PhD: Climatic constraints on the distribution of terrestrial Neogene eutherian mammal diversity

Today’s placental mammals are part of the more inclusive taxonomic group, Eutheria, which first appeared ~160 million years ago (Ma). Placentalia originated either before or immediately after the Cretaceous/Paleogene (K/Pg) mass extinction (66 Ma) that killed off the dinosaurs, but experienced an explosive radiation during the early Paleogene. With projected global warming of 2.0–4.8°C over the next century, the prediction of species responses to climate change is one of the most fundamental issues facing conservationists and ecologists, with many mammalian species at risk of climatically-driven extinction. Although responses can be modelled, only the fossil record provides empirical evidence of the long-term interactions between climate and biodiversity.

Today, biodiversity decreases from the Equator to the poles. This is a fundamental pattern governing the distribution of most extant organisms, the understanding of which is critical to predicting climatically driven biodiversity loss. However, despite a long history of study, the causes of this latitudinal biodiversity gradient (LBG) remain unresolved. The fossil record offers a unique perspective on the evolution of the LBG, providing a dynamic system in which to explore spatiotemporal diversity fluctuations and to test hypotheses for the cause(s). The emerging pattern is that a modern-type LBG was not present for much of the Phanerozoic, and it is hypothesised to have formed ~30 Ma, during the descent into the current icehouse world, with a flattened LBG or temperate peak in biodiversity in the preceding greenhouse world. However, a recent study of North American fossil mammals found no clear evidence for a modern-type LBG until approximately 5 Ma.

The student will compile a comprehensive global fossil occurrence dataset for all terrestrial Neogene (23–2.6 Ma) eutherian mammals within The Paleobiology Database (www.paleobiodb.org). A large amount of this data is already entered, but non-North American regions, in particular, are not yet comprehensive. This dataset will then be used to reconstruct past diversity, as well as diversification rates, taking into account uneven sampling. Sampling-standardized diversity will then be compared with several environmental proxies. The Neogene witnessed a number of key events in mammalian history, including the Great American Biotic Interchange, and the student will attempt to answer the following macroevolutionary questions:

(1) Was the timing of fluctuations in terrestrial eutherian mammal diversity and faunal turnover globally synchronous?

(2) Was the modern-day latitudinal biodiversity gradient a consistent pattern of terrestrial eutherian mammals during the last 23 million years?

(3) Was climate a primary driver of terrestrial eutherian mammal diversity through time and space?

The ideal candidate will have a good degree in the biological, ecological or geological sciences. Although not a prerequisite, experience with programming and statistical languages such as R or Python, would be beneficial. During the course of this project, the student will receive training in the collection and management of data from fossil material, vertebrate anatomy, statistical analysis, programming, taxonomy and systematics, diversity analysis, and the oral and written presentation of scientific results. There will also be the possibility of developing a taxonomic side project. The student will also join a thriving community of palaeobiologists at Imperial College London, as well as a wider London network (including the Natural History Museum, and University College London), working on a wide variety of subjects, including the evolution of dinosaurs, mammals, crocodylians and squamates, as well as the effects of sampling on past diversity.