1. Evolutionary Morphology Section, Institute of Evolutionary and Ecological Sciences, Leiden University, Kaiserstraat 63, NL-2311 GP Leiden, The Netherlands and Photogrammetry and Remote Sensing Section, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Thijsseweg 11, NL-2629 JA Delft, The Netherlands. S.W.S.Gussekloo@Vet.UU.NL