The virtual and physical preparation of the Collard plesiosaur from Bridgwater Bay, Somerset, UK

Abstract

The 'Collard Plesiosaur', found in 2003 in Bridgwater Bay on the Somerset coast is the only complete and fully articulated plesiosaur skeleton to have been found in Britain for over 100 years. The 1.5 metre long specimen was preserved in the finegrained and thinly laminated Lower Liassic Kilve Shales. This lithology is susceptible to fluctuations in humidity, severely compromising the integrity of specimens once dry. The priorities for the project were to arrest shale delamination caused by environmental fluctuations and to prepare the specimen for research. The specimen appeared to be mostly well fossilised in a homogeneous, un-cemented matrix, offering excellent potential for non-destructive recovery of fossil information using conventional X-radiography and Computed Tomography before the preparation commenced. Despite the skeleton being variably mineralised, the analyses yielded very detailed images. This 'virtual preparation' helped to inform the subsequent physical preparation, with the conventional radiographs proving most useful. In addition, the project demonstrated that such analyses are not just useful for guiding preparation but also for recording material that might be removed during preparation and highlighting details not visible to the naked eye or that remain buried. During preparation, experimental attempts to consolidate matrix samples were unsuccessful - the shale layers distorted and delaminated. However, the adhesive Paraloid B72 was successfully applied to the sides of the specimen blocks in liberal quantities, providing a useful partial barrier to future changes in atmospheric relative humidity. Scalpels were found to be the most appropriate tools for preparing the specimen, removing one paper-thin layer of shale at a time.