In the past years, various E ocene fossil birds were described as stem group representatives of the zygodactyl P sittaciformes (parrots). These birds show quite disparate morphologies, which cast some doubt on the correct assignment of all of them to the psittaciform stem group. A reassessment of their affinities is further needed, because it was recently proposed that among extant birds, P sittaciformes and P asseriformes (passerines) form a clade and that passerines possibly derived from a zygodactyl ancestor. Here, phylogenetic analyses are performed, which for the first time also include representatives of the Z ygodactylidae, the extinct zygodactyl sister taxon of the P asseriformes. The early E ocene P sittacopes was originally described as a stem group representative of P sittaciformes. However, none of the present analyses supported psittaciform affinities for P sittacopes and instead recovered this taxon in a clade together with zygodactylids and passerines. Also part of this clade are the early E ocene taxa P umiliornis and M orsoravis , and it is detailed that P sittacopes and the long‐beaked and presumably nectarivorous P umiliornis , with which it has not yet been compared, are very similar in their postcranial osteology. The present analysis corroborates the hypothesis of a zygodactyl stem species of passerines. To account for these results, P sittacopes is here assigned to a new higher‐level taxon and a new name is also introduced for the clade including Z ygodactylidae and P asseriformes.
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Gérald Mayr (2015) studied this question.