Admissions > PhD by research > Research Projects > Macroevolution of crocodiles

Macroevolution of crocodiles

Supervisors: Professor Michael J Benton, Dr Gavin Thomas (Biological Sciences, Bristol) and Dr Marco Andrade (University of São Paulo)


Why do plant and animal groups rise and fall in diversity through time? Why are some groups apparently highly successful and others not? The crocodiles (= crocodyliforms) have shown both modes, and therefore may provide a worthy case study for investigation of macroevolutionary models. Crocodiles today are a relatively insignificant group of only 13 species, and yet they were much more diverse in the past. Major clades expanded into key predatory, and even plant-eating, roles in the Mesozoic and Paleogene, both on land and in the oceans.

The aim of this study is to produce a complete supertree of crocodyliforms, and to use this as the basis for a wide array of studies of biodiversity, disparity (= range of morphological form), and comparative phylogenetics. Major clades will be the focus – the Thalattosuchia, marine crocodilians of the Jurassic, Notosuchia, terrestrial short-snouted forms of the Cretaceous, and Eusuchia, the modern crocodilians dating from the Cretaceous to the present. In each case, the clade expansion will be investigated – (1) Was expansion triggered by environmental change or key adaptation? (2) Do the clades follow the disparity-first or diversity-first models? (3) Are there regular patterns in body size change? (4) Does body size correlate with cranial pneumaticity, tooth form, and limb characters?

The nature of clade diversifications (‘adaptive radiations’; Simpson 1944) has not been substantially investigated with numerical methods that explore complete well-resolved, and well dated trees in terms of diversity, disparity, and appropriate comparative phylogenetic methods. There is now a good opportunity to explore this case study because of substantial recent work on crocodilian systematics (e.g. Andrade 2011; Brochu 2004), improvements in stratigraphic dating of reptile-bearing Mesozoic formations (e.g. Weishampel et al. 2004), and the development of new techniques in the study of disparity (e.g. Brusatte et al. 2008) and comparative phylogenetic treatment of character distributions over large phylogenetic trees (Thomas and Freckleton 2011).

The project will provide a broad training in numerical methods in palaeontology and macroevolution. The initial task will be to combine numerous recent cladograms of fossil crocodilians into a single composite or supertree: such work requires great care and dedication. An interest in cladistics and comparative phylogenetics is essential, and the project offers an opportunity for innovative and high-profile work contributing to current debates in macroevolution, biodiversity, and quantitative evolutionary ecology. The student will have the chance to publish a number of high-profile papers, and to acquire a training that will suit him/her for a range of research positions across the fields of evolution, ecology and palaeobiology.

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Last updated: 26/10/11