PhD: 3D quantitative analysis of textures in palaeobiology: environments, taphonomy and exceptional preservation

Project Highlights:
Use state of the art instruments and quantitative approaches to address significant problems in taphonomy, exceptional preservation, and early animal origins
Develop a range of skills in experimentation and analysis, applied to palaeobiology
Join a dynamic multidisciplinary group working across the interface of geology, palaeobiology and surface metrology (engineering)

Overview
The roughness or texture of surfaces is intuitively obvious and, at a course scale, easily discernible through touch and sight. We can see and feel that some bedding surfaces are rougher than others, or that some parts of an exceptionally preserved fossils appear smoother than the matrix, or other parts of the fossil. But texture is surprisingly difficult to quantify, and until recently statistically testing whether, and the degree to which, the texture of different surfaces is comparable was not really possible. Relatively new approaches to 3D quantification have changed this, and using methods borrowed from engineering, it is now possible to detect and quantify quite subtle differences in surface texture at a range of scales, down to less than micrometres. This project will apply these techniques to a series of palaeobiological questions linked to exceptional preservation. This will include quantification of microbially induced sedimentary structures, or MISS. Microbial surfaces have important implications, for the ecology and taphonomy of Ediacaran organisms for example, but can be very difficult to distinguish from abiogenic textures (Davies et al. 2016). This project will test the hypothesis that they are distinguishable through quantitative analysis of texture. Another area of investigation will test the hypothesis that the surface texture of the soft tissue remains in exceptionally preserved fossils differs from that of the surrounding rock matrix. This is important because for some fossil species the boundaries of the body margins, and thus the shape of the body are unclear. Changes in colour can be misleading because it is difficult to distinguish between body margins and external haloes related to chemical changes around a decaying carcass. Moreover, in many fossils no compositional difference is detected between fossil and surrounding rock. What then accounts for the outline of these fossils?

Methodology
Hypotheses will be tested through quantitative analysis of surface textures based on statistical analysis of parameters derived from ISO 25178 Characterisation of Areal Surface Texture, and Scale Sensitive Fractal Analysis. Other approaches to quantification of surfaces, including Orientation Patch Count will also be used. Analysis will be based on 3D data acquired using a range of techniques, but principally focus variation microscopy, which can capture data over a range of horizontal and vertical scales and resolutions. Members of Leicester’s Centre for Palaeobiology Research have considerable expertise in this type of analysis (see further reading), but it has not been applied to the hypotheses at the core of this project. Experimental approaches to hypothesis testing will also be used as appropriate. Material will be available through supervisors, their research networks and through the project collaborators (see below).

Training and Skills
The project will involve a range of palaeontological, taphonomic and sedimentological techniques, but project specific training will include optical, Scanning Electron, and focus variation microscopy; quantitative analysis of 3D texture and complexity (using ISO approaches, OPC and other measures). Training in experimental approaches to hypothesis testing will also be provided as appropriate. The emphasis of the research will be on robust quantitative approaches and statistical hypothesis testing.

Partners and collaboration
Prof. Mark Purnell leads research on quantitative 3D analysis of texture and form, primarily to test hypotheses linking tooth wear to diet. Prof. Sarah Gabbott has developed a holistic research program focussed on how we read and interpret fossils through understanding the processes that effect how carcasses get into the fossil record. Together, they have developed a research programme on taphonomy and exceptional preservation that draws heavily on quantitative and experimental approaches.

Drs Neil Davies and Alex Liu, Cambridge University, are experts in microbial textures and their significance for exceptional preservation, particularly in the context of Ediacaran fossils.