PhD: Evolutionary Dynamics of Mass Extinctions and Recovery: The Marine Invertebrate Fossil Record

Mass extinctions destroy, and create, biodiversity. Fossils show that mass extinctions- rapid, global, and severe events eliminating ≥50% of all species on Earth- have occurred repeatedly, but diversity has always recovered (1). Despite this, the importance of mass extinctions, and even their existence, was unrecognized until the late 20th century, and much remains unknown about how extinctions drive evolution.
1. How severe are mass extinctions? To what extent can undersampling of survivors exaggerate extinction rates— or does poor sampling of victims obscure extinction(2)?
2. What separates survivors and victims? How do body size, ecology, geographic range, latitudinal distribution, and rarity affect extinction risk(2,3,4)? How does selectivity differ between mass extinction and background extinction?
3. How rapid are recoveries? To what extent do survivors refill previously occupied niches, or not? Could innovation in the aftermath, facilitated by extinction of incumbents, potentially lead to a long-term increase in diversity, or changes in ecosystem structure?
4. How does mass extinction affect biogeography? Do extinctions tend to decrease, or increase endemicity(2)? How are latitudinal diversity gradients affected by extinction?

Aims and Methods
Using terrestrial vertebrates to study extinction and biodiversity(2,3,5) is hindered by the incompleteness of the record. By contrast, the marine invertebrate record is an ideal study system because it provides a highly complete record of ecosystems, before and after extinction events, on regional and global scales. Armored invertebrates, including mollusks, echinoderms, and brachiopods also have hard shells that promote preservation, are highly diagnostic, and tell about their owners’ ecology. Furthermore, >100 years of palaeontological literature, and large-scale databases and resources including the Paleobiology Database, Treatise of Invertebrate Paleontology, and Compendium of Fossil Marine Genera provide raw data to test evolutionary hypotheses.
The student will take a quantitative approach to studying this record. Using the literature and databases, the student will collect data on the distribution of marine invertebrates through space and time, focusing on diverse clades including bivalves, gastropods, cephalopods, echinoderms, and brachiopods, as well as ecological data (size, life mode, habitat, larval ecology). These can be used to analyse changes in biodiversity, including local taxic richness, endemism, and global taxic richness. Logistic regression can be used to examine how characteristics such as geographic range size, latitudinal distribution, size, and diversity (species per genus) affect survivorship during periods of mass and background extinction. Resampling simulations will examine the effects of sampling on extinction rate. Last, PCoA can quantify functional diversity(6)- the range of ecologies-and how they change across extinction horizons.
The student will initially focus on the K-Pg mass extinction. As the most recent of the ”Big Five” extinctions it has the most complete record, and serves as a starting point for testing hypotheses. However, attempting to infer universal patterns (or their absence) in extinction and recovery requires comparing the K-Pg both against other mass extinctions, such as the E-O, Tr-J, and P-Tr events, and also against periods of background extinction.
Candidate
The project is part of a 5-year Leverhulme-funded research project to understand mass extinction and recovery. To help build the group, we seek students who are hardworking, curious, creative, and collaborative. Applicants should have a strong research background; publications and a master’s degree are desirable. A palaeontology background is not necessary but students should have a background in quantitative approaches to science, statistics, scripting, R, etc. This PhD is fully funded for 4 years with additional funding for conferences, computer, etc. We also assist students seeking external funding. Please contact Nick Longrich (nrl22@bath.ac.uk) with any questions.
Training
Your project is designed to result in published papers in major journals and prepare you to pursue a research career. You will be trained in quantitative palaeontological and ecological methods, and in collection and management of fossil and environmental data. We will develop your written work and provide coaching to help you turn your science into academic publications. You will also join the University of Bath’s Palaeontology Group, which is young but growing, with three faculty, Dr. Nicholas Longrich, Professor Matthew Wills and Dr. Daniel Field. Our group is part of the Milner Centre for Evolution, a unique research centre focused on fundamental research on major problems in evolutionary biology and training the next generation of evolutionary biologists.

1. Raup DM & Sepkoski JJ, Jr. (1982) Mass extinctions in the marine fossil record. Science 215(4359):1501-1503.
2. Longrich, N.R., Scriberas, J., Wills, M.A., 2016. Severe extinction and rapid recovery of mammals across the Cretaceous‐Paleogene boundary, and the effects of rarity on patterns of extinction and recovery. Journal of evolutionary biology DOI: 10.1111/jeb.12882.
3. Longrich, N.R., Bhullar, B.-A.S., Gauthier, J., 2012. Mass extinction of lizards and snakes at the Cretaceous-Paleogene boundary. Proceedings of the National Academy of Sciences 109, 21396-21401
4. Jablonski D (2008) Extinction and the spatial dynamics of biodiversity. Proceedings of the Academy of Natural Sciences of Philadelphia 105:11528-11535.
5. Longrich, N.R., Tokaryk, T.T., Field, D., 2011. Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary. Proceedings of the National Academy of Sciences 108, 15253-15257.
6. Knope M, Heim N, Frishkoff L, & Payne J (2015) Limited role of functional differentiation in early diversification of animals. Nature communications 6.