Despite diverse attempts and methodologies, no consensus exists on the evolutionary relationships among the major groups of birds. As an alternative to the intuitive classifications of the past, a comprehensive morphological analysis is needed to reassess the higher-order placements of a number of critical and problematic, fossil and modern avian groups. This study will permit the completion of a several-year, collaborative assessment of the relationships among major taxonomic groups of birds based on a cladistic analysis of comparative anatomy. The study will include all modern nonpasseriform families and a number of fossil groups, and is to be rooted using theropod dinosaurs and other archosaurian reptiles. The anatomical comparisons will include the skeleton, musculature, and selected characters of the trachea and integument. The total numbers of taxa to be included number approximately 175, and surveys to date indicate that a target of 1,300 characters is reasonable for an analysis of this scale. The characters will be described uniformly using the comprehensive and precise technical nomenclature set forth in the Nomina Anatomica Avium. The resultant hypothesis will provide a critical, first estimate of the evolutionary history of fossil and modern birds based on comparative anatomy, will facilitate comparisons of estimates across different data sets, and will shed light on current controversies concerning the origin of birds.
