Z chromosome (chrZ) for all Palaeognathae and chicken Z for all Neognathae (3). To distinguish between the recombining PAR (that has nearly identical sequences between chrZ and chrW) and the region lacking recombi-nation (that has become differentiated between chrZ and chrW) along the sex chromosome, we developed an approach that involves examina- The basal bifurcation in the phylogeny of modern birds is between ostrich-like birds (ratites and tinamous; Palaeognathae) and all other birds (Neognathae). Crown birds are subdivided into two main groups, Palaeognathae and Neognathae, that can be distinguished, among others, by the organization of the bones in their pterygoid-palatine complex (PPC). Most differences between the Palaeognathae and Neognathae lie in the reduction or loss of the ability to fly, but the crania of palaeognaths are also more robust and more fenestrated than those of neognathous birds. Thus, the result is inconsistent with the traditional understanding of a basal avian divergence between Palaeognathae and Neognathae. Krista Lee, Julie Feinstein, Joel Cracraft, The Phylogeny of Ratite Birds: Resolving Conflicts between Molecular and Morphological Data Sets, Avian Molecular Evolution and Systematics, 10.1016/B978-012498315-1/50011-X, (173-211), (1997). Shape variation to the vomer, which is the most anterior part of the PPC, was recently analysed by Hu et al. The Palaeognathae or paleognaths are one of the two living superorders of birds.The other living superorder is Neognathae.Together these two clades form the subclass Neornithes.. Paleognath is a word derived from the ancient Greek for "old jaws" in reference to the skeletal anatomy of the palate, which is described as more primitive and reptilian than that in other birds. The findings suggest that the morphological characteristics of the ratites are secondarily acquired, probably through neoteny and that the ratites are descendants of flying, neognathous ancestors. Only a few, mainly cranial, morphological characters distinguish the Palaeognathae from the Neognathae (Olson, …

into the Palaeognathae and the Neognathae. The Palaeognathae is a small taxon, approximately 60 species, vs 8000 species in the Neognathae. Palaeognathae, or paleognaths (from Ancient Greek palaió-"old" + gnáthos “jaw”) is one of the two living clades of birds – the other being Neognathae.Together, these two clades form the clade Neornithes.Palaeognathae contains five extant branches of flightless lineages (plus two extinct clades), termed ratites, and one flying lineage, the Neotropic tinamous.