PhD: Terrestrialisation in vertebrates using evidence from synchrotron tomography

Invasion of the land was a major transition in vertebrate evolution. A deep evolutionary divergence over 350 million years ago gave rise to amphibians (salamanders, frogs, caecilians) and amniotes (mammals and reptiles, including birds) (Hedges et al. 2015; Clack et al. 2016). Fossils from this time are rare, but provide critical data on the anatomical transformations involved in terrestrialisation, early ecological diversification, and the timing of radiations that ultimately gave rise to half of all living vertebrate species.

Westlothiana and Casineria are important early fossils that were originally reported as amniotes (Smithson 1989; Paton et al. 1999). Amniotes show significantly greater adaptation to terrestrial life than amphibians (e.g Janis & Keller 2001), and comprise many more species today. However, the specimens that would shed light on amniote origins have been difficult to study because of their delicate preservation in closed slabs of rock.

Aims of the project:

The project will use synchrotron tomographic data of both Westlothiana and Casineria. These data provide unprecedentedly well-resolved 3D data on the skeletons of these animals, which will be used to generate 3D anatomical renderings at high resolution. Combined with examination of Carboniferous tetrapod fossils worldwide, the resulting data will be used to revise our knowledge of phylogenetic relationships on the amniote stem lineage and to assess the structure and functional adaptations of the limbs and skulls of these important transitional fossils. This work will advance our knowledge of amniote origins and of terrestrialisation in vertebrates.

Clack JA 2012. Gaining Ground. Indiana University Press; Clack JA et al. 2016. Nature Ecology and Evolution 1, 0002; Hedges SB et al. 2015. Molecular Biology and Evolution 32, 835–845; Paton RL et al. 1999. Nature 398, 508–513; Smithson TR 1989. Nature 314, 676–678; Smithson TR et al. 1994. Transactions of the Royal Society of Edinburgh 84, 383–412.

Methods to be used Activities/skills:

• 3D rendering of computed tomographic (CT) datasets
• Comparative anatomy of fossil and extant species
• Phylogenetic analysis using Bayesian model-based approaches and parsimony (cladistics)
• Functional morphology CT scanning