Dissertation Research: Surviving the K/Pg Mass Extinction: the genome as a life history character in birds

Cornell University, Ithaca NY

Investigators

Abstract

Birds are among the most charismatic and broadly appreciated groups of living organisms, but the early origins of the modern bird radiation remain shrouded in mystery. One particularly vexing problem concerns the age of birds. Estimates based on the rate of DNA evolution suggest modern birds started to evolve about 160 million-years ago; the fossil record however, suggests an age that is scarcely older than 66 million years. Explaining the ~100-million-year gap in the fossil record profoundly limits our ability to understand when, how, and why modern bird diversity came to be. This project examines disagreements between molecular divergence time analyses and the avian fossil record, and studies a new hypothesis to explain the observed discrepancy. The project synthesizes data from paleontological and genomic datasets with predictions from population genetic theory. This work also paves the way for an integrative approach to studying evolutionary patterns across other branches of the tree of life. Moreover, the study investigates the effects of the K/Pg (Cretaceous-Paleogene) mass extinction, with important implications for understanding the decimation of Mesozoic dinosaurs and their resurrection in the form of modern birds. Such work may reveal fundamental clues into how and when Earth's modern biodiversity arose. Finally, the researchers will take advantage of the diverse outreach mechanisms at the Cornell Lab of Ornithology to communicate their findings to a broad audience. In the first part of the project, the researchers will study the age of modern birds using a variety of simulation, empirical and theoretical approaches grounded in the study of systematics. The researchers will use recent developments in Bayesian modeling to test the hypothesis that transient miniaturization of body size in the wake of the K/Pg mass extinction can explain a period of molecular rate acceleration in the extinction's aftermath. In the second part of the project, the researchers will study the feasibility of reconstructing unknown life history traits from extant and extinct taxa, conditioned on inferred rates of molecular evolution. A key component of the work will be to advance expertise in distributed high performance computing for phylogenetics, and in analyzing data related to avian life history evolution. In general, the research will leverage the recognition that rates of genome evolution are an important axis of life history variation to promote a progressive approach to studying paleo-life history diversity, and enable the integration of historically disparate information sources. The research will have potentially broad significance to comparative biology and phylogenetics, and may influence the field of divergence time analysis in both the short and long term.