PhD: Constraining the Past and Future Distribution of Crocodylians

Living crocodylians (crocodiles, alligators, caimans, gharials) have low morphological diversity and are restricted to the tropics. As ectotherms, they are environmentally sensitive, and almost 50% of modern species are at high extinction risk. Although ecological models can predict the distributional response of species to environmental changes, only the fossil record provides empirical evidence of the long-term interactions between climate and biodiversity. The fossil record of crocodylians and their extinct relatives reveals a much richer evolutionary history, with the group characterised by a far broader latitudinal and ecological distribution. This poses questions as to why dramatic distributional shifts and diversity declines occurred in this group through time. Ecological niche modelling is a widely applied tool for forecasting future distributions of species under different climatic scenarios. Most studies only use environmental data based on the modern distribution of species, but the fossil record provides information on past distributions under different climates, augmenting our knowledge of the full ecological limits of a species. The student will reconstruct ancient abiotic niches for crocodylians and their extinct relatives through geological time, using this to quantitatively evaluate the effects of climatic change on the distribution of their diversity. They will then utilise the fossil record of extant taxa to improve the forecasting of their distributions under future climate scenarios. This innovative project sits at the interface of palaeontology and macroecology, within the growing field of conservation palaeobiology. The student will develop cutting-edge analytical skills that can be applied to any fossil or living group of organisms.

Further reading:

Chiarenza et al. 2019. Ecological niche modelling does not support climatically-driven dinosaur diversity decline before the Cretaceous/Paleogene mass extinction. Nature Communications 10: 1091.

Lima-Ribeiro et al. 2017. Fossil record improves biodiversity risk assessment under future climate change scenarios. Diversity and Distributions 23: 922–933.

Mannion et al. 2015. Climate constrains the evolutionary history and biodiversity of crocodylians. Nature Communications 6: 8438.

Saupe et al. 2019. Climatic shifts drove major contractions in avian latitudinal distributions throughout the Cenozoic. PNAS 116: 12895–12900.