The Dynamic Response of Marine Life to Extreme Temperature and Low Oxygen Events Following the End-Permian Mass Extinction.

Monday, 15 December 2014
Carlie Pietsch and David J Bottjer, University of Southern California, Los Angeles, CA, United States
The end-Permian mass extinction was the most devastating taxonomic and ecological crisis in the history of life on Earth. The recovery lasted 5 My making it the longest in geologic history, although the cause of the delay is still heavily debated. We find that additional environmental changes during the recovery interval reset the attempts that marine communities made toward ecological complexity, resulting in the overall appearance of a stagnant recovery.

The extinction mechanisms during the end-Permian include extreme temperature change and low oxygen environments resulting from the volcanic emission of carbon dioxide and other toxic gasses to the atmosphere. The biotic response to ancient environmental change is a direct analog for the ecological impacts of modern anthropogenic climate change.

We applied an ecological recovery rubric to benthic, sea floor dwelling, communities throughout the Early Triassic recovery in two major ocean basins. Newly collected bulk fossil data from the Moenkopi and Thaynes Formations from the Southwest US and the Werfen Formation in Italy were analyzed along with literature data. In Italy, directly following the extinction, low oxygen environments prevented an ecological rebound. Once low oxygen conditions receded, 600 kyr after the extinction, taxonomic diversity, fossil body size, and trace fossil complexity rebounded. A little more than 1 My into the Early Triassic, an extreme temperature event resulted in a reset of community complexity in both Italy and the Southwest US. The body size of gastropods and the repopulation of echinoderms were significantly inhibited as was trace fossil complexity. Low oxygen conditions that developed in the last ~2My of the Early Triassic limited diversity and body size in the Southwest United States. The stagnant recovery is re-interpreted as dynamic resets and rapid rebounds driven by environmental perturbations throughout the Early Triassic.