1. Department of Natural Sciences, National Museum of Scotland, Chambers Street, Old Town, Edinburgh EH1 1JF, UK
2. School of Earth Sciences, University of Bristol, Wills Memorial Building, BS8 1RJ, UK
3. Division of Environmental & Evolutionary Biology, School of Life Sciences, College of Medical Veterinary & Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
4. Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming, Yunnan Province, 650091, People's Republic of China (e-mail: J.Liston@nms.ac.uk)