Final Report Summary - BRUS (The end-Cretaceous extinction and Paleogene recovery of mammals: evolution during a period of intense environmental change)
How do organisms respond to environmental change? Answering this question is an essential challenge in contemporary scientific research, as it will help us understand—and better prepare for—the rapid pace of current change. One major case study in the geological record is the end-Cretaceous extinction 66 million years ago, when a sudden asteroid strike and associated events killed off ~75% of all species, including the non-bird dinosaurs. This CIG project focused on understanding how the end-Cretaceous extinction affected the evolution of mammals, one of the groups that endured the extinction and prospered in the aftermath. The main goals were to collect and describe critical new mammal fossils from the first few million years after the extinction, place these in a comprehensive family tree of early mammals, and then use the genealogy to study long-term trends in mammal evolution and test how the extinction and post-extinction climate change affected mammalian history. Over the four years of this project, PI Brusatte’s team conducted five fieldwork trips to New Mexico that recovered important new fossils, including the new mammal species Kimbetopsalis. We have extensively used computed tomography (CT) scanning to digitally reconstruct key fossil specimens and describe the brains and neurosensory features of both Cretaceous reptiles that lived before the extinction and some of the first ‘archaic’ mammals that lived afterwards, including the taeniodont Onychodectes and the ‘condylarth’ Carsioptychus. We have used techniques such as Bayesian phylogenetic analysis and ecological statistical analyses to build family trees and study evolution trends, and have been developing new methods for quantifying rates of evolution and changes in ecological structure of fossil vertebrate communities over time. Thus far, 29 peer-reviewed papers, several conference presentations, and a large amount of public outreach have stemmed from this project, including a major pop science book written by Brusatte (The Rise and Fall of the Dinosaurs, 2018) and a major BBC television documentary that aired worldwide (The Day the Dinosaurs Died, 2017). Now that our project is finished, we feel we have completed our most important goals within the four-year window of the grant. Our work has started to provide a state-of-the-art look at how mammals endured, responded to, and thrived in the aftermath of one of the worst mass extinctions in Earth history. This CIG project has also helped the PI (Brusatte) secure both a permanent research position and a promotion at the University of Edinburgh, build his lab into a thriving centre of palaeontology research (with four postdocs, 8 PhD students, and several Master’s students), and obtain two key grants: an ERC Starting Grant (‘PalM’: 2018-2023) that directly continues the work on mammal evolution begun in this CIG grant, and a Leverhulme Trust Research Project grant on using CT scanning to understand the neurosensory anatomy of fossil species.