EAR-PF: Mammals as sentinels of biotic recovery and the topographic diversity gradient in the aftermath of the Cretaceous–Paleogene mass extinction

Weaver, Lucas N, Seattle WA

Investigators

Abstract

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Dr. Lucas N. Weaver has been awarded an NSF EAR Postdoctoral Fellowship to investigate the ecological recovery of mammals during the Cretaceous–Paleogene (K–Pg) mass extinction event. Insight from other environmental catastrophes in Earth’s past can provide information about the current environmental crisis. Additionally, impacts of environmental disturbances are not equal across time and space; therefore, it is important to see how resilient or susceptible species are to extinction in different temporal and geographic settings. The K-Pg mass extinction event, which occurred 66 million years ago and is famous for leading to the extinction of the dinosaurs, is similar to the kind of extinction seen today. Towards this end, this project aims to study how mammal communities (including the ancient ancestors of the group to which humans belong) recovered from the K–Pg mass extinction over the first 1 million years of the ‘Age of Mammals,’ in the Denver Basin of Colorado. Mammals are often used as ‘canaries in the coal mine’ for ecological health because environmental variables such as temperature and moisture are related to mammals’ ecological health. The work is based on the hypothesis that the Rocky Mountains acted as a buffer during the K–Pg mass extinction and allowed more mammalian species to survive and diversify in a post-dinosaur world. Given that the Earth is likely in the midst of a sixth mass extinction event in its history, this study provides crucial insight into which ecosystems are at greatest risk, and which ecosystems are better able to ‘weather the storm.’ Broader impacts of this work include working with the Denver Museum of Nature and Science to disseminate results to a broad audience through their exhibits; mentoring of undergraduates at University of Michigan and City University of New York, and development of curriculum for high school students. This project aims to investigate the spatial and temporal heterogeneity of mammal recovery after the Cretaceous–Paleogene (K–Pg) mass extinction (66 million years ago) in the Denver Basin of Colorado. Denver Basin fossil localities are highly resolved chronostratigraphically, allowing precise correlation of the pattern and timing of biotic recovery in different paleogeographic regions of the basin during the first ~1 million years of the Paleogene. Since mountainous regions today are biodiversity hotspots, this project is based on the hypothesis that mammal communities close to the emerging Rocky Mountains (1) were more resistant to the K–Pg mass extinction, and (2) recovered more quickly in its aftermath. To explore these hypotheses, the work will quantify and compare the taxonomic (richness, relative abundance), dietary (inferred via tooth shape), and body mass (inferred via tooth size) diversity between two stratigraphic sequences of fossil mammal assemblages: (1) close to and (2) far from the Rocky Mountain front range. This project will involve field and laboratory work and will use new paleoecological methods to infer community-level mammal diversity patterns through time. This study will be the first to (1) look at spatial heterogeneity in post-K–Pg mammalian recovery in high resolution and (2) explore whether mountain habitats were a driver of early mammalian diversity. These results will help identify geospatial features that promote biological community resilience/reassembly after environmental disasters, and will shed light on the tempo and mode of the post-K–Pg radiation of mammals, which ultimately led to the distribution of terrestrial biodiversity we see today. This work will also integrate data from the mammal fossil record with the broader vertebrate and plant fossil record, and with paleoclimate proxies. This novel multidisciplinary approach will allow collaboration with other scientists to track whole-ecosystem recovery in the aftermath of the K–Pg mass extinction. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.