An evaluation of the usefulness of morphological characters to infer higher-level relationships in birds by mapping them to a molecular phylogeny

The use of genetic data to reconstruct systematic relationships has revolutionized our understanding of avian evolution. Morphology-based classifications were often in conflict because of different opinions among scholars about the relative importance of certain phenotypes. The considerable morphological variation observed among birds was codified into phylogenetic characters by Livezey and Zusi (2006) who also scored them for 150 extinct and extant taxa. Herein we have evaluated the phylogenetic signal of 1860 of these characters by mapping them to a molecular phylogeny including 102 taxa that represent all extant birds (with the underlying assumption that this tree topology is a good estimate of the evolutionary relationships among birds). The characters fit the molecular tree with a mean consistency index (CI) of 0.38. Muscle characters are the most homoplasious (CI 0.32), while characters related to integument, feathers, intestinal, respiratory, syrinx, urogenital, nervous, and reproductive organs show a considerably better fit (mean CI 0.49). We also explored what characters may unambiguously support certain basal clades that are well-supported by molecular data. We found only a few clades (e.g. Galloanserae, Procellariimorphae) being supported by unambiguous apomorphies, while many well-established clades (e.g. Pelecaniformes, Charadriiformes, Accipitriformes, Coraciiformes) lack such support entirely.