New nuclear evidence for the oldest divergence among neognath birds: the phylogenetic utility of ZENK (i).

To date, there is little consensus concerning the phylogenetic relationships among neognath orders, which include all extant birds except ratites and tinamous. Different data sets, both molecular and morphologic, have yielded radically different and often unresolved ordinal topologies, especially within the neoaves clade. This lack of resolution and ongoing conflict indicates a need for additional phylogenetic characters to be applied to the question of higher-level avian phylogeny. In this study, sequences of a single-copy nuclear gene, ZENK, were used to reconstruct an ordinal-level phylogeny of neognath birds. Strong support was indicated for the oldest divergence within Neognathae; the chicken- and duck-like birds formed a clade that was sister to all other modern birds. In addition, many families of traditional taxonomic orders clustered together in the ZENK tree, indicating the gene's general phylogenetic reliability. However, within the neoaves clade, there was little support for relationships among orders, which is a result similar to all other recent molecular studies of higher-level avian phylogeny. This similarity among studies suggests the possibility of a rapid radiation of the major neoaves lineages. Despite the ongoing lack of neoaves resolution, ZENK's sequence divergence and base composition patterns indicate its general utility as a new phylogenetic marker for higher-level avian systematics.