Tetrapod Diversity in the Purbeck Limestone group of England: Implications for Jurassic-Cretaceous Faunal Turnover

Project overview

The Jurassic–Cretaceous (J/K) transition is an interval of important faunal turnover in Mesozoic terrestrial ecosystems, occasionally hypothesized to represent a poorly understood mass extinction event.

Substantial faunal changes occur most notably within dinosaurs, where the sauropod and stegosaur-dominated herbivorous communities of the Late Jurassic are replaced in the Early Cretaceous by ornithopod-dominated communities. Other tetrapod groups such as lepidosaurs (lizards and snakes), amphibians and mammals show evidence for significant diversification around the J/K boundary.

However, understanding of faunal change has been limited by the generally poor global record of the latest Jurassic and earliest Cretaceous fossils.  

Rocks of the Purbeck Limestone Group crop out along the eastern end of the Jurassic Coast World Heritage Site in Dorset, UK, and date to the latest Jurassic to earliest Cretaceous. They formed in marginal and shallow marine environments, and have yielded >60 species of turtles, lepidosaurs, crocodilians, pterosaurs, dinosaurs and mammals.

This diversity makes the Purbeck perhaps the best site globally to examine tetrapod communities and faunal change during the J/K transition.

Most fossils are small and have most typically been collected using screenwashing to extract small teeth, jaws and other bone fragments from mudstone and marl horizons. Although this has been highly successful in increasing understanding of Purbeck tetrapod diversity, it has not been applied systematically throughout the formation to examine large-scale patterns of community structure and faunal change.   

In this field- and lab-based project, the student will systematically sample suitable horizons within the Purbeck Limestone Group both vertically through stratigraphy, and laterally at different outcrops across the coast and inland.

Vertebrate microfossils will be extracted via screenwashing, identified, and combined with historical data to assess the diversity and ecological structure of Purbeck ecosystems, and their stability and variation through time. Re-examination of historically collected fossil material may be undertaken using the collections of the Natural History Museum in London and CT scanning approaches.

All these data will be drawn together and combined with those from Late Jurassic (e.g. Morrison Formation, USA) and later Early Cretaceous (e.g. Wealden Group, England) ecosystems to better understand changes in community composition and ecological diversity through the J/K transition.

Methodology

The student will systematically target clay-rich horizons within the Purbeck Limestone Group, extending both vertically (e.g. the ‘Mammal Bed’, ‘Fern Bed’ and ‘Sly Bed’) and geographically along the coast (e.g. Durlston Bay, Worbarrow Bay, Lulworth Cove) and inland.

Sediment collected at each of these horizons will be processed using standard lab techniques to extract microvertebrates. These will be identified using literature and comparisons to the collections of the Natural History Museum (NHM): where new taxonomic groups or species are identified these will be published as standalone papers.

Computed tomography scanning (at the NHM and/or Birmingham) will be used to re-examine historically collected material of key groups to better constrain taxonomy.

These data will be combined with historical collections from literature and museums to quantify ecological diversity and structure within individual horizons and through the Group and to allow wider comparisons with Late Jurassic and Early Cretaceous communities from other localities globally.   

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.  

This project will provide a broad base of palaeobiological skills. Field- and lab-based work will include the development of skills in planning and executing fieldwork, sedimentology, palaeoenvironmental interpretation, lab-based microvertebrate processing, microfossil imaging, taxonomy and anatomy. CT-based examination of historical material will develop additional skills in CT scanning, segmentation and 3D visualisation. The analytical phase of the project will develop skills in statistical programming and quantitative analysis of diversity change.  

Partners and collaboration

Dr Susannah Maidment (NHM London) is a vertebrate palaeontologist with extensive field experience and world-leading expertise on the Jurassic–Cretaceous transition. She will support the student at all project stages, including during fieldwork, anatomical comparisons, access to NHM collections and facilities, and comparisons to other Late Jurassic and Early Cretaceous sites.   

Dr Chris Reedman (Jurassic Coast Trust) is the Head of Palaeontology for the Jurassic Coast Trust and a highly experienced field palaeontologist. He will provide key support, advice and supervision of the student during fieldwork on the Jurassic Coast, and will also facilitate links to local museums, quarries and fossil collectors.  

Further details

Further details on how to contact the supervisor for this project and how to apply for this project can be found here: 

For any enquiries related to this project please contact Professor Richard Butler, University of Birmingham, r.butler.1@bham.ac.uk.

To apply to this project:

• You must include a CENTA studentship application form, downloadable from: CENTA Studentship Application Form 2024. 
• You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities. 
• Please submit your application and complete the host institution application process via: https://sits.bham.ac.uk/lpages/LES068.htm. Please select the PhD Geography and Environmental Science (CENTA) 2024/25 Apply Now button. The CENTA application form 2024 and CV can be uploaded to the Application Information section of the online form.  Please quote CENTA 2024-B3  when completing the application form. 

Applications must be submitted by 23:59 GMT on Wednesday 10th January 2024. 

Possible timeline

Year 1

Planning of fieldwork. Systematic sampling within the Purbeck Limestone Group. Lab-based sediment processing. Museum collections work to identify suitable material for CT scanning. CT training. 

Year 2

Ongoing sediment processing. Taxonomic identification of microvertebrates. CT data acquisition and segmentation. Preparation of first paper(s) on novel components of microvertebrate assemblages. 

Year 3

Quantitative characterisation of ecological communities and variation through the Purbeck. Comparisons to other Late Jurassic and Early Cretaceous assemblages. Preparation of paper(s) on ecological diversity. Write-up of thesis. 

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