School of Earth Sciences

The structure, function, and palaeobiology

of conodonts

Supervisors: Professor Philip Donoghue and Dr Emily Rayfield

Conodonts are a hugely diverse evolutionary lineage of primitive vertebrates, the first to possess a mineralized skeleton, manifest as a raptorial feeding apparatus used for actively seeking prey in Palaeozoic Seas, indicating that the skeleton evolved first for predation, not for protection or bodily support (Sansom et al. 1992. Science 256:1308; Purnell 1995. Nature 374:798; Donoghue et al. 2000. Biological Reviews 75:191).

Or maybe not. While this interpretation of conodont palaeobiology has entered the textbooks and, therefore, become received wisdom, sceptics have identified what they believe to be Achilles heels in the hypothesis that conodonts are vertebrates and that their skeletons performed a tooth function (Blieck et al. 2010. Geodiversitas in press). Many of these critiques centre on the nature of the mineralized tissues that comprise the conodont skeleton (Kemp 2002. Alcheringa 26:23), their inferred pattern of growth (Reif 2006. Neues Jahrbuch, Abh. 241:405), their organic matrix (Kemp & Nicoll 1996. Modern Geology 20:287), and claims of preserved amino acid residues (Kemp 2002. Journal of Paleontology 76:518) and even DNA. These critiques have implications that extend well beyond the palaeobiology of conodonts, to the use of their fossils as mineral archives of the chemistry of the oceans in which they lived (Trotter et al. 2006. Lethaia 40:97; Trotter et al. 2008. Science 321:550). All of the critiques of conodont affinity can be assessed through characterization of the mineral and organic phases that comprise conodont skeletal tissues, while competing hypotheses of conodont element function require independent testing.

The focus of this project is to apply state of the art techniques and instrumentation (i) to characterise the nature of conodont skeletal tissues with the aim of resolving debate over the biological affinities of conodonts and the physically suitability of the different tissues that comprise the conodont skeleton to serve as archives of seawater chemistry; (ii) to test hypotheses of element function, applying finite elements methods (Rayfield 2007. Ann. Rev. Earth Planet. Sci. 35:541) to virtual models of conodont element morphology. Characterization of element structure and morphology will employ Electron Back Scattered Diffraction and Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM; Donoghue et al. 2006. Nature 442:680). Virtual models of element morphology will be derived from SRXTM and converted to digital meshes for Finite Elements Analysis.

Training will be provided in the use and application of all of these instruments and techniques. The successful student will join a lively and exciting research group of graduate students and postdocs using the same techniques to address a variety of problems in palaeobiology and evolutionary biology.