Typology versus transformation in the origin of birds

The questions of bird ancestry and the evolution of typically ‘avian’ features appear never-ending. This is true in the press but not in the scientific trenches, where the methods of comparative biology are productively used to settle many major questions, including the origin of birds. Opponents of the view that birds evolved from dinosaurs tend to use typological characterizations of ‘reptiles’ and ‘birds’; although they accept evolution, their approaches do not use the transformational approaches of phylogenetic systematics, against which hypotheses of evolutionary change in function, physiology and behavior should be tested. ‘Typologists’ also tend to depend on knowledge of how evolutionary processes must work, rather than on comparing independent patterns of evidence. Both typological and transformational approaches can be evolutionary, but the utility of typology is limited because it stresses taxonomic gaps rather than mosaic transitions.