Abstract

A non-technical description explaining the broader significance of the project

Major mass extinctions have occurred at various times throughout Earth history. The most well-known of these happened with the demise of the dinosaurs at the end of the Cretaceous Period, but it is believed that the largest mass extinction happened at the end of the Permian Period, approximately 252 million years ago. The extinction in the marine realm was global and occurred over a relatively short time interval. However, events in the terrestrial environment are only sparsely documented. This project will examine well-exposed sedimentary rock successions that formed in lakes, rivers, and ancient soils during the time of these extinctions. This research will enable a precise documentation of the sequence of events on land, a comprehensive analysis of the environmental changes that took place before, during and after the event, and an investigation of how terrestrial animals and plants responded to these changes. The results will determine if extinctions on the continents occurred at the same time as those in the ocean and what conditions existed that may have caused such large-scale changes. Given current concern about rates of extinction, knowledge of the processes that occurred in the past will help identify the reasons behind major changes in flora and fauna. The project will develop museum exhibits and outreach programs to inform both educational and general audiences.

A technical description of the project

A comprehensive, multidisciplinary investigation of critical intervals of Earth history offers the best insights into the conditions that prevailed before, during, and after major biotic crises. The Permo-Triassic Mass Extinction is used as a model of how biological and physical systems responded to major climate changes, including those attributable to increasing greenhouse gases. Currently, the Permo-Triassic Mass Extinction is interpreted as a coupled catastrophic collapse of marine and terrestrial ecosystems, both of which experienced protracted restructuring of ecological communities and recovery of stable ecosystem dynamics. The Bogda Mountains in China contain a fully continental stratigraphy spanning the critical interval wherein fluvial and lacustrine deposits alternate with an extensive paleosol record, from which pedogenic trends and geochemical models can be derived. A paleontological record including major plant and animal groups is well-preserved. Pilot-project data show the preservation of a primary magnetization in rocks in the section, from which a robust magnetic polarity stratigraphy can be derived. There are also numerous volcanic deposits that contain primary volcanic zircons spanning the critical interval. These will be used to obtain high precision ages to establish a careful chronology. Together, these data allow evaluation of environmental and ecosystem changes that took place during the Permian-Triassic transition. Research results will be integrated into curricula at each participating academic institution, and summer outreach programs will be offered to high-school science teachers. Five educational videos will be developed for the Field Museum's award winning "The Brain Scoop" YouTube channel. Data visualizations of analytical and model results will be developed for informal education outreach in conjunction with the Visualization Studio at the California Academy of Sciences.

Project Outcomes: The history of life is punctuated by several major mass extinction events, profound biotic crises that were global in scope and witnessed extreme losses of biodiversity. A multidisciplinary approach is needed to understand the interplay of Earth systems, the environment, and life during these events, and to use these natural experiments as a source of information for mitigating modern biodiversity loss stemming from human-caused habitat destruction and climate change. The Permo-Triassic Mass Extinction (PTME), which occurred about 252 million years ago, is particularly compelling because of its scale (8090% of marine animal species alive at the time became extinct), it geologically short duration (less than one million years globally, with the main extinction in the oceans occurring over less than 100,000 years), and the central role of rising global temperatures in driving the extinction. Our research group examined a series of fossil-preserving rocks spanning the PTME that are now exposed in the Bogda Mountains of northwest China, and which document how the extinction impacted land animals and plants that at the time were living in the northeastern part of the ancient supercontinent Pangaea. We constructed a detailed model based on radiometric dates that describes the ages of different rock units exposed in the Bogda sections. This temporal framework is critical to understanding the distribution of fossils relative to the PTME as well as the rates at which animals and plants went extinct. Thanks to our model the Bogda sections are now one of the best-dated rock sequences preserving fossils of land animals from the time of the PTME. We also conducted fieldwork to collect new fossils, and reviewed occurrences of previously-collected specimens to construct a more accurate picture of turnover among species during the PTME. The results of this work show that many previous assumptions about which animals lived before or after the extinction in the area were incorrect, and our new dataset provides the foundation for a new understanding of how the extinction played out among land animals in the area. Finally, we investigated growth and life history patterns in an ancient mammal relative called Lystrosaurus that survived the extinction. We found evidence that Lystrosaurus individuals living in the immediate aftermath of the extinction experienced periodic stressful conditions that interrupted their growth, but they had higher life expectancies and grew to larger sizes than Lystrosaurus individuals living in southwestern Pangaea (in what today is South Africa). This result shows that different geographic areas were not all affected by shifting environments in the same way, and that the responses of animals to these changes also differed. In addition to work on the Bogda record, the research collaboration between U.S. and Chinese scientists fostered by this project resulted in two scientific publications examining temperature tolerances of different animals groups alive at the time of the PTME, and how differences in temperature preferences likely influenced which species survived the crisis and which went extinct. We communicated our results to the general public through an episode of the popular YouTube series SciShow, which has been viewed over 390,000 times. The project also served as a training opportunity for a female Ph.D. student and a female postdoctoral researcher. The past graduate student is now a tenure-track faculty member at the University of Oklahoma, and the postdoctoral researcher leveraged data and skills gained during this project to continue her research on the PTME as the Principal Investigator of a new grant from the National Science Foundation. Fossils collected during fieldwork in 2019 were archived at the Institute of Vertebrate Paleontology and Paleoanthropology (Beijing), and will be a permanent resource available to the scientific community. Last Modified: 12/01/2023 Submitted by: KennethDAngielczyk