The fossil record offers a rich resource with which to assess the timing and tempo of evolution among a wide variety of organisms. However, there is a question that underlies all of this work: just how complete is the fossil record? This question is one of the most fundamental posed by palaeontologists. Its answers have major ramifications for our understanding of deep time evolution, biogeography, ecology and diversity.
The early history of sharks (and indeed all vertebrates with jaws) is undergoing a major revision at the present time, with character acquisition and evolution, taxonomic interrelationships and timing of divergence all receiving a renewed scrutiny. Each of these depend on an understanding of the quality of their fossil record. There are a number of curious aspects of the early shark record, notably the c.50 Mya gap between the appearance of shark-like scales in the Ordovician before the first widely accepted shark teeth and, slightly younger, body fossils in the Lower Devonian. Recent analyses recover acanthodians stem-group sharks, and this result fills part of the apparent stratigraphic gap, but there remain considerable uncertainties about how the completeness of these, often poorly preserved, fossils impacts on inferences of diversity and relationships. Published reviews treat these materials indecisively at best (e.g. Brazeau & Friedman 2015).
New approaches to estimating fossil record completeness have recently been developed, and applied to the vertebrate record in both terrestrial (Mannion & Upchurch 2010) and marine (Tutin & Butler 2017) realms.
This project will seek to develop novel character completeness metric datasets for stem- and crown- group sharks through the Palaeozoic, covering the full diversity of body sizes, ecological strategies, and habitat preferences. Statistical analysis of these datasets will be used to address a series of key questions, including: (1) How complete is the early shark fossil record in comparison with other groups? (2) Is completeness impacted by ecological categories, habitat preferences, and/or body sizes? (3) Are changes in completeness correlated with major changes and shifts in global marine diversity, including evolutionary radiations and mass extinctions? (4) How do changes in completeness correlate with broader estimates of fossil record sampling through time and space?
The student will initially carry out a comprehensive literature review to extract and compile existing completeness datasets. Subsequently, new completeness estimates will be generated for a broad range of Palaeozoic clades, from both marine and freshwater environments. These estimates will primarily utilise an adapted version of the ‘character completeness metric’ (CCM). A diverse range of statistical approaches will be applied to the resulting datasets in order to answer the project’s key questions.
Training and Skills
CENTA students are required to complete 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 the student's projects and themes.
The student will receive a broad training in quantitative approaches to palaeobiology, including use of the software R. Training will also be provided in shark anatomy and systematics, stratigraphy, use of the Paleobiology Database, the presentation and publication of scientific results, and public outreach. This training will be designed to prepare the student for a career in palaeobiological research at a university or museum.
The successful candidate will have a strong background in a relevant subject such as geology, palaeobiology, zoology, biology, or ecology. Demonstrable strong quantitative skills will be highly beneficial, as will experience in programming and use of relevant software.
Year 1: Data gathering, including determining the taxonomic range of sharks to be studied and to identify suitable primary sources for the project. Training in the utility of the PaleoDB (data entry, exploration and data extraction). Development of completeness indices for sharks.
Year 2: Commence data analyses, establish robust qualitative and quantitative methods where appropriate. Research visits to key collections. Integration of palaeoenvironmental/palaeogeographic distribution database and palaeogeographic maps (using GIS). Presentation of initial results at SVPCA.
Year 3: Data analysis, correcting for sampling bias and testing. Presentation of project results at Palaeontological Association Annual Meeting. Writing the thesis will take place during the final year, but papers will be published throughout the project.
Partners and collaboration (including CASE)
Dr Sansom is an expert in the study of early vertebrates, with particular emphasis on phylogenetic and environmental diversity during the Palaeozoic. Prof Butler has extensive experience with palaeontological databases, particularly the Paleobiology Database, as well as quantitative analysis of fossil data including completeness metrics. Prof Coates is one of the leading authorities on early shark palaeobiology and phylogeny.
Dr Ivan Sansom (I.J.Sansom@bham.ac.uk)