PhD: Effects of the Cretaceous-Paleogene (K-Pg) Mass Extinction on Marine Diversity: Severity, Selectivity, and Recovery

How do mass extinctions destroy, and create, biodiversity? As the most recent of the ‘Big Five’ mass extinction events, the Cretaceous-Paleogene mass extinction at 66 Ma has the most complete fossil record, and is an ideal study system for understanding the role of catastrophic environmental change in driving extinction and evolution. The K-Pg extinction was a severe event, wiping out upwards of 75% of all species on the planet; it was a global event, hitting all continents and all oceans; and it was an extraordinarily rapid event, taking place over perhaps a decade or less. Marine microfossils and fossil pollen show that the extinction coincided with the formation of the giant Chicxulub asteroid crater in the Yucatan. Although the K-Pg event is best known for wiping out the dinosaurs, its effect was far more profound, resulting not just in the loss of dinosaurs but the elimination of an entire ecosystem— and the evolution of a new one to take its place.

Despite decades of study, much remains known about the patterns and processes of extinction and recovery in marine ecosystems. Is the K-Pg extinction as severe as generally believed, or is it possible that sampling biases could obscure the true severity of the extinctions (1)? What separated the winners and losers: how did traits such as size, ecology, geographic range (2) and clade diversity affect survival? How rapidly did the ecosystem recover in the aftermath? Did the short-term losses at the K-Pg boundary spur evolutionary innovation in the aftermath, driving a long-term increase in diversity?

Although patterns of extinction for dinosaurs and other terrestrial organisms have received a great deal of study (1-3) the fossil record is far more complete in the marine realm. This record has the potential to help answer fundamental questions about the role of catastrophic mass extinction in evolution.

To understand the dynamics of the K-Pg extinction and its recovery, this PhD will undertake a study of the K-Pg transition in the marine ecosystem. Possible directions include either a study of marine invertebrates, or marine vertebrates. A study of the marine invertebrate record would focus on analysis of published records of fossil occurrences for marine invertebrates, examining extinction rates, extinction selectivity, and the biogeography of extinction and recovery. This study would have a strong quantitative focus.

A study of the marine vertebrate record would focus on a new collection of vertebrates from the late Maastrichtian and early Paleogene of Morocco. The Maastrichtian fauna contains a diverse assemblage of mosasaurs, plesiosaurs, turtles, crocodylians, and archaic teleosts; it is perhaps the most diverse marine vertebrate fauna known from the Mesozoic. The Paleogene recovery fauna is dominated by marine crocodylomorphs, giant sea snakes, sea turtles, and modern teleosts. The record is especially rich for fish, with dozens of undescribed species. This study would would focus more on descriptive palaeontology.

This project is also a part of a major, 5-year research project at the University of Bath to understand mass extinction and post-extinction recoveries, specifically focusing on the K-Pg extinction. As part of this project, the student will join a large cohort of postgraduate students and postdocs. The PhD will provide training in a variety of skills necessary for a research career in palaeontology, including description, taxonomy, phylogenetics, quantitative methods, and research design.

In our lab, we focus on finding the right question- questions that are interesting, important, and solvable- and it is this focus on research design that guides our projects; we believe that what separates the great science from the merely good science is not how we go about finding the answer, but the questions we choose to ask in the first place. The University of Bath’s palaeontology group is young but growing rapidly, with two faculty (Dr. Nick Longrich and Prof. Matt Wills) being joined by a third member (Dr. Daniel Field) in 2017. The palaeontology group is in turn a key part of the new Milner Centre for Evolution, a unique research centre focused on doing groundbreaking research focusing on major problems in evolutionary biology.

Applicants should have strong research experience, although not necessarily in palaeontology; evidence of experience in the form of publications is desirable.

Anticipated start date: 2 October 2017.

Note: applications may close earlier than the advertised deadline if a suitable candidate is found; therefore, early application is strongly recommended.