Villi and the phyly of Wetmore's order Piciformes (Aves)

The occurrence of villi (outgrowths, projections) on the bases of the basalmost downy barbulcs of breast-feathers is documented with scanning electron microscopy. The presence of these structures is thought to constitute a synapomorphic character for Passeriformes, Trochilidac, Capitonidac, Indicatoridae, Ramphastidae, and Picidae, which once more casts suspicion on the monophylv of Wetmore's order Piciformes.