Analyses of Mesozoic archosaurs (birds, pterosaurs and dinosaurs � Hone et al., 2005; Hone and Benton, 2007) suggest that Cope�s Rule was in operation in all three lineages and that each produced increasingly large forms over their evolutionary history. Despite the functional limits of flight on morphology (and especially large size) both birds and pterosaurs were able to produce increasingly large individuals during the Mesozoic. In the former this is especially interesting as birds are expected to have been small during their early evolution. However the Ornithuromorpha actually show counter selection for small size in an otherwise growing clade, which may have facilitated their survival at the KT boundary.