Turtles as diapsid reptiles

Recent molecular studies of amniote relationships show turtles to be diapsid reptiles, related to the archosauromorph branch of saurian phylogeny. This conflicts with palaeontological data which shows turtles to be related either to anapsids, or to the lepidosauromorph branch within diapsids. Archosauromorph relationships of turtles have previously been proposed on the basis of neontological (mostly soft anatomy) characters. This paper reviews the neontological character evidence for turtle relationships and shows that most, but not all, of these characters are invalid in the reconstruction of turtle relationships within Amniota.