The Cambrian evolutionary ‘explosion’ is recorded by the proliferation of biomineralized structures in the fossil record. However, many ‘small shelly fossils’, remain difficult to interpret in anatomical, phylogenetic and functional terms, limiting their utility for reconstructing evolutionary patterns and processes. Middle to upper Cambrian assemblages of ‘paraconodont’ microfossils are suggested to include the evolutionary precursors to euconodont feeding elements, which are tooth-like structures that evolved independently of teeth in other vertebrates. Simple, conical paraconodont elements strongly support this evolutionary scenario (Murdock et al. 2013), but other paraconodont elements are more structurally complex, with unresolved growth modes and functional roles. Were the earliest conodonts more ecologically disparate than has been appreciated, or are ‘complex’ paraconodont elements anatomically or phylogenetically unrelated to conodonts? Resolution of this question will either constrain the origins of an extraordinary convergent radiation of ‘toothy’ vertebrates, or reveal previously unknown Cambrian bodyplans.
One reason why paraconodonts are so poorly understood is a scarcity of suitable material. This project will take advantage of a recently discovered assemblage of diverse, abundant and exceptionally well-preserved paraconodont elements from the upper Cambrian Deadwood Formation of western Canada (Fig. 1). The new specimens exhibit a unique, entirely carbonaceous mode of preservation which renders internal growth lines visible in transmitted light (Butterfield and Harvey 2012). A principal aim is to resolve the seemingly paradoxical growth patterns in Westergaardodina, Proacodus and Serratocambria, in order to test possible homologies with coniform paraconodonts, euconodonts, and extant relatives (in particular, lampreys). Several thousand paraconodont specimens have already been extracted from the rock and mounted on glass microscope slides. Undissolved rock samples are available for thin-sectioning and for specimen extraction using a bespoke laboratory procedure (Leicester), with additional material potentially available from drillcore sampling in Saskatchewan, Canada.
For a three-dimensional appreciation of complex paraconodont-element growth, comparative specimens from phosphatic ‘small shelly fossil’ assemblages will be analysed via thin sectioning (Leicester) and synchrotron radiation X-ray tomographic microscopy (data processing in Oxford). Specimens are available in museum collections and potentially from additional field sampling in Sweden. The collection of comparative data on growth and decay patterns in modern taxa including lampreys would be a useful addition, though not critical to the success of the project.
Aside from palaeobiological aspects, the project would benefit from a systematic taxonomic and taphonomic study of the new assemblage. Initial analysis suggests that many of the Westergaardodina morphotypes are new to science. A corollary of this work would be a refined biostratigraphic scheme for use in non-trilobite-bearing Cambrian strata.
This project will require a multi-faceted approach to solving palaeobiological problems. Large collections of unpublished specimens are already available for study, but additional material will be obtained via laboratory processing of rock samples for both ‘small carbonaceous fossils’ (SCFs) and ‘small shelly fossils’ (SSFs). You will be trained in the delicate art of microfossil picking and mounting for analysis. Resolving growth mode and element outlines will require advanced microscopy techniques, including scanning electron microscopy (SEM, Leicester), synchrotron radiation X-ray tomographic microscopy (SRXTM, probably at the Swiss Light Source), and transmitted light microscopy (TLM) with differential interference contrast (using Leicester’s newly acquired Zeiss AxioImager microscope). Morphological data on growth mode will be analysed using graphical and/or morphometric techniques. Testing taphonomic hypotheses will require petrographic thin-sectioning and/or experimental element dissolution, combined with basic geochemical analysis (BSEM/EDX). The project could include the dissection and microscopic examination of modern lampreys, both fresh and decayed, in Leicester’s state-of-the-art taphonomy lab.
Training and Skills
CENTA students benefit from 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research themes. You will become proficient in various laboratory procedures (chemical processing of rocks), microfossil preparation, and advanced microscopy techniques, as outlined above. In addition, advanced computerised image-processing, morphometric, biostratigraphic and/or phylogenetic techniques could be pursued according to the interests of the student and the direction of the project. You will join a thriving community of palaeobiologists at the University of Leicester, and gain a unique set of skills that will be attractive to both industrial and academic employers.
Year 1: Working on existing unpublished collections of SCF-type paraconodont elements from the Deadwood Formation: microscopic examination, imaging, and formulating hypotheses of growth mode. Laboratory extraction of new SCF material; taphonomic analysis of SCF preservation.
Year 2: Collecting comparative data from phosphatic paraconodont elements (requiring fieldwork and/or museum visits, and SRXTM) and perhaps also modern lampreys. Analysing datasets (Leicester, Oxford) to test hypotheses of growth, form, and function of paracondont elements, with broadening perspectives in functional morphology, phylogenetics, biomineralization and/or biostratigraphy.
Year 3: Continued analysis of datasets, writing of papers, and speaking at international conferences.
Partners and collaboration (including CASE)
Dr Tom Harvey has pioneered research into ‘small carbonaceous fossils’, and discovered the Deadwood paraconodonts. He is experienced in describing and interpreting the microscopic anatomy of problematic Cambrian animals, and using novel anatomical data to test broad-scale patterns and processes in evolution.
Prof. Mark Purnell has been at the forefront of innovative palaeobiological analysis of conodonts for several decades. He is a leading expert on conodont microstructure, form and function, and on the effects of decay on preserved anatomy.
Dr Duncan Murdock is interested in the origins of biomineralization, and has conducted ground-breaking research into Cambrian ‘small shelly fossils’ from across the tree of life, including para- and eu-conodont elements. He is experienced in the 3D reconstruction of microstructures using SRXTM.
Prof. Phil Donoghue is a leading expert on conodonts and SRXTM methods, and will contribute comparative material for study and additional specialist training.
Please contact Dr Tom Harvey, University of Leicester (firstname.lastname@example.org).