paleogeographic and clade-specific dynamics (Brayard, 2009; Song et al., 2011). But before this can be tested, a working definition of recovery needs to be established. A previous definition of recovery (Krassilov, 1996) states that a community can be considered fully recovered when normal ecosystem functioning has resumed and previous dominance and diversity are regained. The study herein has defined community recovery not only by high diversity and abundance, but also by larger organism size and high evenness and tiering.

This study aims to establish the spatial and temporal nature of ecosystem recovery following the end-Permian mass extinction. Fieldwork was conducted on the Lower Triassic (Olenekian) Anshun and the Middle Triassic (Anisian) Qingyan Formations in Guizhou Province, south China. Preliminary results indicate that while Middle Triassic benthic marine communities were characterized by high diversity, tiering, evenness, and organism size were not comparable to those of pre-extinction (Permian) communities. This demonstrates that full biotic recovery may have taken longer than previously recognized in south China.