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

The considerable morphological variation observed among birds was codified
into phylogenetic characters by Livezey and Zusi (2006). Herein we have
evaluated the phylogenetic signal of 1,860 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, Procellarimorphae) being supported by
unambiguous apomorphies, while many well-established clades (e.g.,
Pelecaniformes, Charadriiformes, Accipitriformes, Coraciiformes) lack such
support entirely.