Monophyly of the Passeriformes: Test of a Phylogenetic Hypothesis

ABSTR•CT.--Theorder Passeriformes was largely defined by 19th century anatomists on the basis of phenetic similarities.The purpose of this study was to determine whether the group is monophyletic in the strict contemporary sense.Similarities used by previous workers were reanalyzed to determine whether or not they could be shown to be derived character states corroborating the hypothesis of passeriform monophyly.Of 18 traditional taxonomic characters analyzed, none refuted the hypothesis of passeriform monophyly, 13 failed to corroborate the hypothesis, and 5 did corroborate it.These are the aegithognathous palate, the "passerine" tensor propatagialis brevis, the bundled spermatozoa with coiled head and large acrosome, the enlarged hallux, and the type VII deep plantar tendons.To this analysis is added new information from the hind limb musculature.Previous knowledge of oscine musculature is augmented by new information from representative suboscines.The division of M. pubo-ischio-femoralis into Pars cranialis and Pars caudalis is confirmed for suboscines, distinguishing the entire order Passeriformes from nonpasserine birds.In the foot, the loss of a set of intrinsic muscles of the forward digits, previously known from oscines, is also confirmed for suboscines.These limb-muscle characters supplement the analysis of traditional characters in corroborating the hypothesis that the order Passeriformes is monophyletic.A functional analysis of the passerine foot shows that it is a derived mechanism specialized for perching, but with a reduction in the subtlety and variety of certain other movements.