Tetrapod classification

The traditional palaeontological view that the mammals separated from the 'reptiles' before the origin of all other living amniotes is challenged. A radical alternative hypothesis, based on a character analysis of living tetrapods, is elaborated in which birds are considered the sister-group of mammals, crocodiles the sister-group of those two, chelonians the sister-group of those three, and squamates + Sphenodon the sister-group of those four. The living Amphibia are hypothesized to form a natural group and to be the sister-group of the Amniota. Further, I conclude that the Anapsida, Diapsida and Synapsida are paraphyletic or grade groups and no unique statements can be made about their structure.