PhD: Dissecting an evolutionary transition: how ancient crocs went from land to water

Sometimes evolution takes one type of animal and turns it into something radically different, with a restyled body capable of remarkable new behaviours that allow it to colonize new environments. These so-called ‘major evolutionary transitions’ were some of the most profound events in Earth history, as they set life on radical new trajectories. Prime examples are fish evolving into land-dwelling tetrapods, running mammals turning into whales, and birds evolving from dinosaurs. However, transitions such as these remain shrouded in mystery: do they happen rapidly or gradually, and what drives them?

This project will focus on a long-neglected group of fossil crocodile relatives, the thalattosuchians. They evolved from land-living ancestors in the Early Jurassic (ca. 190 million years ago), then entered the water as semi-aquatic lagoon-dwellers called teleosaurids, before eventually losing their armour, morphing their limbs into flippers, and transforming into fast-swimming open-ocean predators called metriorhynchids. They are a prime example of a major evolutionary transition, but have never received the amount of research attention as fish with fingers or dinosaurs with feathers.

This PhD position is part of a new, three-year Leverhulme Trust-funded project. We will study the evolution of thalattosuchians in unprecedented detail, with a focus on how their biology was reshaped as they made the transition from land to water. We will subject a wealth of well-preserved fossils to high-resolution CT scanning to visualize internal neurosensory features like the brain cavity, inner ear, and sinuses, which hold the key to understanding the senses and behaviours of these animals, but which have been inaccessible to previous generations of scientists. We will map how these features changed across the family tree, in what order and how quickly, and test whether some of them were drivers of the transition.

The PhD student will work closely with the PI (Brusatte) and postdoc (Young) in Edinburgh, along with external team members Yanina Herrera, Stig Walsh, and Lawrence Witmer, to achieve these goals. The PhD project will include examination of fossil specimens in museums in the UK and internationally, CT scanning of fossils, processing the CT scans to yield digital models of the brain and sensory organs, phylogenetic analysis, and statistical analysis of macroevolution. The student will be welcomed into the dynamic, and growing, vertebrate palaeontology and geobiology research group at the University of Edinburgh. He/she will gain training in: vertebrate anatomy, phylogenetic methods and systematics, CT imaging (segmenting and rendering), scientific illustration, conference presentations, scientific publishing, networking skills, and public engagement with research (a key strength of the Edinburgh group and PI Brusatte). The PhD student will publish their work as part of several planned high-impact papers.