We would like to thank D. Stoffregen for his expert preparation of this specimen, and D. Watson of Watson Sculptures Inc. for advice on moulding and casting of the scale model. Thanks also to Drs. C. Schroder-Adams, K. Henein, M. Ryan, and A. Murray for reading earlier drafts of this paper and making many helpful comments and suggestions, and to three anonymous reviewers for making many helpful suggestions. Thanks to K. Garbrah of the Biological Sciences Department for his help converting digital file formats.